Chemistry

Decomposition of water considering the volume of gas produced


Visualization of the electrolysis

Fig.1
electrolysis

During electrolysis, there is a closed circuit: electrons transport the charge within the metallic lines, while the cations and anions within the solution.


Amount of substance

the Amount of substance (outdated Mole amount or Moles) with the symbol n is a base quantity in the International System of Units (SI) and indirectly indicates the number of particles in a portion of the substance. The unit of the amount of substance is the mole, an SI base unit. Particles can be atoms, ions, molecules, formula units or electrons. Formula symbol and particle type X are combined as nX or n(X) indicated. An amount of substance of 1 mole (n = 1) corresponds to about 6.022 · 10 23 particles, see Avogadro's constant. The Avogadro constant NA. is the proportionality factor between the amount of substance n and the number of particles N(X): n(X) NA. = N(X). & # 911 & # 93

Amount of substance and the quantities derived from it, such as concentration of substance, amount of substance and ratio of substance, are important in stoichiometry. The use of the quantity of substance shifts considerations of chemical reactions from the atomic or molecular range to weighable substance masses with a very high number of particles.

For the amount of fabric nX and the crowd mX a substance portion of a substance X and its molar mass M.X the following relationship applies:


Table of contents

During the chemical reaction, chemical bonds are broken and new ones are made. The specific properties of the raw materials disappear. The newly created substances have other specific properties, such as color, odor, viscosity, density, freezing point or fixed point, boiling point and optical activity, etc.

Each reaction has a different reaction speed.

Their mechanism proceeds according to principles such as substance association synthesis, addition reaction, substance breakdown analysis, elimination reaction and substance rearrangement (exchange and substitution reactions):

  • Redox reaction, * acid-base reaction (protolysis), * complex formation reaction / ligand exchange, * precipitation reaction / precipitate formation, organic substitution (radical, electrophilic, nucleophilic).

When a chemical reaction arises at least a news Substance (product) - in physical processes it is not the substance-specific properties that change, but only physical properties such as heat content, physical state and expansion. However, all chemical reactions are also accompanied by physical changes in the substances. The release or absorption of energy, changes in the physical state or the color can be observed.

(The distinction between chemical reaction and physical process cannot be clearly defined in exceptional cases, so the dissolution of sodium in liquefied ammonia gas is considered a chemical reaction because the liquid turns blue. After the ammonia has evaporated, however, sodium remains and not - as in In the event of a chemical reaction, it would be expected - some combination of sodium and nitrogen.)

In a chemical reaction, chemical substances are converted into other substances. Depending on whether elements or compounds occur in the starting materials or products, a distinction is made between two basic types of reaction:

Synthesis edit

Material union - two elements come together to form a connection: A + B → AB

  • The Elements magnesium and Iodine form the connection Magnesium iodide
  • The elements hydrogen and fluorine react to hydrogen fluoride:
  • The Elements hydrogen and oxygen form the connection water

Analysis edit

Material decomposition - A compound is broken down into its elements: AB → A + B

Example: Water is broken down into oxygen and hydrogen by electrolysis or at 2000 ° C:

All other types of reactions (regrouping of substances) can be put together from analysis and synthesis:

Easy implementation edit

Here one element reacts with a connection, whereby another element and a new connection arise:
A + B C → A B + C < displaystyle mathrm >

Chlorinated water reacts in a similar way with sodium bromide solution. Hexane then turns orange instead of pink-violet.

A simple implementation can be imagined composed of the two partial reactions analysis and synthesis:

Duplicate implementation edit

Here two connections react with each other in such a way that two new connections are created:

Example: If a solution of magnesium iodide is mixed with a solution of lead chloride, yellow lead iodide precipitates and magnesium chloride remains in the solution.

A double conversion can be imagined as composed of two analysis and two synthesis reactions:

Other options edit

  • In the gross equation of photosynthesis, the compounds water and carbon dioxide create the compound glucose and the element oxygen.

Acid-base reactions, redox reactions and complex formation reactions can all be traced back to the donor-acceptor principle. In these cases, the products are created through the exchange of elementary particles between the starting materials.

Acid-base reactions edit

These reactions are based on an exchange of protons between the starting materials. They can be viewed as a special case of double implementation (see above). An acid and a chemical base are always used as starting materials. The acid as a proton donor releases at least one proton to the base as a proton acceptor.

Example: Hydrochloric acid is formed when hydrogen chloride gas is dissolved in water. The ampholyte water serves as the base.

Acid-base reactions can be broken down into two partial reactions, both of which are referred to as protolysis:

Example: Hydrogen chloride gas reacts with ammonia gas to form solid ammonium chloride (salmia).

Example: Ammonia reacts with the ampholyte water, which now functions as an acid, to form a basic solution.

A special case of the acid-base reaction is neutralization, in which an acidic solution reacts with a basic solution to form a neutral solution. The actual neutralizing reaction consists in the fact that oxonium hydronium ions of the acid react as proton donors with hydroxide ions of the base as proton acceptors to form neutral water:

Displacement reactions: The stronger acid (or the chemical base) displaces the weaker acid (or base) or its gaseous anhydride from their salts.

Sulfuric acid releases sulfur dioxide from sulphites and hydrogen chloride from chlorides; concentrated hydrochloric acid releases hydrogen sulphide from sulphides and hydrogen cyanide from cyanides. Sodium hydroxide / caustic soda releases ammonia from amines and ammonium compounds.

Redox reactions edit

These reactions are based on an exchange of electrons between the starting materials. They can be the basis of all four basic forms of chemical reactions. A reducing agent and an oxidizing agent are always used as starting materials. The reducing agent as electron donor releases at least one electron to the oxidizing agent as electron acceptor.

Example: Elemental copper is deposited on a zinc rod (reducing agent) that is immersed in a solution with copper (II) ions (oxidizing agent) (see cementation). The solution is enriched with zinc (II) ions.

Redox reactions can be divided into the partial reactions oxidation and reduction disassemble:

Chemical burns are redox reactions that always have elemental oxygen as the oxidizing agent.

When extracting metals from ores, carbon or carbon monoxide is used as a reducing agent (see iron extraction).

Complex formation reactions edit

In a complex formation reaction, electrons are also exchanged - but here they are made available to a central atom (usually a cation as Lewis acid) by molecules or ions in the form of lone pairs of electrons (the ligand as Lewis base. This is how copper (II) reacts, for example -ions with ammonia solution:

  1. Preservation of the elements: Educts and products contain the same elements. No elements can arise or disappear. (This conservation law was adopted by Daniel Sennert Formulated in 1618. It means a rejection of the alchemists' claim to be able to produce gold from non-gold-containing materials, provided that this project is understood physically.)
  2. That Law of the Conservation of Mass: The sum of the mass of the starting materials is equal to the sum of the mass of the products. (1. Basic Law of Chemistry, Joachim Jungius, 1662 and Michail Wassiljewitsch Lomonossow, 1748). Example: 1.00 g iron and 0.57 g sulfur react completely to form 1.57 g iron sulfide (FeS).
  3. That Law of constant proportions states that chemical compounds contain the elements in an unchangeable mass ratio that is characteristic of the respective compound. (2nd Basic Law of Chemistry, Jeremias Benjamin Richter]], 1792 and Joseph-Louis Proust, 1799). Example: When iron reacts with sulfur to form iron sulfide, only a mixture of iron and sulfur in a mass ratio of 1: 1.75 reacts completely. In the case of iron disulfide (iron pebbles), the mass ratio is 1: 0.875.
  4. That Law of Multiple Proportions means that in different compounds that contain the same elements, the mass ratios are themselves in the ratio of whole numbers. (3rd Basic Law of Chemistry, John Dalton, 1808) Example: The mass ratio of iron sulfide (1.75) is related to the mass ratio of iron disulfide (0.875) as 2: 1
  1. That Principle of constant volume proportions means that in reactions in the gas phase, the volumes of the starting materials are in relation to the volumes of the products in the ratio of whole numbers. (Derived from the 2nd + 3rd basic law of chemistry and Avogadro's law on constant molar volumes, Joseph Louis Gay-Lussac and Alexander von Humboldt, 1808) Example: In the synthesis of ammonia from the elements, the volumes are nitrogen, hydrogen and ammonia in a ratio of 1: 3: 2.
  2. Educts and products contain the same number of element atoms (cf. 1. + 2. Basic Law of Chemistry). This is achieved in a reaction equation with given formulas of the substances by suitable choice of the coefficients.
  3. The sum of the electrical charges of the educts is equal to the sum of the electrical charges of the products. (Charge equalization)

Every chemical reaction takes place with the participation of energy, since the loosening and tying of chemical bonds is connected with the conversion of energy.

Involved forms of energy edit

Depending on the type of energy involved, different types of reactions can be distinguished:

  • at thermochemical reactions heat is absorbed from the environment (endothermic reactions) or given off to the environment (exothermic reactions). In principle, all chemical reactions can be activated by supplying thermal energy, just as fundamentally, with every energy conversion during a reaction, heat occurs as a "friction loss".
  • Electrochemistry deals with reactions that take place with the participation of electrical energy. (See electrolysis, galvanic cell, battery, accumulator, fuel cell and galvanoplasty).
  • Photochemical reactions are either triggered by light (examples: photosynthesis, bromination of alkanes, curing of plastics by UV light in dental technology) or take place under the appearance of light (example: luminol reaction)
  • Some reactions can also be triggered mechanically, such as the decomposition of trinitrotoluene / TNT.

Response Path and Energy Balance Edit

The thermodynamics of a reaction describe the course of a reaction from an energetic point of view.

A chemical system strives to adopt a state that is as low in energy as possible (enthalpy minimum) and the highest possible degree of disorder (entropy maximum).

Process of an Exothermic Reaction

The starting materials are initially in a metastable state. By briefly supplying a certain amount of energy, the activation energy (activation enthalpy), the system is lifted into the unstable state. Activation sets the reaction in motion and runs independently without any additional energy supply. In the overall balance, the chemical system gives off energy to the environment, it is known as the enthalpy of reaction. The products are now in a stable condition. (For the stability of systems see also system properties)

Example: Coal burns with the oxygen]] in the air with the development of heat (exothermic) to form carbon dioxide.

If the activation energy is very low, the reaction can be set in motion without additional external energy input. The necessary activation energy is withdrawn from the environment. The reaction takes place spontaneously.

Process of an Endothermic Reaction Edit

The starting materials are initially in a stable state. By continuously supplying a certain amount of energy, the sum of activation energy and enthalpy of reaction, the system is lifted into the unstable state. If the energy supply is interrupted, the reaction also stops. In the overall balance, the chemical system absorbs energy from the environment, it is known as the enthalpy of reaction. The products are now in a metastable state.

Catalysis edit

By using catalysts, the activation enthalpy can be reduced in both endothermic and exothermic reactions. In autocatalysis, the resulting products act as catalysts for their formation.

Example: Autocatalytic formation of silver in the developer bath, see photography.):

Endergonic and exergonic reactions edit

If the change in entropy is included in a reaction, the Gibbs-Helmholtz equation is required for energetic considerations:

T = temperature in Kelvin
ΔG = change in free enthalpy
ΔS = change in entropy (at 298 K) from ΔS = Σ - Σ
ΔH = enthalpy change (at 298 K) from ΔH = Σ - Σ

In endergonic reactions, ΔG is positive, in exergonic reactions, ΔG is negative.

A chemical reaction only takes place by itself if the free enthalpy of reaction ΔG is negative.

Possible ways of interpreting the free enthalpy:

  • It is a measure of the stability of a chemical system.
  • It is a measure of the “voluntariness” or “driving force” of a reaction. With its help, it can be decided whether a reaction (after possible activation) can take place without additional energy input.
  • It is the maximum usable energy for living beings.

Some chemical reactions take place only very slowly or not at all, although they would be possible from a thermodynamic point of view. However, these reactions can also be accelerated by suitable reaction conditions (see reaction rate chemistry:

  • Increase in the degree of division and mixing and thus increase the reactive surface area in solid-state reactions. Example: Burning a lump of coal takes longer than burning the same amount of powdered coal blown into a stream of air.
  • Increase in the concentration of the reactants. Example: Carbon burns faster in pure oxygen than in the same amount of air.
  • Increase in temperature. See RGT rule

The kinetic gas theory of physics makes an important contribution to the modeling of the conditions of a chemical reaction at the level of the smallest particles.

  1. Educt particles are only converted into product particles if they collide with sufficiently high energy. In the case of large molecules, the collision must also take place in the right place. A substrate molecule has to hit the substrate binding site of its enzyme exactly. Elsewhere on the enzyme, no reaction would be possible, even if the energy was high enough.)
  2. Not all particles have the same energy, so that in a reaction mixture there will also be collisions between particles with too low an energy. There is no reaction, only an elastic shock.
  3. Whether and how quickly a reaction takes place depends on the probability with which reactant particles that have the necessary minimum energy or more will meet.

Ways to increase the likelihood of a "successful" collision:

1. Temperature increase: The higher the temperature, the more particles have the required minimum energy or more.

2. Increase in concentration: The higher the concentration of the reactants, the more likely it is that particles with the right energy will meet.

Since the concentration of the starting materials decreases in the course of the reaction and the concentration of the products increases, the rate of the reaction decreases over time. The optimization of these reaction conditions is particularly important on an industrial and industrial scale.

For a detailed representation of the laws see Kinetics], Reaction Kinetics and Enzyme Kinetics

There are chemical reactions that do not take place completely. Even if the starting materials are mixed in a stoichiometric ratio, starting materials are still present at the end of the reaction.

Example: A stoichiometric mixture of light yellow iron (III) chloride and colorless potassium rhodanide solution reacts to form deep red iron rhodanide (“theater blood”). If ferric chloride is added after a while, the color will deepen. This means that unused potassium rhodanide was still available. The color can also be deepened by adding potassium rhodanide.

Hydrogen chloride reacts almost completely with water in an acid-base reaction. After the reaction has ended, there are no more hydrogen chloride molecules (H-Cl), only chloride (Cl -) and oxonium ions (H3O +) as products. Hydrogen chloride dissociates practically completely in water, its degree of dissociation is 100%. This mixture is called hydrochloric acid designated.

Acetic acid, on the other hand, does not dissociate completely in water; at the end of the reaction, 99.96% of undissociated ethanoic acid molecules are still present, the rest have reacted with water to form acetate ions.

Observations of this kind have led to the concept of reversible (reversible) chemical reactions and chemical equilibrium:

In principle, all chemical reactions are reversible, and the products can react back to form starting materials. The reaction from the starting materials to the products becomes Forward reactionfrom the products back to the starting materials Reverse reaction called.

In the reaction equation, the reversibility of a reaction is shown by the "chemical" double arrow:

The definition of the forward reaction corresponds to the reading direction from left to right. The reverse reaction then corresponds to the reverse reading direction.

  • Acetic acid reacts with water in a reversible reaction to form acetate and oxonium ions.
  • Reaction of iron chloride with potassium rhodanite to form iron rhodanite.

If the experimental conditions are not changed for reversible reactions, this will occur after some time chemical equilibrium a. The concentrations of the starting materials and products no longer change, although the back and forth reactions still continue. These unchangeable equilibrium concentrations are related to one another which is characteristic of the reaction and the reaction conditions.

For more information, see chemical equilibrium, equilibrium constant, acid constant, mass action constant, law of mass action and steady state.

In the case of reactions that seem to be complete, such as hydrogen chloride in water, the equilibrium is practically on the side of the products. The forward reaction is favored, the reverse reaction practically does not take place.

For the reaction of acetic acid with water, the equilibrium is on the side of the educts. Here the reverse reaction has a stronger influence on the equilibrium position than the forward reaction.

For educts that do not react with one another, the equilibrium is practically completely on the side of the educts.

There are different types of chemical reactions:

  • Precipitation reaction
  • Acid-base reaction
  • Redox reaction
  • Complex formation reaction and ligand exchange
  • Chemistry addition and hydrolysis
  • Elimination
  • substitution

at Additions two molecules come together to form a single one. (Opposite: decomposition)

at Condensation When two molecules come together to form a single one, they repel small molecules such as water or ammonia. (Opposite: hydrolysis)


at Polycondensations and PolyIn addition, many small molecules (monomers) react to form giant molecules (polymer. This is how proteins are formed from amino acids, for example.

  • According to reactions typical of the substance class or bond:
    • Production of ions and ion compounds
    • Reduction of ores to metals
    • Combustion reactions (are always redox reactions)
    • Decomposition reactions (analyzes on the whole)
    • Precipitation reactions
    • Representation reactions (syntheses in the broader sense)
    • Polymerization, polycondensation, polyaddition (giant molecules are formed)
    • According to the physical state of the substances involved
      • Gas reactions
      • Reactions in solution (chemistry) | solution
      • Reactions in the melt
      • Solid reactions
      • Surface reactions
      • According to the type of reacting particles or reaction mechanisms
        • Ion reactions, radical reactions, molecular reactions, complex formation reactions
        • Reaction scheme for symbolic representation of the reaction
        • transition state
        • Kolmogorov equation, for the mathematical description of chemical reactions with diffusion and saturation terms
        • Michael Wächter: Substances, particles, reactions. Verlag Handwerk und Technik, Hamburg 2000, pp. 154-169 ISBN 3-582-01235-2

        Also teach and describe chemical reactions and their implementation, e.g. in the laboratory / in the form of detection reactions:

        • Gerhart Jander: Introduction to the inorganic-chemical internship. S. Hirzel Verlag, Stuttgart 1990 (in 13th edition), ISBN 3-7776-0477-1
        • Bertram Schmidkonz: Practical course in inorganic-qualitative analysis. Ferd. Dümmler Verlag, Bonn 1998, ISBN 3-427-43351-X

        Source: Wikipedia, article chemical reactions, German edition, list of authors see discussion page.


        Table of contents

        Under field conditions all solid particles of the mineral soil are covered with water films that are in equilibrium with the water vapor pressure of the soil air. As long as this state is maintained, there is no direct contact between the soil particles and the gas phase in the soil. These water films make a very strong contribution to the thermal conductivity of the soil, because the air in the soil has an insulating effect and the heat conduction through the soil particles hardly occurs due to the few contact surfaces. Heat conduction is only made possible by the presence of even the smallest amount of water.

        The gas phase in the soil is usually limited to the coarse pores under our field conditions. The middle pores form the basis of the usable field capacity (nFK), and the fine pores are occupied by the dead water.

        In terms of distribution, it can generally be assumed that the proportion of gas decreases with increasing depth and thus closer to the groundwater surface (GWO), since the water content increases here. Deviations from this can be found as soon as large amounts of water are applied to the soil surface, which then seep into the soil, e.g. B. after heavy rain or sudden flooding. The gas phase is divided into air channels, which are in contact with the atmosphere, and air pockets, so-called inclusions. The latter form when water flows down from a higher layer and temporarily clogs the air ducts because the air cannot escape from them quickly enough. This happens, among other things, with the above-mentioned heavy rain or overflows. Inclusions can also form under anaerobic conditions if there is enough easily decomposable organic material. Here microorganisms then produce H, among other things2 and CH4. This is particularly noticeable when the water content in the soil decreases, i.e. the water tensions increase and the gas absorption capacity of the water decreases. The hydrogen and methane formed are then in gaseous form and thus form the inclusions. The increasing water content towards the depth influences the distribution of the gas phase insofar as the decreasing water tension causes the air to migrate into the pores, in which the radii of curvature of the air bubbles allow the least air overpressure compared to the surrounding water. This means that the gas phase is limited to a few coarse pores with increasing depth.

        The composition of the gas phase in the soil sometimes differs considerably from the distribution of the gases in the atmospheric air. This means that there are much higher levels of CO in the soil2- Levels that can be up to five times higher at a depth of around 1.5 m than in the atmosphere. On the other hand, the O2-Content decreases by about the same factor with increasing soil depth. This is mainly due to the biological processes in the soil. The root respiration of higher plants, respiration of soil animals (microbial respiration, see also soil respiration) and metabolic processes of the aerobic and anaerobic microflora consume considerable amounts of oxygen and in return they form carbon dioxide. Under O2- Deficiency, i.e. under reducing conditions, also small proportions of CH4, H2S, N2O, NH3, H2 and gases of the hydrocarbon group, which generate the floor-typical odors, are formed. The high water vapor content of the soil air is remarkable. The relative humidity in the soil is usually always close to 100%. The H begins only when it is very dehydrated2O vapor pressure to decrease, this happens at water tension values ​​beyond the PWP (wilting point), i.e. pF & gt 4.2. This fact contributes to the fact that most soil organisms and plants are not adapted to survive at lower water vapor contents in the soil. The high H2O vapor pressure is created by the finely branched pore system and the very large interfaces between water and air in relation to the volume. Furthermore, the composition of the gas phase depends on the temperature, as this affects the solubility of the individual gases in water differently. So is O2 Better water-soluble at low temperatures than, for example, N2which means that the oxygen content is lower at low soil temperatures than at higher ones.

        The energetic position of the gas phase will only be dealt with briefly here in connection with the pressures occurring in the gas phase. We can calculate the water pressure in the ground using the basic hydrostatic equation. In this equation, the air pressure is used as a constant quantity in order to be able to calculate the absolute water pressure with its help:

        p W < displaystyle p _ < mathrm >> is the water pressure to be calculated, p L < displaystyle p _ < mathrm >> is the atmospheric pressure, h < displaystyle h> is the height of the water column, d W < displaystyle d _ < mathrm >> is the density of the water and g < displaystyle g> is the acceleration due to gravity. This equation shows that the water pressure is the sum of atmospheric pressure and the pressure exerted by the water column above the measuring point. This method produces only minor errors, since air pressure differences quickly equalize in an air body due to the lower viscosity of the air compared to water. For this reason, the influence of the air to be displaced or flowing in can generally be neglected when investigating water absorption or water release. However, since this influence cannot be ignored in principle, it is customary when discussing the partial potentials of the soil water to include a gas potential Ψ g < displaystyle Psi _ < mathrm >> to define. (This differs from the pressure potential Ψ h < displaystyle Psi _ < mathrm >> or Ψ p < displaystyle Psi _ < mathrm

        >>.) As already described, in the event of heavy rain or flooding, gas inclusions can form, in which pressure differences arise compared to atmospheric pressure. These pressure differences can be up to 20 hPa, depending on the height of the overflowing water column. The trapped air transfers the pressure exerted by the water column almost immediately to the solid particles and the water surrounding the air bubble. In this way, the potential equilibrium is not changed and, apart from the change in volume of the gas inclusion caused by the ambient pressure, there is no flow of air masses. The pressure inside such an enclosed body of air corresponds to the sum of the outside air pressure and the water pressure. This means that the pressure within such an inclusion can also be calculated using the basic hydrostatic equation.

        In this case, the pressure within such an inclusion is lower than the atmospheric pressure. The models mentioned so far assume that the air bodies in the ground are separated from the water by flat interfaces. This is by no means the case in the narrow pore system of the soil, because the interfaces between air and water always form curved menisci, the surface tension and radius of which compensate for the pressure differences between water and air. Viewed from the air, these menisci are concave. As a result, the pressures within the air space are higher than in the surrounding water. This pressure difference has the amount:

        The constant fluctuations in the production of carbon dioxide and the consumption of oxygen over the course of the year and the day, as well as the above-mentioned urge for air inclusions to get into the largest possible pores, lead to transport processes in the soil. Different movements are possible here:

        Diffusion movements can arise when different distributions of the soil air components and thus different partial pressures occur. Mass flows, on the other hand, require differences in the total pressure, so they only occur if the total gas mass is unevenly distributed.

        Diffusion edit

        Diffusion is the most important transport process in the gas phase. Two diffusion flows are predominant in the soil: On the one hand, the transport of CO2 from the depths upwards, on the other hand the opposing current of O2 down into the solum. In order for a diffusion flow to occur, changes in the concentrations and thus in the partial pressures are necessary. The gas flows that occur can be expressed by Fick’s 1st law:

        Therefore one can also write for the concentration c as the ratio between mass m and volume V:

        This reveals the possibility of considering the partial pressures instead of the concentrations. For using the partial pressures one then obtains:

        These transformations make it possible to work with the partial pressures as well as with the concentrations. The diffusion coefficient D records the hindrance of diffusion due to the different shape and size of the diffusion paths in the pore system. It is therefore a soil characteristic.

        Since a partial pressure gradient is necessary for the diffusion movements in the soil, gas particles can only be transported in this way if the partial pressure gradient is not interrupted by diffusion-inhibiting zones. These can be cultivation horizons (plow bottom) or compacted soil horizons. They form diffusion barriers, for the overcoming of which a large amount of the available concentration gradients is used up. Only slight diffusion movements are then possible behind such a barrier.

        Mass flow edit

        The term mass flow is understood to mean transport processes in which the total amount of gas changes. Changes in pressure are therefore necessary in order to induce a mass flow. Such changes in pressure in a gas-filled room are possible according to the general gas law:

        The following mean: m = mass of the enclosed gas, R = gas constant, p = pressure, V = volume and T = temperature. Changes in pressure in the gas phase can occur due to changes in atmospheric pressure and changes in temperature. The influence of the outside air pressure is relatively small, however, so a change of 30 hPa only causes a change in volume of about 1/30. This means that in a 1 m thick layer of soil, only 2-3 cm of air is transported out or in. The displacement of soil air by water, e.g. B. by rapid changes in the groundwater levels due to damming, as occurs in floodplain soils. This can lead to an exchange of almost the entire gas volume. The influence of temperature changes in its effect on pressure changes in the gas phase is similarly low as that of the outside air pressure. A significant mass flow can occur when new gas molecules form in the soil, as is the case under anaerobic conditions in the presence of easily decomposable organic matter. The gas flow occurring here is occasionally much larger than the diffusion flow of oxygen directed into the soil, so that reducing conditions are established.

        Edit redistributions

        Redistributions play a role when considering the air inclusions described. The delimiting menisci of such air pockets all have the same radius. The pressure inside the inclusions is higher than in the surrounding water. The menisci in the coarsest pores involved in the inclusion are therefore shallower than those in smaller pores. The air inclusions are pressed into these coarsest pores, as they can form the largest hemispherical meniscus there and thus achieve the lowest pressure difference compared to the surrounding water. This process forces the entire amount of air to be shifted towards the coarsest pores.

        Regarding the gas balance, the regular changes in the gas content should be mentioned, which are closely related to the course of the seasons. The change in the air content is caused by the increase or decrease in the water content. The water content is relatively high in spring, only to decrease over the course of summer and as the vegetation continues to develop. In return, the air content increases. The gas phase is not only limited to the space above the GWO, but gases can also be found below the GWO. These are mostly in water-dissolved form or are located in bubbles enclosed by the water. The diffusion movements of oxygen and carbon dioxide also play a role in the gas balance. In the case of oxygen, the concentration decreases with increasing depth; in the case of carbon dioxide, it increases analogously.If the air content in the soil drops to around 4–6% of the total volume, the gas volume begins to split up into individual inclusions. This gas content also forms the limit below which the O2–Partial pressure to below 18%, i.e. the content of O2 in the atmosphere, sinks. Below this limit, the characteristics of anaerobic processes appear. This limit of 4–6% air content also applies to the thriving of most cultivated plants.


        Table of contents

        Processing bread made of air

        From the work of Justus von Liebig, it has been known since the middle of the 19th century that the uptake of nitrogen compounds is a basis for the growth of crops. [3] The necessary nitrogen compounds were added to the arable soil via manure, compost or a specific crop rotation. Due to the rapid growth of the world population in the 19th century, the associated high demand for nitrogen fertilizers could no longer be met by natural occurrences of guano or Chile's nitrate, for example, or by technical sources such as coke oven gas. To point out this fact, the British chemist William Crookes stopped in June 1898 before the British Association for the Advancement of Science a widely acclaimed speech in Bristol. In it he stated that by 1918 the demand for nitrogen compounds would far exceed the supply and the western world was threatened with a famine of unimagined proportions. He went on to say that the only solution to this problem was to chemically fix the nitrogen in the air. [5] [6] He called the technical implementation of this process one of the great challenges for chemists of his time. The attempt to bind atmospheric nitrogen in a chemical that plants can absorb, known under the catchphrase “Bread from Air”, then advanced to become one of the focal points of chemical research at the time. [7]

        Early developments edit

        A first breakthrough in the fixation of atmospheric nitrogen came in 1898 with the preparation of calcium cyanamide according to the Frank-Caro method, in which calcium carbide absorbs atmospheric nitrogen at high temperatures and thus fixes it. The hydrolysis of calcium cyanamide provides ammonia and calcium carbonate. [8] Although large capacities were built up for the production of calcium cyanamide, the process was not competitive in the long term because of the high energy requirement of around 190 gigajoules per ton of ammonia. [9]

        In 1900, Wilhelm Ostwald registered a patent for the "production of ammonia and ammonia compounds from free nitrogen and hydrogen" because he had apparently succeeded in producing ammonia catalytically from the elements. As early as 1903, the Rottweiler explosives manufacturer Max Duttenhofer published Ostwald's warning of a saltpeter embargo in the event of war in the "Swabian Mercury". [10] Ostwald withdrew his patent after Bosch had proven that the ammonia produced came from the iron nitride of the catalyst used. [11]

        The Birkeland-Eyde process, which was developed by the Norwegian scientist Kristian Birkeland and his business partner Sam Eyde and put into operation in 1903, fixed atmospheric nitrogen by oxidizing it directly to nitric oxide using an electric arc. Upon cooling and further oxidation, nitrous oxide was formed, which reacted to nitric acid by absorption in water. [12] The low energy efficiency soon led to the process being displaced.

        Basic work edit

        In 1904 Fritz Haber, who at that time was working as an associate professor for technical chemistry in Karlsruhe, began to deal with the chemical principles of ammonia synthesis. The equilibrium constant found for the synthesis of ammonia from the elements nitrogen and hydrogen corresponded to a yield of less than 0.01 percent at a temperature of 1000 ° C and normal pressure and was therefore too low to implement a technical process. Haber was aware that higher pressures would lead to better yields, but due to the anticipated technical problems, he temporarily stopped his research in this area. Only a scientific discussion with Walther Nernst about the equilibrium constant of ammonia synthesis based on the Nernst theorem prompted Haber to continue his work. [7] As a result of further research, he considered the transfer to technology only possible at temperatures below 300 ° C and only with a suitable catalyst. [13] The practical implementation he succeeded shortly afterwards with the help of an osmium-based catalyst. [14]

        On October 13, 1908, Haber applied to the Imperial Patent Office in Berlin for patent protection for a “method for the synthetic preparation of ammonia from the elements”, which was granted on June 8, 1911 with patent no. 235,421. Since he was now working with BASF, he gave the company the patent for commercial use.

        Technical realization edit

        The provision of the raw material hydrogen in particular, which until then was only available in larger quantities in chlor-alkali electrolysis, required completely new processes. Also for the construction of the chemical reactors required for ammonia synthesis, in which hydrogen could be controlled at high pressures and temperatures, there were no references in technology until then. Carl Bosch and Fritz Haber then developed new solutions in many areas of technical chemistry and reactor construction. [16]

        Due to the large number of specialists required to implement manufacturing on an industrial scale, Bosch founded an interdisciplinary chemical engineering division in which mechanical engineers and chemists worked together. Since the steels initially used for reactor construction eroded by hydrogen that had diffused in atomically, one of the tasks of the new work area was to research material damage caused by decarburization of carbon steels. This ultimately led to the development of high-alloy chromium-nickel steels that withstand hydrogen attack at the required reaction temperatures and pressures. In particular, the Schierenbeck winding process developed by Julius Schierenbeck, in which several layers of hot metal tape were shrunk onto a chemically resistant central tube, made it possible to build larger and safer high-pressure reactors. [17] At the same time, Alwin Mittasch developed and tested around 3000 different catalysts based on iron oxide with various conversion-accelerating substances, which he called activators or promoters, in 20,000 experiments. [18] [19] The catalyst used in 2015 still largely corresponded to that developed by Mittasch.

        In 1913, BASF commissioned a plant based on the Haber-Bosch process at the Ludwigshafen-Oppau plant for the first time. The capacity of the plant was initially 30 tons per day. [4] As early as 1914, the German Chief of Staff Erich von Falkenhayn pushed the further development of the process up to its industrial applicability, whereupon Bosch made the so-called saltpeter promise. This was a contract for the delivery of nitrates with purchase guarantees and with financial support from the Reich for the construction of corresponding plants. [20] This should enable ammonium nitrate as a basis for military explosives to be produced in sufficient quantities without the naturally occurring saltpetre that is otherwise used. Shortly afterwards, the Haber-Bosch process succeeded in producing correspondingly large quantities of the war material. This enabled the German Empire, cut off from nitrogen sources such as Chile's nitrate by the British naval blockade, to maintain its ammunition and fertilizer production during the First World War and to avert economic collapse. In addition to the large-scale plant in Oppau near Ludwigshafen, others in Leuna and Bitterfeld were built by BASF and, after the merger in the large German corporation, by I.G. Colors operated. [21]

        After the First World War edit

        After the war, the victorious French power signed an agreement to oblige BASF to surrender all patents and experience relating to the process and to support the establishment of a corresponding factory in Toulouse. [22] Additional ammonia plants were built at the same time in England, Italy and other countries. This construction project was based either on a license from BASF or on a process variant with modified process parameters, including the Casale process and the Mont-Cenis process with modified catalyst. [4]

        In the period between the world wars, I.G. Farben with Carl Bosch as its first chairman of the board. As early as 1926, the company's market capitalization, which now has 100,000 employees, was around 1.4 billion Reichsmarks. The global economic crisis that began with the New York stock market crash of October 1929 reduced the demand for synthetic ammonia considerably. Production in Germany, which had already reached an annual volume of over 800,000 tons, then fell to below 500,000 tons and I.G. Colors halved. [24] Nevertheless, I.G. Colors until 1930 the world's largest producer of ammonia 65 percent of the total profit was accounted for by the ammonia synthesis.

        The import embargo for nitrogen fertilizers issued by the Brüning cabinet allowed I.G. Paints to increase the prices of synthetic fertilizers again. After Hitler came to power, the Nazi regime took control of I.G. Colours. In response to pressure from the Nazi regime, Bosch resigned his position on the board in 1935, which fell to Nazi Party member and military economic leader Hermann Schmitz. [25] In 1940 ammonia production in Germany reached one million tons per year. [23] As a result of the steadily increasing demand for ammonia and its secondary products, ever more powerful reactors were created.

        After World War II edit

        The increasing availability of inexpensive crude oil and cost-reducing gasification processes through, for example, the partial oxidation of crude oil fractions made it possible to set up Haber-Bosch plants all over the world after the Second World War. Originally developed by I.G. The partial oxidation developed by Farben was improved by the company Imperial Chemical Industries (ICI) and expanded to include the oxidation of naphtha, which made the raw materials of the process cheaper in the 1950s and 1960s. [4]

        Engineering companies such as M. W. Kellogg subsequently developed more energy-efficient and therefore more cost-effective large-scale plants with only one reactor, which led to a worldwide increase in plant capacity. Increasing competition and high cost pressure finally paved the way for the LCA process from ICI and the KAAP process from Kellogg, Brown & amp; Root, in which a ruthenium catalyst was used for the first time. [4]

        Ammonia is created in an equilibrium reaction from the elements hydrogen and nitrogen according to the equation

        whereby the required nitrogen is taken from the ambient air. The oxygen, which is also contained in the air but is undesirable, was first converted into water by reduction with hydrogen and separated in this way. The Fauser process used the nitrogen that was not converted during ammonia combustion with air as a raw material. Later, the nitrogen production by air separation according to the Linde process proved to be more economical. [16]

        The largest part of the production costs is caused by the procurement of hydrogen, which was initially obtained from cost-intensive chlor-alkali electrolysis. [16] With natural gas, crude oil, coal and the electrolysis products of water, other sources for the production of hydrogen were added later. [27]

        BASF used water gas based on the coal gasification of lignite using a Winkler generator as the primary source. The hydrogen is obtained by reacting steam with glowing coke. The air supplied is dosed in such a way that the oxygen is completely converted into carbon monoxide. The nitrogen required for the subsequent ammonia synthesis remained in the water gas. The carbon monoxide was then converted into easily removable carbon dioxide or used in a water-gas shift reaction to provide additional hydrogen. [16] In 2008, about 18 percent of the hydrogen produced worldwide was produced with the raw material coal. [27]

        Although natural gas was not yet available to BASF as a raw material for the production of hydrogen in the 1920s, Carl Bosch already initiated the development of the steam reforming of methane, which would later become an important part of the process. Georg Schiller achieved a breakthrough for I.G. Farben, who succeeded in steam reforming methane using a nickel oxide catalyst. The Standard Oil of New Jersey was granted a license that began in 1931 with the production of hydrogen by steam reforming at their facility in Baton Rouge, Louisiana. [29] The steam reforming of natural gas accounted for around 48 percent of global hydrogen production in 2014, around 60 percent of which used the Haber-Bosch process. [30]

        Another possible method of producing hydrogen is partial oxidation. Hydrocarbons derived from natural gas or petroleum are gasified with oxygen and steam in an open reactor without a catalyst at around 1100 ° C and the synthesis gas is processed further as in steam reforming. The higher hydrocarbons from petroleum contributed 30 percent to the annual production of hydrogen in 2008. [27]

        Hydrogen can also be obtained by electrolysis of water. This converts water into hydrogen (H.2) and oxygen (O2) disassembled. This process is only economical if inexpensive electrical energy, for example from hydropower, is available. In 2008, electrolysis accounted for around four percent of hydrogen production. [27]

        With the advent of platforming capabilities in the United States in the mid-1950s, a petrochemical hydrogen source became available that in 1956 provided about eleven percent of the hydrogen required for ammonia synthesis in the United States. [31] Later, other refinery processes such as hydrodesulfurization and hydrocracking used the hydrogen produced.

        To lower the activation energy and the associated increase in the reaction rate, an additional substance, the catalyst, is used in many chemical processes, which is not consumed during the reaction. If the physical state of the catalyst differs from that of the actual substances that react with one another, it is a heterogeneous catalyst. This is also the case with the Haber-Bosch process, in which finely divided iron on an iron oxide carrier in solid form serves as a catalyst within a reacting gas mixture. This heterogeneous catalyst, also known as “contact”, is created during the reaction from another material previously introduced into the reactor, the “catalyst precursor” or “precursor contact”.

        Iron catalyst edit

        The heterogeneous iron catalyst is a catalytically very active form of body-centered cubic α-iron and is produced by chemical reduction from a special form of oxidized iron, magnetite (Fe3O4). The effect of the catalyst is enhanced by oxidic promoters that have been added to the magnetite beforehand. In the case of ammonia synthesis, these include, for example, aluminum oxide, potassium oxide, calcium oxide and magnesium oxide. [19]

        The production of the required magnetite contact requires a special melting process in which the raw materials used must be free of catalyst poisons and the promoter surcharges must be evenly distributed in the magnetite melt. Rapid cooling of the magnetite melt, which has a temperature of around 3500 ° C, forms the desired catalyst with high activity, which reduces its abrasion resistance. Despite this disadvantage, the rapid cooling method is often preferred in practice. [32]

        The reduction of the catalyst precursor magnetite to α-iron is carried out with synthesis gas directly in the production plant. The reduction of the magnetite initially takes place via the level of wüstite (FeO), so that contact is formed with a core made of magnetite, which is surrounded by a shell made of wüstite. The further reduction of the magnetite and wustite phase leads to the formation of α-iron, which together with the promoters forms the outer shell. [4] The processes involved are complex and depend on the reduction temperature. At lower temperatures, wüstite disproportionates into an iron and a magnetite phase; at higher temperatures, the dominant process is the reduction of the wüstite and magnetite phases to form iron. [33]

        The α-iron forms primary crystallites with a diameter of about 30 nanometers. These form a bimodal pore system with pore diameters of around 10 nanometers, which result from the reduction of the magnetite phase, or from 25 to 50 nanometers, which result from the reduction of the wüstite phase. [4] With the exception of cobalt oxide, the promoters are not reduced.

        When iron oxide is reduced with synthesis gas, water vapor is produced as a by-product.This water vapor must be taken into account for optimal catalyst quality. If this comes into contact with the finely divided iron, this leads, especially in connection with high temperatures, to premature aging of the catalyst due to recrystallization. For this reason, the vapor pressure of the water in the gas mixture formed during catalyst formation is kept as low as possible, with values ​​below 3 gm −3 being aimed for. For this reason, the reduction is carried out at high gas exchange, low pressure and low temperatures. The exothermic nature of the ammonia formation ensures a gradual increase in temperature. [32]

        The reduction of fresh, fully oxidized catalyst or precursor to full capacity takes four to ten days. [32] The wüstite phase becomes faster than the magnetite phase (Fe3O4) and reduced at lower temperatures. After detailed kinetic, microscopic and X-ray spectroscopic investigations, it could be demonstrated that wüstite is the first to convert to metallic iron. This leads to a density inhomogeneity (gradient) of the iron (II) ions, as a result of which they diffuse from the magnetite through the wustite to the interface and precipitate there as iron nuclei.

        In technical practice, pre-reduced, stabilized catalysts have gained a significant market share. They already have the fully developed pore structure, but have been oxidized again on the surface after production and are therefore no longer pyrophoric. The reactivation of such prereduced catalysts only takes 30 to 40 hours instead of the usual time span of several days. In addition to the short start-up time, they have further advantages with their higher water resistance and lower weight. [32]

        Composition of a contact [34] % Iron % Potassium % Aluminum % Calcium % Oxygen
        Volume composition 40,5 0 0,35 0 2,0 1,7 53,2
        Surface composition before reduction 0 8,6 36,1 10,7 4,7 40,0
        Surface composition after reduction 11,0 27,0 17,0 4,0 41,0

        Catalysts Other Than Iron Machining

        Since the industrial introduction of the Haber-Bosch process, many efforts have been made to improve it, resulting in significant advances. In the improvement of the ammonia synthesis catalyst, however, there has been no significant progress for a long time since the 1920s.

        As part of the search for suitable catalysts, many metals were intensively tested: The prerequisite for suitability is the dissociative adsorption of nitrogen (the nitrogen molecule must therefore be split into two nitrogen atoms during adsorption). At the same time, the bonding of the nitrogen atoms must not be too strong, otherwise the catalytic capabilities would be reduced (i.e. Self-poisoning). The metals in the periodic table of the elements to the left of the iron group show such a strong bond to nitrogen. The associated formation of volume or surface nitrides, for example, makes chromium catalysts ineffective, they poison themselves. Metals to the right of the iron group, on the other hand, do not adsorb nitrogen to a sufficient extent to be able to activate sufficient nitrogen for ammonia synthesis. Haber himself initially used osmium and uranium as catalysts. Uranium reacts to nitride during catalysis and osmium oxide is very rare, volatile and highly toxic. [35]

        Because of its comparatively low price, great availability, ease of processing, lifespan and activity, iron was ultimately chosen as the catalyst. For a production capacity of 1800 tons per day, for example, a pressure of at least 130 bar, temperatures of 400 to 500 ° C and a reactor volume of at least 100 m³ are required. According to theoretical and practical studies, the scope for further improvement of the pure iron catalyst is limited. It was not until 1984 that the iron catalyst was modified by cobalt that it noticeably increased its activity.

        Second Generation Catalysts

        Catalysts based on ruthenium show a higher activity at comparable pressures and lower temperatures and are therefore referred to as second generation catalysts. Their activity is strongly dependent on the catalyst support and the promoters. A large number of substances can be used as carriers, in addition to carbon these are magnesium oxide, aluminum oxide, zeolites, spinels and boron nitride. [36]

        Ruthenium activated carbon catalysts have been used industrially since 1992 in the "KBR Advanced Ammonia Process" (KAAP, dt. Approx further developed ammonia process according to Kellogg, Brown and Root) used. [37] The carbon carrier is partially broken down to methane, which can be mitigated by a special treatment of the carbon at 1500 ° C and thus helps to extend the life span. In addition, the finely dispersed carbon poses a risk of explosion. For these reasons and because of its low acidity, magnesium oxide has proven to be a good alternative. Carriers with acidic properties remove electrons from ruthenium, make it less reactive and undesirably bind ammonia to the surface. [36]

        Catalyst poisons edit

        Catalyst poisons reduce the activity of the catalyst. They are either part of the synthesis gas or come from impurities in the catalyst itself, whereby the latter does not play a major role. Water, carbon monoxide, carbon dioxide and oxygen are temporary catalyst poisons. Sulfur, phosphorus, arsenic and chlorine compounds are permanent catalyst poisons. [32]

        Chemically inert components of the synthesis gas mixture such as noble gases or methane are not actually catalyst poisons, but they accumulate through the cyclization of the process gases and thus reduce the partial pressure of the reactants, which in turn has a negative effect on the catalytic conversion. [38]

        Synthesis conditions edit

        Change of Keq with temperature for equilibrium
        N2 (g) + 3H2 (g) ⇌ 2NH3 (g) [39]
        Temperature (° C) Keq
        300 4,34 × 10 −3
        400 1,64 × 10 −4
        450 4,51 × 10 −5
        500 1,45 × 10 −5
        550 5,38 × 10 −6
        600 2,25 × 10 −6

        The ammonia synthesis takes place with a nitrogen to hydrogen ratio of 1 to 3, a pressure of 250 to 350 bar, a temperature of 450 to 550 ° C and using α-iron as a catalyst according to the following equation:

        The reaction is an exothermic equilibrium reaction that takes place with a reduction in volume, the mass action constant of which is K.eq results from the following equation:

        Since the reaction is exothermic, the equilibrium of the reaction shifts to the side of the ammonia at lower temperatures. Furthermore, four parts by volume of the raw materials produce two parts by volume of ammonia. In accordance with the principle of least constraint, high pressure therefore also favors the formation of ammonia. A high pressure is also necessary in order to ensure that the surface of the catalyst is adequately covered with nitrogen. [41]

        The ferrite (α-Fe) catalyst is produced in the reactor by reducing magnetite with hydrogen. This is optimally effective from temperatures of around 400 to 500 ° C. The activation barrier for the cleavage of the triple bond of the nitrogen molecule is greatly reduced by the catalyst, but high temperatures are necessary for an adequate reaction rate. At the chosen reaction temperature, the optimum lies between the decomposition of ammonia into the starting materials and the effectiveness of the catalyst. [42] The ammonia formed is continuously removed from the reaction system. The volume fraction of ammonia in the gas mixture is around 20%.

        The inert components, especially the noble gases such as argon, must not exceed a certain content in order not to lower the partial pressure of the reactants too much. To remove the inert gas components, part of the gas is drawn off and the argon is separated in a gas separation system. The extraction of pure argon from the cycle gas is possible using the Linde process. [43]

        Large-scale implementation processing

        Modern ammonia plants produce more than 3000 tons per day in one production line. The following diagram shows the structure of a Haber-Bosch system.

        Depending on the origin of the synthesis gas, it must first be freed of impurities such as hydrogen sulfide or organic sulfur compounds, which act as catalyst poisons. High concentrations of hydrogen sulfide, which occur in synthesis gas from smoldering cokes, are removed in a wet cleaning stage such as the sulfosolvan process, while low concentrations are removed by adsorption on activated carbon. [44] Organosulfur compounds are separated by pressure swing adsorption together with carbon dioxide after the CO conversion.

        To produce hydrogen by means of steam reforming, methane reacts with water vapor with the aid of a nickel oxide-aluminum oxide catalyst in the primary reformer to form carbon monoxide and hydrogen. The energy required for this, the enthalpy ΔH, is 206 kJ / mol. [45]

        The methane gas is only partially converted in the primary reformer. In order to increase the yield of hydrogen and to keep the content of inert components as low as possible, in a second step the remaining methane gas is converted with oxygen into carbon monoxide and hydrogen in the secondary reformer. [45] For this purpose, the secondary reformer is charged with air, and the nitrogen required for the subsequent ammonia synthesis also enters the gas mixture.

        In a third step, the carbon monoxide is oxidized to carbon dioxide, which is referred to as a CO conversion or water gas shift reaction.

        Carbon monoxide and carbon dioxide combine with ammonia to form carbamates which, as solids, would quickly clog pipes and equipment. In the following process step, the carbon dioxide must therefore be removed from the gas mixture. In contrast to carbon monoxide, carbon dioxide can easily be removed from the gas mixture by gas scrubbing with triethanolamine. The gas mixture then also contains noble gases such as argon and methane, which are inert. [38]

        The gas mixture is then compressed to the required operating pressure by means of turbo compressors. The resulting compression heat is dissipated by means of heat exchangers and is used to preheat raw gases.

        The actual production of ammonia takes place in the ammonia reactor, whereby the first reactors burst under the high pressure, as the atomic hydrogen in the carbon-containing steel partially recombined to methane and produced cracks in the steel. That is why Bosch developed tubular reactors, consisting of a pressure-bearing steel tube in which a casing made of low-carbon iron was inserted, into which the catalyst was filled. Hydrogen diffusing through the inner steel tube escaped to the outside through thin bores in the outer steel jacket, the so-called Bosch holes. [40] The development of hydrogen-resistant chromium-molybdenum steels made it possible to construct single-walled tubes. A disadvantage of the tubular reactors was the relatively high pressure loss that had to be reapplied by compression. [46]

        Modern ammonia reactors are designed as floor reactors with low pressure loss, in which the contacts are distributed as beds on about ten floors one above the other. The gas mixture flows through them one after the other from top to bottom. Cold gas is injected from the side for cooling. A disadvantage of this type of reactor is the incomplete conversion of the cold gas mixture in the last catalyst bed. [46]

        Alternatively, the reaction mixture is cooled between the catalyst layers by means of heat exchangers, the hydrogen-nitrogen mixture being preheated to the reaction temperature. Reactors of this type have three catalyst beds. In addition to good temperature control, this type of reactor has the advantage of better conversion of the raw material gases compared to reactors with cold gas feed.

        The reaction product is continually removed for maximum yield. For this purpose, the gas mixture is cooled from 450 ° C in a heat exchanger using water, freshly supplied gases and other process streams. The ammonia also condenses and is separated in a pressure separator. The not yet converted reactants nitrogen and hydrogen are compressed again to reaction pressure by means of a circulating gas compressor, supplemented with fresh gas and fed to the reactor. [46] The ammonia is purified in a subsequent distillation.

        Most of the ammonia required annually is produced using the Haber-Bosch process. [47] Annual production was around 150 million tons in 2017, with China, India and Russia as the largest producers. [1] Due to the high energy requirements for the production of the pure hydrogen required, the Haber-Bosch process accounts for around 1.4 percent of the world's energy requirements. The resulting carbon dioxide emissions amount to around three to five percent of global emissions, some of which is used to generate urea. [48] ​​Nowadays, at least among the population of industrialized nations, around 40 percent of the nitrogen contained in the human body has already taken part in the Haber-Bosch synthesis. [49]

        About 80 percent of the primary product ammonia is processed into fertilizer, with other products accounting for 20 percent. The most important ammonia-based nitrogen fertilizers, in addition to the gaseous and aqueous solutions of ammonia, are ammonium nitrate and urea. [50]

        The production of urea in a high pressure process goes back to Carl Bosch and Wilhelm Meiser and was first put into operation by BASF in 1922. In 2010 the production volume was 130 million tons. [52] The entire world production of nitric acid occurs through catalytic combustion according to the Ostwald process. The process goes back to a lecture experiment in which a glowing platinum wire is immersed in an ammonia-air mixture to generate nitrous gases. [53] The world annual production was 80 million tons in 2009. [52] The most frequently produced by-product of nitric acid is ammonium nitrate. [52] Other secondary products such as potassium nitrate, phosphates partially or completely neutralized with ammonia such as mono-, di- and ammonium polyphosphates, ammonium sulfate and ammonium nitrate-urea solution are frequently used fertilizers. [54]

        About five percent of ammonia production is used to make explosives. [52] The nitro and nitrate groups found in many explosives are ultimately based on ammonia, which was obtained using the Haber-Bosch process, including important explosives such as trinitrotoluene and nitroglycerin. [55] About ten percent of ammonia production is used to make nitrogen-containing compounds such as nitriles, amines, and amides. [52] The range of secondary products is extremely diverse and ranges from urea resins, sulfonamides to nitrobenzene and its secondary product aniline in polyurethane and dye chemistry, caprolactam for the production of polymers and through to rocket fuels such as hydrazine. [56]

        Edit elementary steps

        The mechanism of ammonia synthesis is divided into the following seven steps:

        1. Transport of the starting materials from the gas phase through the boundary layer to the surface of the contact
        2. Pore ​​diffusion to the reaction center of the reactants
        3. Reaction of the products
        4. Return of the products through the pore system to the surface
        5. Return to the gas volume.

        Because of the shell structure of the catalyst, the first and last two steps are fast compared to adsorption, reaction and desorption. Exchange reactions between hydrogen and deuterium on Haber-Bosch catalysts take place at a measurable rate at temperatures of −196 ° C, and the exchange between deuterium and hydrogen on the ammonia molecule already takes place at room temperature. Since both steps are fast, they cannot determine the rate of ammonia synthesis. [57] It is known from various studies that the rate-limiting step in ammonia synthesis is the dissociation of nitrogen. [32]

        The adsorption of nitrogen on the catalyst surface depends not only on the reaction conditions but also on the microscopic structure of the catalyst surface. Iron has different crystal faces, the reactivity of which is very different. The Fe (111) and Fe (211) surfaces have by far the highest activity. The explanation for this is that only these surfaces have so-called C7 sites - these are iron atoms with seven closest neighbors. [32]

        The dissociative adsorption of nitrogen on the surface follows the following scheme, where S * means an iron atom on the surface of the catalyst: [4]

        N2 → S * -N2 (γ species) → S * -N2–S * (α species) → 2 S * –N (β species, Surface nitride)

        The adsorption of nitrogen is similar to the chemisorption of carbon monoxide.On an Fe (111) surface, the adsorption of nitrogen initially leads to an adsorbed γ-species with an adsorption energy of 24 kJmol −1 and an N-N stretching vibration of 2100 cm −1. Since nitrogen is isoelectronic with carbon monoxide, it adsorbs in an on-end configuration in which the molecule is bound via a nitrogen atom perpendicular to the metal surface. [58] [59] [32] This was confirmed by photoelectron spectroscopy. [60]

        Ab initio MO calculations have shown that in addition to the σ bonding of the lone pair of electrons of nitrogen to the metal, there is a π back bonding from the d orbitals of the metal into the π * orbitals of nitrogen, which represents the iron-nitrogen Bond strengthens. The nitrogen in the α state is more strongly bound at 31 kJmol −1. The resulting weakening of the N-N bond could be demonstrated experimentally by reducing the wave number of the N-N stretching vibration to 1490 cm −1. [59]

        Another warm-up of the Fe (111) face, which is caused by α-N2 is covered, leads to both desorption and the appearance of a new band at 450 cm −1. This represents a metal-N oscillation, the β-state. A comparison with the vibrational spectra of complex compounds allows the conclusion that the N2-Molecule is bound "side-on", with an N atom in contact at a C7 site. This structure is called "surface nitride". The surface nitride is very strongly bound to the surface. [60] Hydrogen atoms quickly add to this (Hads), which are very mobile on the catalyst surface.

        Surface imides (NHad), Surface amides (NH2, ad) and surface ammoniaates (NH3, ad), The latter decay under NH3-Delivery (desorption). [40] The individual molecules were identified or assigned using X-ray photoelectron spectroscopy (XPS), high-resolution electron energy loss spectroscopy (HREELS) and IR spectroscopy.

        On the basis of these experimental results, a reaction scheme can be created that consists of the following individual steps:

        As with every Haber-Bosch catalyst, the rate-determining step in ruthenium-activated carbon catalysts is nitrogen dissociation. The active center for this is a so-called B for ruthenium5Place, a 5-fold coordinated position on the Ru (0001) surface, at which two ruthenium atoms form a step edge with three ruthenium atoms of the Ru (0001) surface. [61] The number at B5-Position depends on the size and shape of the ruthenium particles, the ruthenium precursor and the amount of ruthenium used. [36] The reinforcing effect of the basic carrier has the same effect as the promoter effect of alkali metals, which is important here as well as with the iron catalyst. [36]

        Edit energy diagram

        With the knowledge of the reaction enthalpy of the individual steps, an energy diagram can be created. With the help of the energy diagram, homogeneous and heterogeneous reactions can be compared: Due to the high activation energy of the dissociation of nitrogen, the homogeneous gas phase reaction cannot be carried out. The catalyst avoids this problem, as the energy gain that results from the binding of nitrogen atoms to the catalyst surface overcompensates for the necessary dissociation energy, so that the reaction is ultimately exothermic. Nevertheless, the dissociative adsorption of nitrogen remains the rate-determining step: not because of the activation energy, but mainly because of the unfavorable pre-exponential factor of the rate constant. The hydrogenation is endothermic, but this energy can easily be applied by the reaction temperature (about 700 K). [32]

        Since the introduction of the Haber-Bosch process, the synthesis of ammonia from atmospheric nitrogen has become one of the world's most important chemical manufacturing processes. The development of process variants at the beginning of the 20th century often served to circumvent BASF's patent claims. Since the process requires significant energy consumption, later developments focused on energy efficiency. The average energy consumption per ton of ammonia in 2000 was around 37.4 GJ, while the thermodynamically determined minimum is 22.4 gigajoules per ton. [62]

        Casale method edit

        The Casale process was developed by Luigi Casale in the early 1920s. The process uses an iron catalyst, but works in contrast to the Haber-Bosch process with a pressure of around 800 to 1000 bar. [63] This made the reactor smaller and allowed good temperature control through an internal, central heat exchanger and the axial injection of cold gas. [64]

        The high operating pressure allowed the direct condensation of ammonia without absorption in water. By 1923 Casale had built 15 plants in Europe and the United States with a capacity of around 80,000 tons of ammonia per year; in 1927 the installed capacity was already 320,000 tons per year. [65] At that time, Casale was BASF's only competitor. In total, more than 200 ammonia plants based on the first generation of Casale technology have been built around the world. [65]

        Fauser method edit

        The Fauser process, named after the Italian electrical engineer Giacomo Fauser, largely corresponded to the Haber-Bosch process, but used the electrolysis of water as a hydrogen source. [66] The Fauser cell used 27% potassium hydroxide solution as the electrolyte and anodes and cathodes encased in asbestos, which ensured good separation of the gases produced. The process was introduced by Montecatini in the early 1920s. [67]

        Mont-Cenis Process

        The Mont Cenis process was developed by Friedrich Uhde and first put into operation in 1926 at the Mont Cenis colliery. The process, also known as the low-pressure process, works at pressures of 80 to 90 bar and a temperature of 430 ° C. The catalyst used was an iron cyanide-alumina catalyst, which was more active than the catalyst developed by Mittasch. The milder process conditions made it possible to use cheaper steels for the construction of the reactors. [68]

        Edit AMV procedure

        Imperial Chemical Industries developed the AMV process in 1982 with a highly active iron-cobalt catalyst that works at a reaction pressure of 100 bar and a temperature of 380 ° C. [69] Cobalt itself is hardly catalytically active, but serves to stabilize the contact through the formation of spinel phases with the aluminum oxide. In addition, when the contact is reduced, smaller iron crystallites of higher activity are formed. [70]

        A further development of the process is the LCA process (Leading Concept Ammonia) developed by ICI in 1988, which is designed for lower throughputs with the same energy input. The carbon dioxide, which is produced in a single-stage water-gas shift reaction, is removed by pressure swing adsorption. [71]

        Kellogg Advanced Ammonia Process Editing

        In 1992, M. W. Kellog developed a ruthenium-on-activated carbon catalyst that works at lower pressures and temperatures under the name Kellogg Advanced Ammonia Process (KAAP). [72] The pressure required is only about 40 bar due to the more active but expensive ruthenium catalyst. Alkali or alkaline earth metals such as cesium and barium are used as promoters. [73] The catalyst is said to be about 10 to 20 times as active as the conventional iron catalyst.

        Solid State Ammonia Synthesis Process Edit

        In the solid-state ammonia synthesis process (SSAS process, solid-state ammonia synthesis process), the direct electrolytic synthesis of ammonia from water and nitrogen using electrical energy bypasses the detour via hydrogen production from water. [74] This increases the efficiency. The formation of ammonia takes place electrochemically according to the following equation:

        The gross equation of the reaction is:

        Since ammonia is a high-energy substance, a lot of electrical energy is required. This process is therefore only economical if very cheap electrical energy is available.


        Applications and meaning

        The saturation vapor pressure is a measure of the proportion of those molecules or atoms that have enough energy to overcome the short-range and long-range order (the cohesive forces and the surface tension) and switch to the gaseous phase. The probability for this is given by the Boltzmann statistics. Therefore the vapor pressure curve is proportional to the Boltzmann factor:

        where $ Q_d $ is the evaporation energy of a molecule or atom.

        It follows from this that in the state of equilibrium the number of particles in a specific gas volume is greater at higher temperatures than at lower temperatures, which also means that the particle density increases with the temperature.

        Important examples are water vapor and humidity. Many humidity measures are defined or calculated using vapor pressure and saturation vapor pressure, especially in connection with the relative humidity, the saturation deficit and the dew point.

        One example of an application of saturation vapor pressure in technology is freeze-drying, another is pressure cooking (see pressure cooker). In building physics, the Glaser method (a comparison of saturated steam pressures according to the temperature profile and the theoretically prevailing partial steam pressures at the layer boundaries of the component) is used to assess whether a planned component is at risk from condensation.


        Table of contents

        Evidence for the use of iron in the various cultures through archaeological finds is relatively rare compared to the findings of bronze. On the one hand, iron was used only to a limited extent in the oldest periods of history, on the other hand, iron tends to corrode in humid air, in water and in wet earth, which means that many objects are not preserved. Only special circumstances or large dimensions of the object prevented the loss of such pieces. [14]

        Word origin

        In the past it was assumed that the Celtic and Germanic word for iron (Celtic *isarnon, Germanic *isarna) was borrowed from Illyrian. Also because of the contrast to the softer bronze, a relationship of *isarnon too latin ira "Anger, violence" represented. [15] [16] The New High German word iron (from Middle High German īsen, and to īsīn "Iron") becomes over Old High German īsa (r) n, from ancient Germanic *īsarnan, and this one from Gallic *īsarnon derived from an Illyrian origin, on the other hand, is now considered unlikely. [17] *isarnan and isarnon sit down except in German iron also in the other Germanic languages ​​(English iron, North Frisian joorn, West Frisian izer, Dutch IJzer) and in Celtic languages ​​(Breton houarn, kymr. haearn, Irish and Scottish Gaelic iarann, Manx yiarn).

        In addition to its outstanding importance as a material, iron was used in alchemy, where it was associated with the symbol "♂" for the planet Mars and for masculinity. [18]

        Earliest use of meteorite iron

        Before people in the various cultures learned to extract iron from ore, they used the meteor iron known before the actual "Iron Age" and recognizable by its specific nickel content of around 5 to 18%, or else Meteorite iron. Due to its rarity, this "sky iron" (ancient Egyptian: bj-n-pt = "iron of heaven" [19]) was correspondingly valuable and was mainly processed into cult objects and jewelry. In ancient Egypt, for example, ornamental pearls made of meteor iron with a nickel content of approx. 7.5% were found in two graves from pre-dynastic times, [20] which date back to around 3200 BC. Are dated. [21] It was also possible to confirm the assumption made early on that a dagger found on the mummy of Pharaoh Tutankhamun was made from meteor iron. The oldest known finds from meteors come from Mesopotamia, which the Sumerians living there called "urudu-an-bar" (= Copper of heaven) was designated. Among other things, a dagger with a blade made of meteor iron (10.8% Ni) and a gold-coated handle was discovered in the city of Ur, the manufacture of which dates back to around 3100 BC. Is dated. [23]

        Iron production from ore

        For the beginnings of iron smelting see

        Mediterranean and Asia Minor

        The use of nickel-free, i.e. terrestrial iron must also have taken place early in Mesopotamia, as evidenced by a nickel-free iron dagger with a bronze handle from the period between 3000 and 2700 BC. BC, which was found in the ruins of Ešnunna near Tell Asmar in what is now Iraq. [23] From the records of the Hittites in the archives of Boğazkale (formerly Boğazköy) in Central Anatolia it emerges that iron was already known at the time of King Anitta (approx. 1800 BC) and that iron has been smelting since at least approx. 1300 BC. Chr. [24] Between 1600 and 1200 BC Iron production remained largely a monopoly of the Hittite Empire and was a factor in its rise. From 1200 BC In the Levant, steel was produced by increasing the carbon content. [25] The Hittites used the iron, which was initially weighed up to eight times its weight in gold, [25] mainly for jewelry. [26] In the late Hittite period, iron was so common that it was no longer listed in inventory lists with the precious metals, but together with copper. However, there can be no question of a monopoly of the Hittites: Unique pieces made of terrestrial iron from the Middle and Late Bronze Age were also found in Greece and Cyprus, in Jordan, Lebanon, Israel and Egypt. [14]

        The Iron Age is generally believed to have started in the Middle East around 1200 BC. BC - not because iron played a significant role from this point on, but because the cultures of the Bronze Age collapsed within a very short time. The first centuries of the Iron Age are a "dark age" in this region, in which many cities were destroyed, long-distance trade collapsed and metal production almost fell asleep. Only from around 700 BC When cultures recovered from collapse, iron became more common again. Since 1200 BC In this region there is also known Damascus steel or melted damask, named after the city of Damascus, which has a very high carbon content of around 1.5% and a characteristic pattern when polished. However, this material is not only known in the Middle East, but also earlier in other regions, for example in South India, where it has been used since 300 BC at the latest. Is manufactured. [14]

        In ancient Egypt, iron was only smelted in the 6th century BC. Proven. Meteorite irons have been used since the Old Kingdom. This was referred to in later texts as bj-n-pt ("Iron of Heaven") and mainly used for the production of amulets and model tools for the mouth opening ritual. [27] A well-known find is a dagger blade as a burial gift from Tutankhamun from around 1350 BC. BC, which, according to recent studies, very likely consists of meteoric iron. Another iron find in a grave near Abydos from the 6th dynasty (2347-2216 BC) could be determined as nickel-free and thus of terrestrial origin, but its earlier use could not be determined because the piece rusted completely was. [20] An iron knife found in the joints of the Great Pyramid in 1837, which was initially dated to the 4th Dynasty, [28] turned out to be a modern piece. [29]

        Furthermore, the Chalyber belonged to the peoples of the Mediterranean and Asia Minor who had already gained a good knowledge of the use of iron as a metallurgical material. Her name lived in the Greek word for steel (chalybs) further, in contrast to ordinary iron (sideros). [30] The earliest traces of iron smelting on Greek territory were found in the form of iron slag from around 2000 BC. In Agia Triada on Crete. [31]

        In ancient Egypt and in Gerar (Palestine), iron smelting began around 1000 BC. Known for Gerar (evidenced by iron smelting furnaces and locally produced agricultural implements [30]) and in China at least since the Han dynasty (206 BC to 222 AD) [32].

        Europe

        The iron tents and spears that Count Gozzadini discovered in Etruscan tombs near Bologna in 1853 are among the oldest European pieces. They date from the 9th to 10th centuries BC. [33] In Central Europe in general, the pre-Roman Iron Age is usually divided into the Hallstatt Period (800-450 BC) and the Latène Period (from 450 BC), with the first iron objects having appeared as early as the Late Bronze Age. [14]

        One of the oldest known iron finds in Germany is an iron rivet as a connection between a bronze lance tip and a wooden shaft, which was found in Helle (Ostprignitz) and dates from around 800 BC. BC. [30] In German-speaking countries, however, the La Tène period, which only began about 300 years later in the entire Celtic culture, marked a first high culture with numerous iron smelting sites and iron finds (e.g. in Siegerland and Teltow).[14] [34] In northern Germany, the Bronze Age cultures persisted in the Hallstatt Period. South of the Alps, on the other hand, there was a high culture, the Etruscans, who produced large quantities of bronze and iron and whose products also reached Central Europe. Among other things, they mined an iron skarn on Elba. [14]

        Racing furnaces or racing works with associated forges were widespread in Europe until the 18th century. Until the late Middle Ages, they were the only way to make malleable iron. From this point on, “freshening” allowed the carbon content of the raw or cast iron to be reduced. [14] Liquid pig iron was not created with this process, however, since a racing furnace could only reach temperatures between 1000 and 1200 ° C, but the melting point of pure iron is 1538 ° C (melting point of pure cementite, Fe3C: 1250 ° C). The development of blast furnaces and thus cast iron did not take place until later in Europe. The earliest pieces of cast iron were discovered in Sweden (Lapphyttan and Vinarhyttan) and dated to 1150-1300. [35] With the cast cannonball (from 1400 [36]), cast iron processing spread like the campaigns across Europe.

        When the dwindling forests in Europe could no longer meet the growing need for charcoal for iron production, alternatives were sought. In 1709, Abraham Darby in Great Britain was the first to use coal (more precisely the coal product coke) as an alternative. In Germany it was not possible to operate a blast furnace with coke until 1796. [37] This change, together with the invention of the steam engine, is considered to be the beginning of the industrial revolution. The smelting works produced cast iron and wrought iron. With the introduction of the puddling process around 1784, it was possible to replace the previously common charcoal with the cheaper hard coal. [14]

        Iron use and finds outside Europe and Asia Minor

        There was also a very old tradition of iron production in Africa, which began around 3000 years ago. The African metallurgists were very eager to experiment and innovative, the construction methods and shapes of the furnaces show a variety that cannot be found on other continents. With a few exceptions - namely Mauritania and Niger - there was no Copper or Bronze Age at most of the sites south of the Sahara that preceded iron smelting: the Neolithic was immediately followed by the Iron Age. Archaeologists dated the oldest known smelting furnace in Africa, which was discovered in the Termite massif in Niger, to 800 BC. Other sites for iron processing were discovered, for example, in Walalde in Senegal, in the Central African Republic, in Rwanda, in Taruga, the region around Nsukka and on the northern edge of the Mandara Mountains in the border area between Nigeria and Cameroon. [14]

        From the 7th century BC In addition to the cultures in the Middle East and parts of Europe, iron was also known in many other regions: for example in India and Sri Lanka, in China, in Eastern Europe with the Scythians and also south of the Sahara in Africa. Colchis, today's western Georgia, was an important iron producer in the 7th century. About 400 ovens have been found there in which hematite and magnetite were smelted. [14]

        In China, the first experience with iron was gained from meteorite iron. The first archaeological traces of wrought iron can be found in the northwest, near Xinjiang, from the 8th century BC. It is believed that these products, created using Middle Eastern methods, came to China through trade. That changed in the late Zhou period in the 5th century BC. With a massive production of cast iron in blast furnaces. China continuously developed the technology and remained a very innovative center of metallurgy. [14]

        Iron objects and larger iron stores in the ruins of Khorsabad were found in the tombs of Turan, a region that stretched across eastern Iran, southern Afghanistan and southwest Pakistan. Victor Place discovered rings and chain parts together with around 160,000 kg of iron bars. [38] Layard came across iron weapons such as helmets, spears and daggers during his excavations in Nimrud. [39] Famous is the Iron Column in Delhi, a seven-meter-high wrought-iron pillar from the 4th and 5th centuries. Century. [40]

        In Australia and the surrounding populated islands of Polynesia, however, the use of iron was unknown until it was discovered by European researchers. Even in the otherwise high-standing culture of the Incas and Aztecs of Central and South America, gold, silver, copper and bronze of good quality and great craftsmanship were processed, but iron only in small quantities and only meteoric iron. [41]

        Iron is in line with the relative abundance of elements related to silicon in the universe with 8.7 · 10 5 atoms per 1 · 10 6 silicon atoms in 9th position. [42] The fusion of elements in stars ends with iron, since during the fusion of higher elements no more energy is released, but has to be expended (see nucleosynthesis). Heavier elements are created endothermically in supernova explosions, which are also responsible for the scattering of the matter created in the star. [43]

        Iron is in line with the Element abundance according to the mass fraction in 2nd place in the entire earth (28.8% [44]), in 4th place in the earth's envelope (4.70% [1]) and in 4th place in the continental crust (5.63% [45 ]) Seawater only contains 0.002 mg / L [10]. Iron, along with nickel, is probably the main component of the earth's core. Presumably driven by thermal forces, convection currents of liquid iron in the outer core create the earth's magnetic field. [46]

        Most of the iron in the earth's crust is associated with various other elements and forms several hundred different iron minerals. [47] An important and economically significant class are the iron oxide minerals such as hematite (Fe2O3), Magnetite (Fe3O4) and siderite (FeCO3), Limonite (Fe2O3· N H2O) and goethite (FeO · OH), which are the main ores of iron. [48] ​​Many igneous rocks also contain the sulfide mineral pyrrhotite and the nickel-iron mineral pentlandite, which is intergrown with it. [49] During weathering, iron tends to dissolve out of sulfide deposits as sulfate and from silicate deposits as hydrogen carbonate. Both are oxidized in aqueous solution and precipitate in the form of iron (III) oxide at a slightly increased pH. [50]

        Large iron deposits are ribbon ores, a type of rock made up of repeated thin layers of iron oxides alternating with ribbons of low-iron shale and chert. The ribbon ores were mainly deposited between 3700 million years ago and 1800 million years ago (the most recent were formed 350 million years ago) by the reaction of iron with the oxygen produced by cyanobacterial photosynthesis. [51]

        Materials that contain finely ground iron (III) oxides or oxide hydroxides such as ocher have been used as yellow (ocher), red (hematite), brown (umber) and black (magnetite) pigments since prehistoric times. [52] They also contribute to the color of various rocks and clays, including entire geological formations such as the Painted Hills in Oregon [53] and the red sandstone [54]. Iron sandstone in Germany and Bath Stone in Great Britain make iron compounds responsible for the yellowish color of many historical buildings and sculptures. The proverbial red color of the surface of Mars comes from a regolith rich in iron oxide. [55]

        In the iron sulfide mineral pyrite (FeS2) contain considerable amounts of iron. However, it is mainly used for the production of sulfuric acid, whereby the gravel burns that occur during production have a high iron content. [56] However, it is only possible to use these for iron extraction with modern methods, since residues of the sulfur have to be removed, which make the iron brittle. [57] In fact, iron is so widespread that production generally focuses only on ores with a very high iron content. [52]

        Iron in ores

        The first deposits to be mined were turf iron stone and exposed ores. Today magnetite (Fe3O4), Hematite and siderite mined. The largest iron ore deposits are found in the so-called Banded Iron Formations (BIF, banded iron ore or band ore), which are also known as taconite or itabirite and contain iron mainly in the minerals hematite and magnetite. [58]

        Iron as a mineral

        Iron is rarely found in nature, mostly in the form of small bubbles or thickenings in the surrounding rock, but also as massive mineral aggregates weighing up to 25 t, [59] and is therefore recognized as a mineral. The International Mineralogical Association (IMA) lists it according to the systematics of minerals according to Strunz (9th edition) under the system no. "1.AE.05" (elements - metals and intermetallic compounds - iron-chromium family) [60] (8th edition: I / A.07-10). The systematics of minerals according to Dana, which is also common in English-speaking countries, lists the element mineral under system no. "1.1.11.0".

        So far, solid iron has been detected at 120 sites worldwide (as of 2010), although the vast majority consists of meteoritic iron finds of the Kamacite variety. [61]

        Iron crystallizes in the cubic crystal system, has a Mohs hardness between 4 and 5 [62] and a steel-gray to black color, depending on the formation conditions and degree of purity (Iron black [63]). The line color is also gray.

        Because of the reaction with water and oxygen (rusting), solid iron is not stable. It therefore occurs in an alloy with nickel either as kamacite (4 to 7.5% Ni) or taenite (20 to 50% Ni) only in iron meteorites and in basalts, in which iron-containing minerals are sometimes reduced. Iron with lower nickel contents are considered a variety of the same and are under the designation Josephinite known, [64] however this name is also a synonym for the mineral Awaruit (Ni3Fe) [65].

        Iron ores, on the other hand, are found comparatively often, important examples are the minerals magnetite (Magnetic iron stone, Fe3O4), Hematite (Roteisenstein, Fe2O3), Pyrrhotine (Magnetic gravel, FeS), pyrite (Iron gravel, FeS2), Siderite (Iron spar, FeCO3) and limonite, which is considered to be rock (Brown iron stone, Fe2O3· N H2O). The sedimentary rock Iron oolite, sometimes as Eisenstein called, consists of iron hydroxide minerals, cemented with clayey or calcareous binders. The minerals chlorite, glauconite and pyrite are of less industrial interest, but are found fairly frequently in nature. A total of 1424 iron minerals are currently (as of 2010) known. [66]

        Iron in foods

        Many foods contain traces of iron. For example, oats (dehulled) contain 58 mg / kg, barley (dehulled) and rye 28 mg / kg, wheat 33 mg / kg, cocoa (slightly de-oiled) 125 mg / kg, spinach 38 mg / kg, potatoes 5 mg / kg, Parsley 55 mg / kg, apple 2 to 9 mg / kg, beef 21 mg / kg, beef liver 70 mg / kg, beef kidney 11 mg / kg, pig liver 154 mg / kg, pork 18 mg / kg, pig kidney 100 mg / kg, Pig blood 550 mg / l, bovine blood 500 mg / l, cow's milk 0.5 mg / l and egg yolk 60 to 120 mg / l. [67]

        With 711 million tons (60 percent), the People's Republic of China is by far the most important producer country for pig iron in 2017, followed by Japan 78 million tons (6.6 percent), India 66 million tons (5.6 percent) and Russia 52 million Tons (4.4 percent). The four states together had a share of 77.5 percent in the world production of 1170 million tons. In Europe, other important producers were the Ukraine, Germany and France. [68]

        Around 2.4 billion tons of iron ore were mined worldwide in 2017. The most important iron ore suppliers were Australia, followed by Brazil, the People's Republic of China, India and Russia. Together they had a share of 80.8 percent of world production. In addition, new iron is made from scrap. [69]

        The largest pig iron producers worldwide (2016)
        rank country production
        (in million t)
        rank country production
        (in million t)
        1 People's Republic of China 700,7 11 Taiwan 0 14,9
        2 Japan 0 80,2 12 Turkey 0 12,5
        3 India 0 77,3 13 France 0 0 9,7
        4 Russia 0 51,9 14 Canada 0 0 7,6
        5 South Korea 0 46,3 15 United Kingdom 0 0 6,1
        6 Brazil 0 35,0 16 Netherlands 0 0 6,1
        7 Germany 0 27,3 17 Italy 0 0 6,0
        8 United States 0 22,3 18 Austria 0 0 5,6
        9 Ukraine 0 21,9 19 Mexico 0 0 5,2
        10 Iran 0 18,3 20 South Africa 0 0 5,0

        Development of global iron ore production (in million tons) [70]

        Development of worldwide pig iron production (in million tons) [71]

        Ore mining and processing

        Iron ore is mainly extracted in open-cast mining and less often in civil engineering (underground mining, as in the Kiruna iron ore mine). Where the iron ore deposits recognized as being worthy of mining are openly exposed, the ore can be extracted in less laborious open-cast mining. Most of the iron ore is mined in Brazil, Australia, China, India, the United States and Russia. [72] [73]

        In recent years, these countries have displaced the originally most important iron ore producing countries such as France, Sweden and Germany, whose last iron ore mine in Upper Palatinate was closed in 1987. [74] [75]

        For technological and economic reasons, the ores used for processing in blast furnaces should have uniform properties from a chemical and physical point of view. Accordingly, the coarse ores obtained during mining have to be broken, ground and sieved and the ores that are too fine have to be made lumpy. This is known as ore preparation. Irregularities in the ores of one or different mining sites are compensated for by mixing the ores on so-called mixed beds. Only a small part of the ores can be used directly in the blast furnace as lump ore. [76] The main part of the iron ore is present as fine ore and must be made lumpy for use in the blast furnace, since the fine ore would greatly impair or even prevent the air supply (wind) in the blast furnace. [77] The most important processes for this are sintering and pelleting. In Germany, the ores are mainly made into pieces by sintering. In other countries, for example in the USA, more pellets are used, whereby the grain size resulting from the processing is decisive for the selection of the process. Sintering requires a grain size of more than 2 mm, while ores that are even more finely ground are pelletized. [76]

        In the sintering plants, coarser ore grains are sorted and sintered according to their size. Small ore grains have to be placed together with lime aggregates on gas-fired, motor-driven traveling grids (grate conveyor belts) and melted by intense heating and thereby "baked" (sintered). Very fine ore is ground into a fine powder, which is often necessary to separate gangue. Then it is intensively mixed with limestone, fine-grain coke (coke breeze) and water and placed on a motor-driven traveling grate. Gases are extracted from below through the traveling grate. It is lit from above and a burning front moves from top to bottom through the mixture, which is briefly melted (sintered). When pelleting, a mixture is created with binding agents, aggregates and water, which is then rolled onto pelletizing plates to form small balls (green pellets) with a diameter of 8 to 18 mm [78]. These are burned into pellets with gas firing at 1000 ° C on a traveling grate, in shaft ovens or rotary kilns. Sinter is not easy to transport and is therefore produced in the iron and steel works, pellet plants are mostly operated near the ore mines. [77] [76]

        Iron production in the blast furnace

        The iron is obtained by chemical reduction of the iron oxide of the oxidic iron ores (or sulfidic iron ores after their roasting with atmospheric oxygen) and carbon (coke). Pig iron is produced almost exclusively in tall blower shaft furnaces (blast furnaces). Only in countries with cheap hydropower plants and expensive coal does generation in electric ovens play a limited role. Coke and ore are poured into the furnace alternately in layers at the top of the furnace. [79] For this purpose, two bunkers are usually arranged above the furnace vessel, which serve as gas locks between the furnace vessel and the environment. At the very top there is a rotary chute within the furnace vessel, with which the material is distributed in a spiral shape over the loading surface. The layers of coke in the lower area of ​​the furnace, when the ore becomes plastic, maintain that process gas can flow through the bed (coke window). [80]

        The insert sinks in the furnace shaft and is dried, heated, the iron oxides reduced and finally melted (redox reaction) by the rising process gas, which is about 1600 to 2200 ° C (at the injection point) and consists of carbon monoxide and nitrogen. The process gas is generated by blowing air preheated to around 900 to 1300 ° C into the furnace using blow molding (water-cooled copper nozzles [81]). The oxygen in the air burns with coke to form carbon monoxide. The entire process takes about eight hours. [79]

        The so-called “indirect reduction” takes place in the temperature zone between 500 and 900 ° C. The various iron oxides react with carbon monoxide or hydrogen in three stages until metallic iron is finally present: [79]

        The more ferrous magnetite is formed from hematite.

        Metallic iron is made from wüstite and accumulates in the blast furnace below.

        In the temperature range from 900 to 1600 ° C, a "direct reduction" with carbon also takes place: [79]

        The top gas coming from the blast furnace is freed from the dust and is used to operate the wind heaters, fans, pumps, lighting, gas cleaning and transport devices required for the blast furnace process. The surplus is used for steel mill operations or other industrial purposes. [79]

        In addition to liquid iron, the furnace also produces liquid slag. Since the melting point of a mixture of SiO2 and Al2O3 is too high to form a slag that is liquid at 1450 ° C, aggregates are used to produce more easily meltable calcium aluminum silicates to lower the melting point. Is it z. B. to alumina and silicic acid-containing gangues, which is usually the case, one suggests accordingly calcareous, d. H. basic components (e.g. limestone, dolomite). In the case of calcareous gaits, conversely, alumina and silicic acid-containing, i.e. H. acidic aggregates (e.g. feldspar, clay slate) are added. The iron and the slag are mixed together in the blast furnace, have a temperature of about 1450 ° C and are drawn off through a tap hole that is opened about every two hours by drilling and closed after about an hour by plugging with a ceramic mass. Iron and slag are separated outside the furnace. The iron is filled into transport pans and brought to the steelworks. [79] [82]

        The iron is liquid at 1450 ° C because the carbon dissolved in the iron lowers the melting point. The slag is atomized with water. It solidifies as a fine-grained glass (slag sand) due to the quenching. This slag sand is finely ground and used as a concrete additive (filler). During the entire manufacturing process, depending on the process in the blast furnace, between 200 [83] and 1000 kg of slag [84] are produced per ton of iron.

        Ore and coke contain silicon dioxide (quartz sand, silicates) SiO as the main impurity2 and aluminum oxide Al2O3. A small part of the silica is reduced to silicon, which is dissolved in the iron. The remainder, together with the aluminum oxide, forms the slag (calcium aluminum silicates [79]).

        The iron in the blast furnace (pig iron) only has an iron content of around 95%. It contains 0.5 to 6% manganese, as well as too much carbon (2.5 to 4%), sulfur (0.01 to 0.05%), silicon (0.5 to 3%) and phosphorus for most applications (0 to 2%). [79] In the steelworks, therefore, desulphurisation is usually first performed by blowing in calcium carbide, magnesium or quicklime, whereby optimal desulphurisation is a prerequisite for the production of spheroidal graphite cast iron. [85] If pig iron is cooled very slowly, e.g. B. in sand molds (“ingot beds”), the dissolved carbon separates out as graphite and “gray pig iron” is obtained (gray fracture surface, melting temperature approx. 1200 ° C). Another condition for this is that the silicon content predominates over the manganese content (> 2% Si <0.2% Mn). With faster cooling, z. B. in iron shells ("chill molds"), the carbon remains as iron carbide in the pig iron, so that a "white pig iron" (white fracture surface, melting temperature around 1100 ° C, is mainly used to manufacture steel). A predominance of the manganese content (<0.5% Si & gt 4% Mn) is also essential here, which counteracts the precipitation of graphite. [79]

        Iron production without a blast furnace

        Blast furnaces have a large material and energy requirement, which cannot always be provided if the raw material and energy conditions are unfavorable. Because of this, and because of environmental concerns, alternative methods of processing iron have been developed. In these, the existing iron ores are to be reduced with little or no use of coke or, alternatively, with hard coal, lignite, crude oil or natural gas. In the majority of the processes referred to as "direct iron reduction", the pig iron produced is obtained in solid, porous form, which is referred to as sponge iron or "direct" iron and is suitable for steel production.

        Two main reactions include the direct reduction process: When using methane (natural gas) and oxygen (alternatively water vapor or carbon dioxide) this is partially oxidized (with heat and a catalyst): [86]

        The iron ore is then treated with these gases in a furnace, resulting in solid sponge iron:

        Silica is removed by adding a limestone flux as described above. [87]

        Well-known direct reduction processes, sorted according to the respective reduction vessel, include: [88]

        1. Iron production in the shaft furnace:
            , developed around 1918 in Sweden, developed in the Oberhausen / Midrex process, developed by the Midland Ross Corporation in Cleveland, Ohio
        2. All three processes use a more or less short shaft furnace and, as input materials, iron-rich lump ores, sinter or pellets, which are preheated and placed at the furnace head. A 1000 ° C reducing gas mixture of carbon monoxide (CO), hydrogen (H.2), Carbon dioxide (CO2), Water (H.2O) and possibly methane (CH4) blown in. The sponge iron produced has a purity of 85 to 95%.
            -Procedure
    • Iron production in the retort:
        , developed in 1908 by E. Sieurin in Höganäs, Sweden, developed by the company in 1957 Hojalata-y-L.amina S.A. in Monterry, Mexico
    • Very rich iron ore concentrates are placed in ceramic retorts or muffles and reduced either with fine-grain coal, coke breeze and limestone or with natural gas. The sponge iron produced has a purity of 80 to 95% and is used either for the production of special steels or as iron powder for powder metallurgy.
  • Iron production in a rotating vessel: developed by the R.epublic Steel Corporation and the National Lead Corporation developed by the S.teel Company of Canada and the L.urgi Society for Chemistry and Metallurgy
  • Lump ore or pellets are introduced here together with limestone or dolomite in rotary kilns up to 110 m long, which are heated to up to 1050 ° C with lignite, coke oven gas or heating oil. Sponge iron is produced with a purity of 85 to over 90%.
      (Domnarf reduction process), developed at Stora Kopparbergs bergslag in Sweden
    Preheated iron ore is brought into a rotary kiln with coal or coke on a pig iron sump. By blowing in pure oxygen, the carbon monoxide contained in the reducing gas is burned to carbon dioxide and the rotary kiln is heated to approx. 1300 to 1350 ° C. Liquid pig iron is produced.
  • Iron production in the fluidized bed reactor
      , developed by Hydrocarbon Research Inc. (USA) (Fluid Iron Ore Reduction), developed by Standard Oil Company, New York
  • Sponge iron is produced from fine-grain iron ores, which are whirled up and reduced either with injected hydrogen, natural gas or refinery residual gas.
      -Procedure
  • Iron production in an electric furnace
    • The Tysland Hole process and the Demag process manage without preheating and pre-reduction of the input materials. and Strategic Udy processes, on the other hand, require preheating and pre-reduction of the ore using rotary kilns.
    However, iron production in electric furnaces is only worthwhile if electricity can be provided in sufficient quantities and at low cost. Depending on the quality of the iron ore and carbon carriers, the energy consumption is between 2000 and 2500 kWh per ton of pig iron.
  • Thermite reaction

    The ignition of a mixture of aluminum powder and iron (III) oxide produces liquid metallic iron via the thermite reaction:

    The reaction is of no importance for the production of iron from ore, among other things because the aluminum required requires a considerable amount of electrical energy for its production. The aluminothermic welding uses the remaining energy of the liquid iron after the reduction of the iron oxide by means of aluminum for fusion welding, among other things. of railroad tracks.

    Steel production

    In γ-iron, carbon is soluble up to a maximum of 2.06%, steel contains 0 to 2% carbon, it can be forged and rolled, but it can only be hardened from 0.5% carbon. If the value is lower, it is non-hardenable steel or wrought iron. [89]

    Various processes have been developed for making steel, including puddle furnaces, Bessemer converters, open hearth furnaces, oxygen-based furnaces and electric arc furnaces. In all cases the goal is to oxidize some or all of the carbon along with other impurities. On the other hand, other metals can be added to make alloy steels. [79]

    Depending on the process, any desulphurisation slag that may have arisen is drawn off or tapped, and the pig iron is then used to produce steel in a converter (oxygen blowing process, wind-freshening process such as the Thomas process, stove-freshening process such as the Siemens-Martin process) with the addition of quicklime and blowing in air or blow oxygen in an oxidizing manner. Silicon is burned to silicon dioxide and carbon to carbon dioxide. The phosphorus is bound as calcium phosphate. The liquid iron then has a temperature of around 1600 ° C. It contains so much oxygen that carbon monoxide bubbles form from remaining carbon when it solidifies. This is undesirable in the continuous casting that is most commonly used today. When the steel is tapped from the converter into the ladle, aluminum is therefore added to bind the oxygen as aluminum oxide. If the quality of the steel is high, the converter process is followed by further process steps, such as: B. a vacuum treatment (secondary metallurgy). [79]

    Alternatively, pig iron can also be processed into steel (with up to 2% carbon) by cementation using other methods such as the puddling process or tempering, as well as wrought iron (commercially available pure iron). [79]

    Physical Properties

    Chemically pure iron is a silver-white, relatively soft, ductile, very reactive metal with a density of 7.873 g / cm 3, which melts at 1535 ° C and boils at 3070 ° C. [79]

    The average iron atom has about 56 times the mass of a hydrogen atom. The atomic nucleus of the iron isotope 56 Fe has one of the largest mass defects and thus one of the highest binding energies per nucleon of all atomic nuclei. That is why it is considered to be the final stage in the production of energy by nuclear fusion in the stars. However, the absolute highest mass defect has 62 Ni, followed by 58 Fe, and only in third place does 56 Fe follow. [90] [91]

    At room temperature, the allotropic modification of pure iron is ferrite or α-iron. This modification crystallizes in a body-centered cubic crystal structure (tungsten type) in the space group in the 3 m (Space group no. 229) Template: Space group / 229 with the lattice parameter a = 286.6 pm and two formula units per unit cell. This modification is stable below 910 ° C. Above this temperature it changes into the γ-modification or austenite. This has a face-centered cubic structure (copper type) with the space group Fm 3 m (No. 225) Template: Space group / 225 and the lattice parameter a = 364.7 pm. A third structural change takes place at 1390 ° C, above this temperature up to the melting point at 1535 ° C, the body-centered cubic δ-ferrite is stable again. [92] Phase transitions also take place at high pressure: at pressures of more than about 10 to 15 GPa and temperatures of at most a few hundred degrees Celsius, α-iron is converted into ε-iron, the crystal lattice of which is a hexagonal closest packing of spheres (hcp), At higher temperatures up to the melting point, a corresponding conversion of γ-iron to ε-iron takes place, the pressure of the phase transition increasing with temperature. In addition, there may be another phase transition from ε-iron to β-iron, which is around 50 GPa and more than 1500 K, but the existence of this β phase is controversial, and there are also various findings on its crystal structure, among others. an orthorhombic or a double hcp structure. [93] These transformations are also called the "polymorphism of iron". [6]

    The lack of a β-phase in the standard nomenclature of the iron allotropes stems from the fact that it was previously assumed that the change in magnetism at the Curie point at 766 ° C from ferro- to paramagnetism is accompanied by a structural change and thus a further modification between 766 and 910 ° C exists, which has been referred to as β-modification or β-iron. However, after more precise measurements, this turned out to be wrong. [79]

    The solubility of carbon in α-iron is very low and is a maximum of 0.018% at 738 ° C, as can be seen from the iron-carbon diagram. Much more carbon (up to 2.1% at 1153 ° C) can dissolve in γ-iron. In molten iron, the solubility of carbon at 1153 ° C is about 4.3%, although this increases with increasing temperature. [79]

    The melting point of iron is only well determined experimentally for pressures of up to about 50 GPa. At higher pressures, different experimental techniques give very different results. Various studies localize the γ-ε triple point at pressures that differ by several dozen gigapascals, and are 1000 K and more apart at the melting temperatures under high pressure. In general, molecular dynamic model calculations and shock experiments result in higher temperatures and steeper melting curves than static experiments in diamond anvil cells. [94]

    The spectrum of iron shows spectral lines in all spectral ranges. [95] In astronomy, more precisely in X-ray astronomy, the strong emission lines of neutral iron in the X-ray range are of great interest. Astronomers observe them in active galactic nuclei, X-ray binary stars, supernovae and black holes. [96]

    Magnetic properties

    As a transition metal, iron has a permanent magnetic moment in every atom. [98] Below its Curie point of 770 ° C, α-iron changes from paramagnetic to ferromagnetic: the spins of the two unpaired electrons in each atom generally align with the spins of its neighbors, creating an overall magnetic field. [99] This happens because the orbitals of these two electrons (i.e.z 2 and dx 2 − y 2 ) do not point to neighboring atoms in the lattice and are therefore not involved in the metal bond. [100]

    In the absence of an external magnetic field source, the atoms are spontaneously divided into magnetic domains with a diameter of about 10 micrometers, [101]. These are crystal areas delimited by Bloch walls (Weiss districts). Because of the random orientation of these magnetic domains, no moment can be felt externally. Thus, a macroscopic piece of iron has a total magnetic field close to zero. [98]

    Another possibility is the anti-parallel arrangement of the moments in iron alloys below the Néel temperature T.N dar (antiferromagnetism). Here the moments are already compensated on an atomic level. While in the para- and antiferromagnetic state no noteworthy polarization can be achieved through the usual external magnetic fields, in the ferromagnetic state this can be achieved very easily by migrating the Bloch walls and rotating the polarization direction of the domains. [98]

    The application of an external magnetic field causes domains magnetized in the same general direction to grow at the expense of neighboring domains facing in other directions, thereby increasing the external field. This effect is used in electrical devices that have to channel magnetic fields, such as. B. electrical transformers, magnetic recording heads and electric motors. Impurities, lattice defects or grain and particle boundaries can "fix" the domains at the new positions, so that the effect remains even after the external field has been removed and the iron object thus becomes a permanent magnet. [99]

    Some iron compounds, such as ferrites and the mineral magnetite, a crystalline form of mixed iron (II, III) oxide, show a similar behavior (although the atomic mechanism, ferrimagnetism, is somewhat different). Magnetite pieces with natural permanent magnetization (magnetic iron stones) were the earliest compasses for navigation. Magnetite particles were used extensively in magnetic recording media such as core memories, magnetic tapes, floppy disks and disks until they were replaced by cobalt-based material.

    Chemical properties

    Oxidation states of iron
    −2 [Fe (CO)4] 2−, [Fe (CO)2(NO)2]
    −1 [Fe2(CO)8] 2−
    0 Fe (CO)5, Fe2(CO)9, Fe3(CO)12
    +1 [Fe (H2O)5NO] 2+
    +2 FeCl2, FeSO4, FeO, Fe (OH)2, Ferrocene
    +3 FeCl3, Fe2O3, Fe (NO3)3, FeO (OH)
    +4 Li2FeO3, BaFeO3
    +5 FeO4 3−
    +6 K2FeO4, BaFeO4

    Iron is resistant in dry air, in dry chlorine as well as in concentrated sulfuric acid, concentrated nitric acid and basic agents (except hot sodium hydroxide solution) with a pH value greater than 9. This resistance is due to the presence of a cohesive protective oxide skin. In non-oxidizing acids such as hydrochloric acid and dilute sulfuric or nitric acid, iron dissolves rapidly with the evolution of hydrogen. [102] [79]

    It is also decomposed by water above 500 ° C and by hot alkalis in a reversible reaction: [79]

    Concentrated caustic soda attacks iron even in the absence of air, this goes into solution with hydroxoferrate (II) formation. In humid air and in water that contains oxygen or carbon dioxide, iron is easily converted to form iron oxide hydrate (Roast) oxidized. Since the resulting oxide layer is soft and porous, the rusting process can proceed unhindered. Sea water or SO containing electrolytes is particularly aggressive2-containing water in industrial areas. If iron is heated in dry air, a thin layer of iron (II, III) oxide (Fe3O4, Iron hammer blow), which is strongly colored (Tempering). Very finely divided, pyrophoresis Even at room temperature, iron reacts with oxygen from the air under the appearance of fire. Burning steel wool reacts vigorously in moist chlorine gas with the formation of brown iron (III) chloride vapors. If a mixture of iron and sulfur powder (in a weight ratio of 7: 4) is heated, mainly iron (II) sulfide is formed. [103] Even with other non-metals such as phosphorus, silicon, sulfur and carbon, iron forms phosphides, silicides, sulfides or carbides at elevated temperatures. [102] [79]

    Smell of iron

    Pure iron is odorless. The typical smell, classified as metallic, when you touch iron objects, is caused by a chemical reaction of substances in the sweat and the fat of the skin with the divalent iron ions that are formed in the process. [104]

    One of the most important scent carriers is 1-octen-3-one, which, even when diluted, has a mushroom-like metallic smell. [67] This accounts for about a third of the odor. The rest are other aldehydes and ketones. The preliminary stage of odorous substances are lipid peroxides. [105] These occur when skin oils are oxidized by certain enzymes or non-enzymatic processes (e.g. the UV component of light). These lipid peroxides are then broken down by the divalent iron ions, forming the fragrances. The divalent iron ions result from corrosion of the iron when it comes into contact with hand perspiration, which contains corrosive organic acids and chlorides. [105]

    When blood is rubbed on the skin, a similar odor arises, since blood also contains iron (II) ions and these form odorous substances through similar reactions. [105]

    Heavily rusted objects (including the formation of iron (III) compounds) do not emit a metallic odor when they are touched, as everyday experience shows. In agreement with this is the observation that the decomposition of lipid peroxides is not catalyzed by iron (III) ions. [105]

    Hazardous substance labeling

    While iron in massive form is not a hazardous substance, iron powder can be flammable, and in finely divided form even pyrophoric. Accordingly, such powders must be provided with an additional hazard label. [12]

    Iron has 27 isotopes and two core isomers, four of which are naturally occurring, stable isotopes. They have the relative frequencies: 54 Fe (5.8%), 56 Fe (91.7%), 57 Fe (2.2%) and 58 Fe (0.3%). The isotope 60 Fe has a half-life of 2.62 million years, [11] 55 Fe of 2.737 years and the isotope 59 Fe one of 44.495 days. [106] The remaining isotopes and the two core isomers have half-lives between less than 150 ns and 8.275 hours. [107] The existence of 60 Fe at the beginning of the formation of the planetary system was confirmed by the evidence of a correlation between the abundances of 60 Ni, the decay product of 60 Fe, and the abundances of the stable Fe isotopes in some phases of some meteorites (for example in the Meteorites Semarkona and Chervony Kut [108]) can be demonstrated. It is possible that the energy released during the radioactive decay of 60 Fe, in addition to the atomic decay energy of the radioactive 26 Al, also played a role in the melting and differentiation of the asteroids immediately after their formation about 4.6 billion years ago. Today the originally present 60 Fe has decayed into 60 Ni. The distribution of nickel and iron isotopes in meteorites makes it possible to measure the abundance of isotopes and elements during the formation of the solar system and to identify the conditions prevailing before and during the formation of the solar system. [109] [110]

    Of the stable iron isotopes, only 57 Fe has a nuclear spin other than zero. It is therefore suitable for Mössbauer spectroscopy. [111]

    In contrast to carbon-containing iron, chemically pure iron has only a subordinate technical importance and is used, for example, as a material for catalysts, among other things. the Haber-Bosch process or the Fischer-Tropsch synthesis. [79]

    Most of the iron produced is the main component of steel and cast iron. With 95 percent by weight of the metals used, iron is the most widely used worldwide. The reason for this lies in its wide availability, which makes it quite inexpensive, and in the fact that steel achieves excellent strength and toughness when it forms alloys with other metals such as chromium, molybdenum and nickel, which make it one for many areas of technology Make base material. [112] It is used in the manufacture of land vehicles, ships and in the entire construction sector (reinforced concrete construction, steel construction). Other areas of application are packaging (cans, containers, containers, buckets, strips), pipelines, pressure vessels, gas bottles and springs. [78] Various types of steel are widely used in industry in Germany, around 7,500 types are standardized. [113]

    Iron is used as a material in the following forms:

      contains four to five percent carbon and various proportions of sulfur, phosphorus and silicon. It is an intermediate in the manufacture of cast iron and steel. [79] contains over 2.06% carbon and other alloy elements, such as silicon and manganese, which improve castability. Cast iron is very hard and brittle. It usually cannot be plastically deformed (forged), but it can be poured very well because of its comparatively low melting point and the low viscosity of the melt. [114] contains a maximum of 2.06% carbon. In contrast to cast iron, it is forgeable. Alloying and a suitable combination of thermal treatment (see hardening) and plastic forming (cold rolling) can vary the mechanical properties of the steel within wide limits. [79]

    Iron (along with cobalt and nickel) is one of those three ferromagnetic metals which, thanks to their properties, allow the large-scale use of electromagnetism, among other things. in generators, transformers, chokes, relays and electric motors. [115] It becomes pure or, among other things. Alloyed with silicon, aluminum, cobalt or nickel (see Mu-Metal) and serves as a soft magnetic core material for guiding magnetic fields, for shielding magnetic fields or for increasing inductance. For this purpose, it is produced in bulk and in the form of sheet metal and powder (powder cores). [116] [117]

    Iron powder is also used in chemistry (for example as a catalyst in ammonia synthesis [118]) and is used in appropriate types of tape for magnetic data recording. Iron wire was used to record data in the wire-tone device [119] and is used, inter alia. used to manufacture wire ropes.

    In medicine, iron-containing preparations are used as anti-anemics, causally in the treatment of iron deficiency anemia and additively in the treatment of anemia caused by other causes. [120]

    Part of living beings

    Iron is an essential trace element for almost all living things, especially for blood formation in animals.

    In plant organisms it influences photosynthesis as well as the formation of chlorophyll and carbohydrates, [103] since in plants iron-containing enzymes are involved in photosynthesis, chlorophyll and carbohydrate formation. In plants, iron occurs almost exclusively in the form of free inorganic iron ions. The nitrogenase (nitrogen fixation) also contains iron (as well as the element molybdenum). There are plants that make iron ions bioavailable from calcareous soils through phyto-siderophores (iron-complexing compounds) in combination with the local release of hydrogen ions, during which Fe 3+ is reduced to Fe 2+ and then complexed. In plants, like in the liver, iron is bound to phytoferritins. In plants it is absolutely necessary for chlorophyll synthesis. If the iron content in plants falls below a critical minimum, the green parts of the plant become pale and yellow (chlorosis). [67]

    Iron compounds also play an important role in fungi (for example as ferrichrome, a siderophore with growth-promoting properties), bacteria (in Streptomyces the ferrioxamine B is formed) and sea worms (in them and in the lingula the non-heme iron protein hemerythrin occurs). [67]

    In the body of humans and animals it is oxidized as iron 2+ and iron 3+. As the central atom of the cofactor heme b in hemoglobin, myoglobin and cytochromes, it is responsible for oxygen transport and storage as well as electron transfer in many animals and humans. In these proteins, it is surrounded by a planar ring of porphyrin. [67]

    Iron is also a component of iron-sulfur complexes (so-called iron-sulfur clusters) in many enzymes, for example nitrogenases, hydrogenases or the complexes of the respiratory chain. The third important class of iron enzymes are the so-called non-heme iron enzymes, for example methane monooxygenase, ribonucleotide reductase and heme ythrin. These proteins perform tasks in various organisms: oxygen activation, oxygen transport, redox reactions and hydrolysis. [67] Trivalent iron is just as important as the central ion in the enzyme catalase, which breaks down the cell poison hydrogen peroxide, which is produced in the metabolism, in the peroxisomes of the cells. [121]

    The iron is stored intracellularly in the enzyme ferritin (20% iron content) and its breakdown product hemosiderin (37% iron content). Iron is transported through transferrin. [122]

    Humans contain 2.5 to 4 g of iron, of which 60% (2.0 to 2.5 g) is found in the hemoglobin of the erythrocytes, about 1 g in the liver and bone marrow (storage proteins ferritin and hemosiderin), about 10% to 15% % in myoglobin (approx. 400 mg iron), 250 mg in enzyme systems 0.1 to 0.2% iron in transport proteins (e.g. sulfur, iron proteins, cytochromes) (cytochrome: 0.1% of total iron). [67]

    External electron donor and acceptor

    Some bacteria use Fe (III) as an electron acceptor for the respiratory chain. You thus reduce it to Fe (II), which means that iron is mobilized, since most Fe (III) compounds are sparingly soluble in water, but most Fe (II) compounds are readily soluble in water. Some phototrophic bacteria use Fe (II) as an electron donor for the reduction of CO2. [123]

    Iron requirement and iron deficiency

    Iron in the Fe 2+ and Fe 3+ oxidation state is essential for all organisms. The daily requirement is 1 mg for men and 2 mg for women. Due to the inefficient absorption, the dietary intake must be around 5 to 9 mg for men and 14 to 18 mg for women. Iron deficiency is most likely to occur in pregnant women and athletes. An infant can absorb approx. 50% of the iron from breast milk, and only 20% from cow's milk. [67]

    Pre-menopausal women, in particular, are often iron deficient, the reason for this being menstruation. You should be consuming about 15 milligrams of iron per day, while the daily requirement of an adult male is only about 10 milligrams. In addition, women lose around 1000 milligrams of iron when giving birth to a child. By taking vitamin C at the same time, the absorption rate of iron is significantly increased. Iron is particularly rich in black pudding, liver, legumes and whole grain bread, and only slightly in (muscle) meat. However, consuming dairy products, coffee or black tea at the same time inhibits iron absorption. [124]

    Toxicity and iron overload

    People

    Iron is an important trace element for humans, but can also be harmful if overdosed. [125] [126] [127] This particularly affects people who suffer from hemochromatosis, a regulatory disorder of iron absorption in the intestine. The iron accumulates in the liver during the course of the disease, where it leads to siderosis and further organ damage. [67]

    Furthermore, iron is suspected of being infectious diseases, e.g. B. to promote tuberculosis, since the pathogens also need iron to multiply. [128] An oversupply of iron leads to an increased susceptibility to infectious diseases (tuberculosis, salmonellosis, AIDS, yersiniosis). [67] In addition, some neurodegenerative diseases such as Parkinson's or Alzheimer's disease cause iron deposits in certain areas of the brain. It is currently unclear whether this is a cause or a consequence of the disease. [129]

    Therefore, iron supplements, like other dietary supplements, are only recommended if there is a medically diagnosed iron deficiency.

    Plants

    Iron is also an essential trace element in plant organisms. It influences photosynthesis as well as the formation of chlorophyll and carbohydrates. [103] However, iron overload can manifest itself in the form of iron toxicity. In soils it is at normal pH values ​​as Fe (OH)3 before. If the oxygen content of the soil is low, iron (III) is reduced to iron (II) through reduction. This brings the iron into a soluble form that is available to plants. If this availability increases too much under anaerobic conditions, for example due to soil compaction, damage to plants can occur due to iron toxicity, a phenomenon that is particularly known in rice-growing areas. [130]

    There are a number of detection methods for iron. In addition to spectral analytical methods (iron provides a very rich spectrum), diverse chemical detection methods are also known. In the detection reaction for iron ions, a distinction is first made between the two cations Fe 2+ and Fe 3+. [131]

    Detection of iron with thioglycolic acid

    Fe 2+ and Fe 3+ ions can be detected with thioglycolic acid: [115]

    The presence of Fe 2+ or Fe 3+ ions produces an intense red color.

    Detection of iron with hexacyanoferrates

    The Fe 2+ ions can be detected with red blood liquor salt:

    Fe 3+ ions can be detected with yellow blood liquor salt:

    Both detection reactions produce deep blue Berlin blue, an important dye. There is no complex formation reaction, only a cation exchange.

    Both pigments are largely identical because there is a chemical equilibrium between them. Fe 3+ changes into Fe 2+ and vice versa: [132] [133] [134]

    The particularly intense blue color of the complex is created by metal-to-metal charge transfers between the iron ions. It is noteworthy that this well-known iron detection reagent itself contains iron, which is chemically well masked by the cyanide ions (inner orbital complex) and thus shows the limits of chemical analysis.

    Detection of iron with thiocyanates

    Alternatively, iron (III) salts with thiocyanates (rhodanides) can be detected. These react with iron (III) ions to form iron (III) thiocyanate: [135]

    The deep red iron (III) thiocyanate (Fe (SCN)3), which remains in solution. However, some accompanying factors interfere with this detection (e.g. Co 2+, Mo 3+, Hg 2+, excess mineral acids), so that a cation separation process may have to be carried out.

    In its chemical compounds, iron occurs mainly with the oxidation states +2 (e.g. iron (II) chloride), +3 (e.g. iron (III) fluoride), and also +6 (e.g. barium ferrate ( VI)), but there are also compounds with the oxidation states -2, -1 and 0 (e.g. iron pentacarbonyl) as well as +1, +4 and +5. In no compound does iron appear in the oxidation state corresponding to its subgroup number VIII. Even compounds with iron in the +7 oxidation state are unknown. [79]

    Oxides

    Iron forms divalent and trivalent oxides with oxygen:

    • Ferric oxide (Fe2O3) is a red to brown substance and is produced by the oxidation of iron in excess oxygen. In nature it occurs in the form of the minerals hematite and maghemite.
    • Iron (II, III) oxide (Fe3O4) occurs naturally through volcanic processes or when iron is burned directly, e.g. B. with the cutting torch as a hammer blow and is referred to as a mineral as magnetite.
    • Ferrous oxide (FeO) is only formed with the careful decomposition of iron (II) oxalate FeC2O4 in a vacuum. It is black and unstable up to 560 ° C. As a mineral wüstite, it usually arises from the transformation of magnetite at high temperatures.

    In addition, with FeO2 Another iron oxide is also known. [136]

    Since these oxides do not form a solid protective layer, an iron body exposed to the atmosphere oxidizes completely. The porous oxide layer slows down the oxidation process, but cannot prevent it, which is why burnishing serves as poor protection against corrosion. [137] If iron bodies are collected and recycled before they are finally rusted, rusted iron and rusted steel are coveted and valuable oxygen carriers in steel production in the electric smelting furnace. This oxygen in scrap iron acts as an oxidizing agent during "steel boiling" in order to oxidize undesired quality-reducing impurities (e.g. light metals).

    Iron (III) hydroxide oxide (FeO (OH)) belongs to the group of iron hydroxides or iron (III) oxide hydrates, which differ in their degree of hydration. When heated, iron (III) oxide hydroxide changes into iron (III) oxide. The α-form occurs naturally as needle iron ore or goethite. The y-shape occurs naturally as ruby ​​mica or lepidocrocite. In the α-form it has an orthorhombic crystal structure, space group Pbnm (Room group no. 62, position 3) Template: Room group / 62.3. [138]

    Iron oxides and iron hydroxides are used as food additives (E 172).

    Salts

    Iron forms divalent and trivalent salts:

    • Ferrous chloride (FeCl2 · 6 H.2O) is used for the precipitation of sulphides, digester gas desulphurisation, biogas desulphurisation, chromate reduction and phosphate elimination, this includes simultaneous precipitation. It has a crystal structure of the cadmium (II) chloride type with the space groupR. 3 m (Room group no.166) Template: Room group / 166.
    • Ferrous fluoride is a white solid in its pure state, which is sparingly soluble in water. It has a rutile type crystal structure, space groupP.42/mnm (Room group no.136) Template: Room group / 136.
    • Iron (II) bromide and Ferrous iodide are crystalline, hygroscopic solids that have a trigonal crystal structure of the cadmium (II) hydroxide type with the space groupP. 3 m1 (room group no.164) Template: room group / 164 have.
    • Ferrous sulfate (FeSO4 · 7 H2O) is also called green salt because of its color, as a mineral melanterite. Applications such as iron (II) chloride and dried iron (II) sulfate as a chromate reducer, especially in cement against chromate allergy.
    • Ferric chloride (FeCl3 · 6 H.2O) can oxidize copper and dissolve it, so aqueous iron (III) chloride solutions can be used to gently etch circuit boards.
    • Iron (III) nitrate is used for tanning. In the textile industry it is used as a stain for cotton fabrics and for dyeing silk black by separating iron (III) hydroxide. It has also been used as a corrosion inhibitor for a long time. More recently, it has been used, not always successfully, to reduce the hydrogen sulfide concentration in pressurized sewage pipes.
    • Ferric sulfate is used in large sewage treatment plants for deodorising and precipitating phosphate (e.g. in drinking water treatment and industrial water disposal) and in the iron and steel industry as a pickling agent (e.g. for aluminum and steel). [139] A hemostatic and astringent effect is known in medicine.
    • Ferric chloride sulfate (FeClSO4)

    All iron salts are used, among other things, as flocculants and for phosphate elimination, including pre-precipitation, simultaneous precipitation, post-precipitation and floc filtration as well as the precipitation of sulphides, digester gas desulphurisation and biogas desulphurisation.


    Constancy of mass chemistry

    Basic chemistry knowledge of 9th grade.Class substance level = macroscopic (visible) level consideration of a portion of substance with recognizable and measurable properties particle level = submicroscopic level consideration of the smallest particles of a substance: atoms, molecules, ions substance properties can be explained on this level. Substance A certain amount of sodium carbonate, which has been precipitated from a saturated solution with carbon dioxide, washed and dried to constant mass, is weighed as precisely as possible, dissolved in water and an indicator such as methyl orange is added. Now it is titrated up to the point of transition. From the consumption of standard solution and the amount of substance used a The constancy of mass can be visualized with the help of a simple model analysis (Fig. 3). It becomes clear that the number of particles before and after the reaction has not changed, but that only a regrouping of the particles has taken place. The expansion of the balloon in the meantime is based solely on thermal expansion of the gas. From this closing condition it follows that the knowledge or determination of the mass concentrations of Z - 1 components is sufficient (in the case of a two-substance mixture, the mass concentration of one component), since the mass concentration of the remaining component can be calculated simply by forming the difference to the density ρ of the mixed phase (if this is known ) can be calculated

    This answer will seem stupid to you, but it is the only really serious answer. In practice, however, nobody has the nerve to constantly re-weigh a product, just to see whether it has become a little easier after all The law of the conservation of mass explained by means of an experiment. A video by the video chemistry group of the grammar school Antonianum Gesek

    Atomic mass unit - Wikipedi

    Chemistry class work with solutions, basic knowledge and exercises for grade 9 The finding apparently confirms the misconception that material is destroyed by the chemical reaction of burning. SV2 SV3: the constancy of mass is verified by precise weighing (and statistical evaluation of the group results, possibly eliminating errors). AS4: Securing: Brief descriptions of the experiments, observation and interpretation are noted in the exercise book. Formulation of a. Do atoms also have weight problems? Which are the heavy and which are the light atoms? You don't have an answer to that? Then watch the video and vo ..

    Law of Conservation of Mass - a simple explanation

    • Constancy of mass limit. 0.5 mg. Analytical chemistry. Factor calculation of the measurement solution? F (ML) = z (U) * m (U) * 100 / c (ML) * V (ML) * M (U) Analytical chemistry. Direct determination with NaOH. For the determination of: titration in / with: Vineloge carboxylic acids, hydrochlorides. Multiphase systems. Analytical chemistry. HCl Urtiter reaction. Na2CO3 + 2 HCl ---- & gt 2NaCl + H2CO3. Analytical chemistry. Argentoalkalimetry.
    • Definition. A complex compound consists of a central cation to which anions or uncharged molecules are bound as ligands. The ligands are usually bound to the central ion via lone pairs of electrons on the ligands. A distinction is made between addition complexes with many free, unpaired electrons (e.g. Aquo complexes) and.
    • Lego bricks, constancy of mass and the law of constant proportions. UC 14 (2003) No. 76/77, p. Full digital access to the content of the magazine “Lehr Chemie”. Comprehensive archive with over 250 didactic and technical articles, e.g. B. teaching units, worksheets, images, films, tasks, background information, and much more. m. over 100 new ones annually.
    • Gravimetry (chemistry) Gravimetry is a quantitative analysis method in which the measurement of substance quantities is based on the determination of the mass (weight). A distinction is made between precipitation analysis, electrogravimetry and thermogravimetry
    • Constancy of mass limit. 0.5 mg. Show Answer. Exemplary flashcards for Analytical Chemistry at the Technische Hochschule Köln on StudySmarter: Factor calculation of the measurement solution? F (ML) = z (U) * m (U) * 100 / c (ML) * V (ML) * M (U) Show Answer. Exemplary flashcards for Analytical Chemistry at the Technische Hochschule Köln on StudySmarter: Direct determination with NaOH. For the determination of: titration in.

    What is meant by constant weight (chemistry)? (University

    time until constant mass is reached (change in mass not more than 0.1%). One . Food chemistry internship University of Hamburg 9/103 Increase in mass is not taken into account the calculation is based on the lowest obtained weight in each case. Extraction, drying and weighing must immediately follow one another. The result is below. Gravimetry (chemistry) Gravimetry is a quantitative analysis method in which the measurement of the amount of substance is based on the determination of the mass (weight). A distinction is made between precipitation analysis, electrogravimetry and thermogravimetry. Gravimetry is a quantitative analysis method in which the measurement of substance quantities is based on the determination of the mass (weight). Precipitation analysis, electrogravimetry and thermogravimetry are again distinguished. Chemistry as a doctrine of substances, differentiation between object and substance • The SOS of chemistry - safety, order, cleanliness. Dr. A. Ledermann, University of Würzburg Institute for Organic Chemistry 1 1 Recrystallization of contaminated adipic acid with the help of activated carbon Note: The following is the original specification of the experiment instructions for recrystallization of contaminated adipic acid from the final examination part 1 for chemical laboratory technicians. The aim of the recrystallization is to take as much as possible.

    Gravimetry (chemistry) - chemistry school

    Washed water at 5 ° C. The benzoic acid is dried to constant mass at 90 ° C. in a drying cabinet. Reaction equation. Download. Benzoic acid from benzaldehyde. Details. Syntheses organic chemistry content. Experiments Overview of the show experiments. Analytics experiments from analytics DNA experiments with DNA color Experiments that show a color or a color change. & gt Checking the constancy of mass in closed systems after the formation of new phases Scientists in the disciplines of physics and chemistry already learn during their studies that mass is a conserved quantity in a thermodynamically closed system Apr 2013 12:08 Title: weight constancy: My question: Hello! can someone explain to me what exactly is meant by constant weight? My ideas: `My assumption is that it is the weight where no more water (moisture) escapes. Daniel35 Registration date: 10.09.2012 Articles: 1127. Aspects / sub-contexts: chemical reaction Competence lists, process-related, concept-related Content field Air and water Standard content Constancy of mass in the reaction of wood with oxygen (balloon cap) with simple carbon cycle Experiment: Heating matches in a closed test tube Oxygen CR I 3 CR I.7a CR II 10 Law of the conservation of mass.

    Practical course in inorganic chemistry / titer determination. From Wikibooks & lt Internship Inorganic Chemistry. Jump to navigation Jump to search. The titer or normal factor f is a factor that indicates the deviation of the actual concentration of a standard solution from the nominal concentration of the solution. : = .. This results in the titration with the set solution = ⋅ ⋅. The titer. Chemistry Angew. Material science Inorganic practical course, 1st semester, test specifications. 2 Gravimetry determination of nickel You receive a solution that contains 0.1 - 0.2g nickel. Working instructions: 20 ml of the sample solution are pipetted into a 400 ml beaker, diluted to approx. 200 ml and heated to 80 ° C. (Cover the beaker with a watch glass) Then slowly let 25. Lego bricks, constancy of mass and the law of constant proportions 76/77, 225 Graf E .: Exercise chemical detection reactions 74, 89 Graf E., Sommer K .: Practice and repeat in chemistry lessons 74, 56 Grob, P .: About the sense and nonsense of chemical symbolism in secondary level I 75, 142 Gröger M .: see Scheffers-Sap M. 74, 92 Große-Ophoff M., Wagner G .: Additives for plastics . Folder management for CHEMISTRY atomic construction and bonding theory 2/4. Select the folder to which you want to add or remove CHEMIE Atomic Structure and Bonding Theory 2/4 Chemical methods 1) Carbide method dry for 2-3 hours until the mass is constant (- & gt mass must not decrease) • possible increase in mass (due to Do not take into account fat oxidation) • Let the aluminum dish cool down in the desiccator before reweighing. Possible errors: • Temperature too low or time too short selected (- & gt water not completely evaporated.

    Analytical chemistry Summary analysis parameters: a) Sensitivity b) Accuracy c) Reproducibility d) Time required f) Automation g) Costs KS value: 50% dissociated and 50% not dissociated pH value of a Na2S solution, C0 = 10-2 mol / la) Dissociation: Na2S ↔ 2 Na + + S2- protolysis equations: S2- + H2O ↔ HS- + OH- S2- + 2 H2O ↔ H2S + 2 OH- H2O↔ H + + OH- b. Internship Inorganic Chemistry I (CHE-100-051-L-1) Academic year. 2017/2018. Helpful? 2 0. Share. Comments. Please log in or register to write comments. Similar documents. Test protocol AT 7 Tetrabutylammonium perchlorate Test protocol silver recovery Exercise B4 Exercise Repeat sheet Exam topics Cobalt acetylacetone dinitrogen tetroxide. Text. The product is dried to constant mass at 60 ° C in a circulating air cabinet. Org. Chemical laboratory internship Page 4 of 4 5.0 Determination of the yield The calculation is based on the theoretical yield of methyl orange based on the use of 1.5 g or 0.012 mol of N, N-dimethylaniline in a.

    A certain amount of sodium carbonate, which was precipitated from a saturated solution with carbon dioxide, washed and dried to constant mass, weighed as precisely as possible, dissolved in water and mixed with an indicator such as methyl orange Chemistry: barium carbonate + hydrochloric acid - BaCO3 + 2HCl ↔ BaCl2 + CO2 + H2O - & gt barium chloride + carbon dioxide + water. General Chemistry for Chemistry (1411051) Academic year. 2019/2020. Helpful? 0 0. Share. Comments. Please log in or register to write comments. Students also saw. Exercises - tasks (questions) Examenes 30 June winter 2009, preguntes exam 27 February winter semester 2017/2018, questions. Other similar documents. Exam March 10, 2010, questions. The mass constancy applies: c0 = [A] + [AB] = [B] + [AB] The electrical neutrality (charge constancy) applies: [A] = [B] degree of dissociation a = = = = 1 - Þ [AB] = c0 * (1-a) [A] = [B] = ac0. MWG: KC = = c0 Ostwald's law of dilution. The degree of dissociation increases with decreasing total concentration, i.e. with increasing dilution. a = approximation: for large [AB] with small dissocia

    Constancy of mass and the law of conservation of energy? (School, chemistry

    1. Homogenize chemistry. We have been supplying our products to industrial and large customers for over 40 years. ESSKA.de by professionals for professionals! Over 120,000 professional items for your use Over 80% new products at a fixed price This is the new eBay. Findchemistry! Huge selection of brand quality. Follow your passion on eBay The aim of homogenization is to find the mean diameter of the.
    2. Preparatory exercises Inorganic chemistry Chemistry of phosphorus Exercise 4-6, 2004 Determine the compounds A to K. Notes: The stoichiometric ratios are not given. Q: One equivalent of chloroalkane is produced as a by-product. J: J is a salt. D E I EtOH PhMgBr (excess) P P P P A B O
    3. Chemistry and biochemistry From atom to respiration - for biologists, physicians and pharmacists With 118 figures and 64 tables Second, revised and expanded edition A & # 92 ^ J Springer. Content Matter, Energy, Life 1 1.1 Characteristics of the living 3 1.2 Dividing and growing 4 1.3 Chemistry and physics as a basis 5 1.4 Forms, structures and functions in nature 7 1.5 Energetics - without.
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    5. Laboratory Chemistry of Nutrition V4-Stand 02.11.2016 Water content Page 2 of 7 Sorption isotherms: Experimental The process is repeated until the mass is constant. This is achieved when the mass decrease does not exceed 0.5 mg between 2 successive drying cycles. If the mass increases again, the lowest mass is used to calculate the water content. For the.
    6. Brought mass constancy. After cooling to room temperature, the weight is determined. In addition to the determination of nickel, it can be said that the precipitate is noticeably soluble in hot water and should therefore only be washed with as little hot water as possible. Weighing form Ni (C4H7O2N2) 2 - desired form Ni F = 0.2031

    Gravimetry_ (chemistry

    Folder management for chemistry year 1. Select the folders to which you want to add or remove chemistry year 1 Basic knowledge of physics, chemistry and biochemistry From the atom to breathing - for biologists, physicians and pharmacists 3rd, extended and updated edition fyj. Springer spectrum. Matter, Energy, Life 1 1.1 Characteristics of the living 3 1.2 Divide, grow and multiply. . 4 1.3 Chemistry and physics as a basis 6 1.4 Forms, structures and functions in nature 8 1.5 Energetics - without energy consumption. Titriplex III solution In analytical chemistry (quantitative analysis), EDTA is used as a complexon / Titriplex II standard solution to quantitatively determine metal ions such as Cu, Pb, Hg, Ca or Mg in chelatometry. The disodium salt (complexon / Titriplex III), which is more soluble in water, can also be used for 1000 ml, c (Na₂-EDTA 2 H₂O) = 0.1 mol / l Titrisol® Titriplex® I

    The resulting precipitate is filtered hot, washed with warm water and dried over calcium chloride in a desiccator until the mass is constant. The dried powder is then placed in a round-bottomed flask together with 60 mL toluene and brought to the boil under reflux. The quinizarin crystallizes out on cooling. If a higher purity is desired, the quinizarin is dissolved in.School-internal core curriculum for chemistry in year 7 This in-house curriculum only lists the abbreviations of the competencies. The formulated areas of competence can be found in the list (see attachment). Fields of content Subject-specific contexts Concept-related skills Process-related skills Methods / possible courses 0. x Introduction to chemistry Chemistry. Basic knowledge of physics, chemistry and biochemistry: from atom to breathing - for biologists, physicians, pharmacists and agricultural scientists Subject: Berlin, [Heidelberg], 2019 Keywords: Signature of the original (print): T 19 B 1651. Digitized by TIB, Hanover , 2020. Created Date: 7/27/2020 2:47:31 P It is one of the most important measuring instruments for chemists. There is hardly a field of work in chemistry in which weighing can be dispensed with. The main applications extend to the weighing of substances for the purpose of analysis or preparative further processing, to weighing (back weighing) for evaluation or to the direct tracking of changes in mass during the process.

    Titer_ (chemistry

    1. de.sci.chemie. Discussion: meaningful chemistry lesson (too old for an answer) Bernd Miller 2004-04-30 12:43:42 UTC. Permalink. As a chemistry teacher, I have a question that has moved me for a long time. It's about chemistry classes in middle school (e.g. secondary school). The majority of my school leavers are learning a solid profession - such as a nurse, banker, baker.
    2. The nutsch residue is then transferred to a porcelain dish and dried at 90-95 ° C in a drying cabinet to constant mass. Acetylsalicylic Acid Chemistry. Properties, structure and production Acetylsalicylic acid (2-acetoxybenzoic acid) is a slightly acidic, crystalline substance. Experiment: Production of acetylsalicylic acid from salicylic acid. Devices.
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    5. The prerequisite is that there is no chemical change in the material at this temperature. If this is the case, drying must be carried out at a lower temperature. For gypsum, for example, the drying temperature is 40 ° C, because at 45 ° C it gives off part of its crystal water and changes into the ß-hemihydrate. The humidity in the drying room must be kept sufficiently low. Will.
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    Mass concentration - Wikipedi

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    3. We had a class test in chemistry this morning. Among other things, the following task was found: Assume that potassium and oxygen are formed from 940g of potassium oxide. Formulate the reaction equation and state how many grams of potassium, how many grams of oxygen and how many liters of oxygen are produced
    4. Gravimetry is a quantitative analysis method in which the measurement of the amount of substance is based on the determination of the mass, whereby a distinction is made between precipitation analysis, electrogravimetry and thermogravimetry. Precipitation analysis process Here the ions or molecules are brought into a form of precipitation. The precipitated compound is filtered off, washed and dried

    Department of Biology, Chemistry, Pharmacy

    1. in - the thoroughness, conscientiousness, diligence To the full article → Firmness. Noun, fe
    2. Chemistry and Director of the II. Chem. Institute of the Univ. Berlin. L. wrote around 70 scientific Treatises on opt. Properties organ. Compounds, vapor pressures, melting points and the constancy of mass in reactions. Member of the Preuss. Akad. Der Wissenschaft, the Akad. Der Wissenschaften St. Petersburg, honorary member of the Bunsen Society for Physics. Chemistry, 1905 golden.
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    4. 2.1.3 Constancy of mass. 27 2.1.4 Volume and density 13.1 Organic chemistry and biochemistry are not identical. 290 13.2 Organic substances are carbon compounds. 291 13.3 Alkanes form the basis of the.

    The Law of Conservation of Mass - Videochemie AG

    1. At a laboratory graduation ceremony in the courtyard of the Institute for Pharmaceutical Chemistry in Jena, the students let parts of their lab coats fly into the sky. Photo: Theresa Weise. So it went on after the semester break with the world of salary determinations. The laboratory work became even more demanding, because the qualitative analysis requires a high degree of accuracy. A good pharmacist.
    2. A constant mass is achieved at 400 ° C. The green fibers were heated to a temperature of 1310 ° C and then examined radiographically for their phase composition. The Diffrak-togram generated in this way shows reflections that could all be assigned to mullite. The developments are to be continued. Larger quantities of pulp are required for further scale-up.
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    Chemistry grade 9 - class tests

    He is certainly one of the fathers of chemistry, when the astounding observation of the constancy of mass is to include the air weighed in the consideration, the carbon-oxygen reaction and the formation of carbon dioxide of the same mass. If the Dalton atomic model is available, the reaction can be initiated by rearranging the C atoms and O 2 molecules. Colititer of a water sample with lactose peptone broth with Durham fermentation tubes (1000 to 9999 CFU / ml) The titer or normal factor f in analytical chemistry is a factor that determines the deviation of the actual concentration of a measurement solution 25) ° C heated to constant mass. The loss on ignition is calculated from the difference between the masses before and after the annealing process. The determination is carried out on a previously dried sample or directly on a non-dried sample with inclusion of drying or with reference to the dry mass. Of the. LM Chemistry: Learn E - LM Chemistry online for free. stay logged in | Forgot password (flour at 900 ° C) after reaching constant mass What is food dry matter made of? Organic substances: CO2, H2O, NOx Minerals: ash What forms of binding of minerals are there? Free ions e.g. Ca2 +, Na +, Cl-, F- - & gt dissolved in water or precipitated as salt.

    Samples dried to constant mass at 105 ° C. The detection and quantification limits of the method were between 0.03 ng / g dw for UV 327 and 0.90 ng / g dw for OC and 0.10 ng / g dw for UV 327 and 2.70 ng / g dw for OC. The names of the detected UV stabilizers and UV filters are compiled in Table 1. 03/2006, BR Conversion of Humidity Units Page 2 GREISINGER electronic GmbH Hans-Sachs-Strasse 26 Tel .: 09402 / 9383-0 http://www.greisinger.de D-93128 Regenstauf. Let the sample glow for 2 to 4 hours until the mass is constant. Chemical laboratory tests - Part 3: Determination of loss on ignition and residue on ignition DIN 19684-3: 1977-02 - Soil investigation method in agricultural hydraulic engineering Chemical laboratory tests, determination of loss on ignition and residue on ignition Literature. Blume, H.-P., Stahr, K., Leinweber, P. LM- Chemie: How can the mineral content of a food be determined? - Food is dried and milled, a defined sample amount is weighed into a porcelain crucible and the material in the.

    Video: Lesson plan SI / SII: Conservation of mass - Didactics of chemistry

    Dry to constant mass. Interpretation Translation dry to constant mass v: dry to constant mass v: dry to constant mass. German-English specialist dictionary architecture and construction. 2013. dry to constant weight bitter end. , Chemkon - Chemie Konkret, Forum Fuer Studium Und Didaktik on DeepDyve, the largest online rental service for scholarly research with thousands of academic publications available at your fingertips From the Institute for Organic Chemistry and Macromolecular Chemistry at Heinrich Heine University Düsseldorf Printed with the . It can happen that two phases form, but this has no effect on the yield. The product is suctioned off at room temperature and diluted with 100 mL dist. Washed water at 5 ° C. The benzoic acid is at 90 ° C in the drying cabinet until the mass is constant. #LID 1033 1 1537 Deposition rhythm overburden salts separation separation phase stripping section acetaldehyde acetaminobenzoic acid acetaminotoluene acetic anhydride acetanilide acetacetic water absorption largely constant. In contrast to the two other zero ducks, this one is only approximately half as large. In addition, with this cement there is hardly any influence of the Wasserze ment value on the total water absorption and thus on the pore structure

    The chemical reaction concept as the central basic concept of chemistry is the focus of the specialist knowledge, C The constancy of mass despite the disappearance and formation of substances in the match ampoule 3. B The volume contraction when mixing alcohol and water (and the volume expansion when mixing acetone and heptane) - see Table 1 (below) The various. The ideal textbook for physics and chemistry in biology, medicine, pharmacy, nutritional and environmental sciences. Year: 2013. Edition: 3. Publisher: Springer Spektrum. Language: german. Pages: 510/508. ISBN 13: 978-3-642-36635-2. Series: Bachelor. File: PDF, 7.29 MB. Preview. Send to Kindle or email address. Please log in first. Need help? Please read. Chemistry_18_2007 class No. 1001101. 29 Removal of dye with chalk. You have seen how mixed colors separate from rising water on a piece of chalk, because they are taken along differently. The various dyes dissolve better or worse in water and adhere better or worse to the chalk. How it leads to an on. Constant mass weighed [16]. 2.3.4 Quantification of the protein content The protein content was determined according to Kjeldahl [17]. The total nitrogen content was determined via the oxidative decomposition of the sample and calculated back to the protein content in the sample. Implementation e1 & # 92 & # 928 'From textbook experiment to the law of constant proportions

    1 & # 92g. C & # 92 & # 92_ & ltJet & # 92-a.g · (W self-planned model test. Dagmar Steiner w

    Andrea Gerdes New Media - Other Methods 76 Developing Experiments 33. Volker Schlieker The preservation of the mass. Working in a team 80 Lutz Neider Experience in a basic chemistry course Getting started - but how.

    . In the case of charcoal and wood briquettes, the sample is incinerated at a temperature of 710 ± 15 ° C. The ash content is calculated from the difference in the masses before and after the annealing process. The determination is made on a previously dried sample. Freezing mixture use. In contrast to refrigerants, most refrigeration mixtures can be stored separately without a pressure vessel. Therefore, refrigeration mixtures are often used when low temperatures are to be generated and briefly maintained without a refrigeration machine (e.g. in the laboratory) Most of the refrigeration mixtures in. Tasks of the selection process 6 Foreword The Chemistry Olympiad is an annual school competition aimed at prospective high school graduates What type of chemical bond does the following compounds have? Li 2 O, Cl 2, SrCl 2 The Bohr atomic model in theory and by means of examples Draw the Bohr atomic model of boron! 137 56 Ba Basic definitions and terms of the general and anorg. Chemistry: pure substances, elements, compounds, homogeneous and heterogeneous mixtures, atomic number, mass number, electronegativity.

    Basic knowledge of physics, chemistry and biochemistry: from atoms to breathing - for biologists, physicians, pharmacists and agricultural scientists Horst Bannwarth, Bruno P. Kremer, Andreas Schulz This book provides a compact overview of the entire basic knowledge of physics, chemistry and biochemistry in easily understandable texts and figures, with restriction to what is really necessary The chemical potential of the swelling agent in a swollen network To determine the chemical potential of a gel mixing phase, the expressions derived in Chapters 5.1 and 5.2 for the quantities DG m and DG el + DG vern are used according to (5.37) to express the change in the free enthalpy of a gel caused by swelling, DG q. Here in. Basic knowledge of physics, chemistry and biochemistry: from atoms to breathing - for biologists, physicians and pharmacists | Horst Bannwarth, Bruno P. Kremer, Andreas Schulz | download | B-OK. Download books for free. Find book


    The saturation vapor pressure in the phase diagram

    In the phase diagram, the saturation vapor pressure is the value of the pressure along the phase boundary line, marked here as black, between the gas phase and the corresponding solid or liquid phase. This phase boundary line is therefore also called Vapor pressure curve or Saturation vapor pressure curve designated. For the phase equilibrium of gas-solid bodies, the saturation vapor pressure is also called sublimation pressure and for the phase equilibrium of gas-liquid it is also called the boiling pressure. It should be noted here that at temperatures above the critical point there is no longer a liquid phase and therefore no saturation vapor pressure either. Furthermore, the phase boundary line between solid and liquid, the so-called melting curve, does not play a role for the saturation vapor pressure.


    Bell-Evans-Polanyi principle

    That Bell-Evans-Polanyi principle is a model that establishes an energetic relationship between the activation enthalpy and the reaction enthalpy of a chemical reaction. It says that within a series of similar reactions, there is a linear relationship between the above reaction constants. & # 911 & # 93 The activation enthalpy is lower the lower the reaction enthalpy. The basics were found in publications by in the 1930s R. P. Bell & # 912 & # 93 as well M. G. Evans and M. Polanyi & # 913 & # 93 described.

    The Bell-Evans-Polanyi principle allows both thermodynamic and kinetic statements to be formulated about a series of chemical reactions:

    1. Exothermic reactions have energetically more favorable (earlier, eduktmore similar) transition state.
    2. An energetically more favorable product causes a lower reaction barrier and thus a faster reaction (see also Arrhenius equation).

    The general derivation from the Bell-Evans-Polanyi principle is the Hammond postulate.

    A good example of the Bell-Evans-Polanyi principle is the pyrolysis of azo compounds. Here, molecular nitrogen is released from the azo compound used, with the radicals of the corresponding organic radicals being formed. The enthalpy of reaction ΔHR. depends on the energy content of the starting materials and the stabilization of the radicals that are formed. The activation enthalpies ΔHA. behave relatively like the enthalpies of reaction (see figure).


    Saturation vapor pressure

    Of the Saturation vapor pressure (even Equilibrium vapor pressure) of a substance is the pressure at which the gaseous state of aggregation is in equilibrium with the liquid or solid state of aggregation. The saturation vapor pressure depends on the temperature.

    the Saturation vapor pressure curve (Saturation vapor pressure line, vapor pressure curve, vapor pressure line) describes the saturation vapor pressure as a function of the temperature. It corresponds to the phase boundary line of the gaseous phase in the phase diagram.

    Attention: In chemistry, the saturation vapor pressure is usually abbreviated as "vapor pressure". There is a great risk here of confusing the term saturation vapor pressure with that of partial pressure. Therefore the term “vapor pressure” is not used here.


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