Stoichiometric coefficient. Determination of stoichiometric coefficients in the equations of redox reactions. Calculation scheme according to the equations of chemical reactions
When drawing up an equation for a redox reaction (ORR), it is necessary to determine the reducing agent, oxidizing agent, and the number of given and received electrons. OVR stoichiometric coefficients are selected using either the electron balance method or the electron-ion balance method (the latter is also called the half-reaction method). Let's look at a few examples. As an example of compiling OVR equations and selecting stoichiometric coefficients, we analyze the process of oxidation of iron (II) disulfide (pyrite) with concentrated nitric acid: First of all, we determine the possible reaction products. Nitric acid is a strong oxidizing agent, so the sulfide ion can be oxidized either to the maximum oxidation state S (H2S04) or to S (SO2), and Fe to Fe, while HN03 can be reduced to N0 or N02 (the set of specific products is determined concentrations of reagents, temperature, etc.). Let's choose the following possible option: H20 will be on the left or right side of the equation, we don't know yet. There are two main methods for selecting coefficients. Let us first apply the method of electron-ion balance. The essence of this method is in two very simple and very important statements. First, this method considers the transition of electrons from one particle to another with the obligatory consideration of the nature of the medium (acidic, alkaline, or neutral). Secondly, when compiling the equation of the electron-ion balance, only those particles are recorded that actually exist during the course of a given OVR - only really existing cations or annones are recorded in the form of ions; Substances that are poorly disociated, insoluble or liberated in the form of a gas are written in molecular form. When compiling the equation for the processes of oxidation and reduction, to equalize the number of hydrogen and oxygen atoms, one introduces (depending on the medium) either water molecules and hydrogen ions (if the medium is acidic), or water molecules and hydroxide ions (if the medium is alkaline). Consider for our case the oxidation half-reaction. Molecules of FeS2 (a poorly soluble substance) turn into Fe3+ ions (iron nitrate (II) completely dissociates into ions) and sulfate ions S042 "(dissociation of H2SO4): Now consider the half-reaction of reduction of the nitrate ion: To equalize oxygen, add 2 to the right side water molecules, and to the left - 4 H + ions: To equalize the charge to the left side (charge +3), add 3 electrons: Finally, we have: Reducing both parts by 16H + and 8H20, we get the final, reduced ionic equation of the redox reaction: Adding the corresponding number of NOJ nH+ ions to both sides of the equation, we find the molecular reaction equation: Please note that to determine the number of given and received electrons, we never had to determine the oxidation state of the elements. In addition, we took into account the influence of the environment and “automatically” determined that H20 is on the right side of the equation. There is no doubt that this method has a great chemical meaning. Empirical balance method. The essence of the method of finding the stoichiometric coefficients in the equations of the OVR is the obligatory determination of the oxidation states of the atoms of the elements involved in the OVR. Using this approach, we again equalize the reaction (11.1) (above we applied the method of half-reactions to this reaction). The reduction process is described simply: It is more difficult to draw up an oxidation scheme, since two elements are oxidized at once - Fe and S. You can assign iron an oxidation state of +2, sulfur - 1 and take into account that there are two S atoms per Fe atom: You can, however, do without determination of oxidation states and write down a scheme resembling scheme (11.2): The right side has a charge of +15, the left side has a charge of 0, so FeS2 must give up 15 electrons. We write down the overall balance: We still need to “figure out” the resulting balance equation - it shows that 5 HN03 molecules are used to oxidize FeS2 and another 3 HNO molecules are needed to form Fe(N03)j: To equalize hydrogen and oxygen, to the right part you need to add 2 molecules of H20: The electron-ion balance method is more versatile than the electron balance method and has an undeniable advantage in the selection of coefficients in many OTS, in particular, with the participation of organic compounds, in which even the procedure for determining oxidation states is very complicated . - Consider, for example, the process of ethylene oxidation, which occurs when it is passed through an aqueous solution of potassium permanganate. As a result, ethylene is oxidized to ethylene glycol HO - CH2 - CH2 - OH, and permanganate is reduced to manganese oxide (TV), in addition, as will be obvious from the final balance equation, potassium hydroxide is also formed on the right: After making the necessary reductions of such terms, we write the equation in the final molecular form * Influence of the medium on the nature of the OVR flow. The examples (11.1) - (11.4) clearly illustrate the "technique" of using the electron-ion balance method in the case of OVR flow in an acidic or alkaline medium. The nature of the environment! influences the course of one or another OVR; in order to “feel” this influence, let us consider the behavior of one and the same oxidizing agent (KMnO4) in different environments. , recovering up to Mn+4(Mn0j), and the minimum - in the strength of the last one, in which the risen Shaiyaaapsya up to (mvnganat-nOn Mn042"). This is explained as follows. The acids of the dissociation line form hydroxide ions ffjO +, which strongly polarize 4 "MoOH ions Weaken the bonds of manganese with oxygen (thereby enhancing the action of the reducing agent) .. In a neutral medium, the polarizing effect of water molecules is significantly c-aafep. >"MnO ions; much less polarized. In a strongly alkaline medium, hydroxide ions “even strengthen the Mn-O bond, as a result of which the effectiveness of the reducing agent decreases and MnO^ accepts only one electron. An example of the behavior of potassium permanganate in a neutral medium is represented by the reaction (11.4). Let us also give one example of reactions involving KMnOA in acidic and alkaline media
Which studies the quantitative relationships between the substances that entered into the reaction and formed during it (from other Greek "stechion" - "elemental composition", "meitren" - "I measure").
Stoichiometry is the most important for material and energy calculations, without which it is impossible to organize any chemical production. Chemical stoichiometry allows you to calculate the amount of raw materials needed for a particular production, taking into account the desired performance and possible losses. No enterprise can be opened without preliminary calculations.
A bit of history
The very word "stoichiometry" is an invention of the German chemist Jeremy Benjamin Richter, proposed by him in his book, in which the idea of the possibility of calculations using chemical equations was first described. Later, Richter's ideas received theoretical justification with the discovery of the laws of Avogadro (1811), Gay-Lussac (1802), the law of constancy of composition (J.L. Proust, 1808), multiple ratios (J. Dalton, 1803), and the development of atomic and molecular theory. Now these laws, as well as the law of equivalents, formulated by Richter himself, are called the laws of stoichiometry.
The concept of "stoichiometry" is used in relation to both substances and chemical reactions.
Stoichiometric Equations
Stoichiometric reactions - reactions in which the starting substances interact in certain ratios, and the amount of products corresponds to theoretical calculations.
Stoichiometric equations are equations that describe stoichiometric reactions.
Stoichiometric equations) show the quantitative relationships between all participants in the reaction, expressed in moles.
Most inorganic reactions are stoichiometric. For example, three successive reactions to produce sulfuric acid from sulfur are stoichiometric.
S + O 2 → SO 2
SO 2 + ½O 2 → SO 3
SO 3 + H 2 O → H 2 SO 4
Calculations using these reaction equations can determine how much each substance needs to be taken in order to obtain a certain amount of sulfuric acid.
Most organic reactions are non-stoichiometric. For example, the reaction equation for cracking ethane looks like this:
C 2 H 6 → C 2 H 4 + H 2 .
However, in reality, during the reaction, different amounts of by-products will always be obtained - acetylene, methane and others, which cannot be calculated theoretically. Some inorganic reactions also defy calculations. For example, ammonium nitrate:
NH 4 NO 3 → N 2 O + 2H 2 O.
It goes in several directions, so it is impossible to determine how much starting material needs to be taken in order to obtain a certain amount of nitric oxide (I).
Stoichiometry is the theoretical basis of chemical production
All reactions that are used in or in production must be stoichiometric, that is, subject to accurate calculations. Will the plant or factory be profitable? Stoichiometry allows you to find out.
On the basis of stoichiometric equations, a theoretical balance is made. It is necessary to determine how much of the starting materials will be required to obtain the desired amount of the product of interest. Further, operational experiments are carried out, which will show the real consumption of the starting materials and the yield of products. The difference between theoretical calculations and practical data allows you to optimize production and evaluate the future economic efficiency of the enterprise. Stoichiometric calculations also make it possible to compile the heat balance of the process in order to select equipment, determine the masses of by-products formed that will need to be removed, and so on.
Stoichiometric substances
According to the law of composition constancy proposed by J.L. Proust, any chemical has a constant composition, regardless of the method of preparation. This means that, for example, in a molecule of sulfuric acid H 2 SO 4, regardless of the method by which it was obtained, there will always be one sulfur atom and four oxygen atoms per two hydrogen atoms. All substances that have a molecular structure are stoichiometric.
However, substances are widespread in nature, the composition of which may differ depending on the method of preparation or source of origin. The vast majority of them are crystalline substances. One could even say that for solids, stoichiometry is the exception rather than the rule.
For example, consider the composition of well-studied titanium carbide and oxide. In titanium oxide TiO x X=0.7-1.3, that is, from 0.7 to 1.3 oxygen atoms per titanium atom, in carbide TiC x X=0.6-1.0.
Nonstoichiometric solids is explained by an interstitial defect at the nodes of the crystal lattice or, conversely, by the appearance of vacancies at the nodes. Such substances include oxides, silicides, borides, carbides, phosphides, nitrides and others. inorganic substances, as well as high-molecular organic.
And although evidence for the existence of compounds with a variable composition was presented only at the beginning of the 20th century by I.S. Kurnakov, such substances are often called berthollides by the name of the scientist K.L. Berthollet, who suggested that the composition of any substance changes.
All quantitative ratios in the calculation of chemical processes are based on the stoichiometry of reactions. It is more convenient to express the amount of a substance in such calculations in moles, or derived units (kmol, mmol, etc.). The mole is one of the basic SI units. One mole of any substance corresponds to its quantity, numerically equal to the molecular weight. Therefore, the molecular weight in this case should be considered as a dimensional value with units: g/mol, kg/kmol, kg/mol. So, for example, the molecular weight of nitrogen is 28 g/mol, 28 kg/kmol, but 0.028 kg/mol.
Mass and molar amounts of a substance are related by known relationships
N A \u003d m A / M A; m A = N A M A,
where N A is the amount of component A, mol; m A is the mass of this component, kg;
M A - molecular weight of component A, kg/mol.
In continuous processes, the flow of substance A can be expressed by its mol-
quantity per unit of time
where W A is the molar flow of component A, mol/s; τ - time, s.
For a simple reaction that proceeds almost irreversibly, usually a stoichiomet
ric equation is written in the form
v A A + v B B = v R R + v S S.
However, it is more convenient to write the stoichiometric equation in the form of an algebraic
th, assuming that the stoichiometric coefficients of the reactants are negative, and the reaction products are positive:
Then for each simple reaction we can write the following equalities:
Index "0" refers to the initial amount of the component.
These equalities give grounds to obtain the following material balance equations for the component for a simple reaction:
Example 7.1. The hydrogenation reaction of phenol to cyclohexanol proceeds according to the equation
C 6 H 5 OH + ZN 2 \u003d C 6 H 11 OH, or A + 3B \u003d R.
Calculate the amount of product formed if the initial amount of component A was 235 kg and the final amount was 18.8 kg
Solution: We write the reaction as
R - A - ZV \u003d 0.
The molecular weights of the components are: M A = 94 kg/kmol, M B = 2 kg/kmol and
M R = 100 kg/kmol. Then the molar amounts of phenol at the beginning and at the end of the reaction will be:
N A 0 \u003d 235/94 \u003d 2.5; N A 0 \u003d 18.8 / 94 \u003d 0.2; n \u003d (0.2 - 2.5) / (-1) \u003d 2.3.
The amount of cyclohexanol formed will be equal to
N R = 0 +1∙2.3 = 2.3 kmol or m R = 100∙2.3 = 230 kg.
The determination of stoichiometrically independent reactions in their system in the material and thermal calculations of reaction apparatuses is necessary to exclude reactions that are the sum or difference of some of them. Such an assessment can be most easily carried out using the Gram criterion.
In order not to carry out unnecessary calculations, it should be assessed whether the system is stoichiometrically dependent. For these purposes it is necessary:
Transpose the original matrix of the reaction system;
Multiply the original matrix by the transposed one;
Calculate the determinant of the resulting square matrix.
If this determinant is equal to zero, then the reaction system is stoichiometrically dependent.
Example 7.2. We have a reaction system:
FeO + H 2 \u003d Fe + H 2 O;
Fe 2 O 3 + 3H 2 \u003d 2Fe + 3H 2 O;
FeO + Fe 2 O 3 + 4H 2 \u003d 3Fe + 4H 2 O.
This system is stoichiometrically dependent since the third reaction is the sum of the other two. Let's make a matrix
For each substance in the reaction, there are the following quantities of the substance:
Initial amount of the i-th substance (amount of substance before the start of the reaction);
The final amount of the i-th substance (the amount of the substance at the end of the reaction);
The amount of reacted (for starting substances) or formed substance (for reaction products).
Since the amount of a substance cannot be negative, for the starting substances
Since >.
For reaction products >, therefore, .
Stoichiometric ratios - ratios between quantities, masses or volumes (for gases) of reacting substances or reaction products, calculated on the basis of the reaction equation. Calculations using reaction equations are based on the basic law of stoichiometry: the ratio of the amounts of reacting or formed substances (in moles) is equal to the ratio of the corresponding coefficients in the reaction equation (stoichiometric coefficients).
For the aluminothermic reaction described by the equation:
3Fe 3 O 4 + 8Al = 4Al 2 O 3 + 9Fe,
the amounts of reacted substances and reaction products are related as
For calculations, it is more convenient to use another formulation of this law: the ratio of the amount of a reacted or formed substance as a result of a reaction to its stoichiometric coefficient is a constant for a given reaction.
In general, for a reaction of the form
aA + bB = cC + dD,
where small letters denote coefficients, and large letters - chemical substances, the amounts of reactants are related by the ratio:
Any two terms of this ratio, related by equality, form the proportion of a chemical reaction: for example,
If the mass of the formed or reacted substance of the reaction is known for the reaction, then its amount can be found by the formula
and then, using the proportion of the chemical reaction, can be found for the remaining substances of the reaction. A substance, by mass or quantity of which the masses, quantities or volumes of other participants in the reaction are found, is sometimes called a reference substance.
If the masses of several reagents are given, then the calculation of the masses of the remaining substances is carried out according to the substance that is in short supply, i.e., is completely consumed in the reaction. Amounts of substances that exactly match the reaction equation without excess or deficiency are called stoichiometric quantities.
Thus, in tasks related to stoichiometric calculations, the main action is to find the reference substance and calculate its amount that entered or formed as a result of the reaction.
Calculation of the amount of an individual solid
where is the amount of individual solid A;
Mass of individual solid A, g;
Molar mass of substance A, g/mol.
Calculation of the amount of natural mineral or mixture of solids
Let the natural mineral pyrite be given, the main component of which is FeS 2 . In addition to it, the composition of pyrite includes impurities. The content of the main component or impurities is indicated in mass percent, for example, .
If the content of the main component is known, then
If the content of impurities is known, then
where is the amount of individual substance FeS 2, mol;
Mass of the mineral pyrite, g.
Similarly, the amount of a component in a mixture of solids is calculated if its content in mass fractions is known.
Calculation of the amount of substance of a pure liquid
If the mass is known, then the calculation is similar to the calculation for an individual solid.
If the volume of the liquid is known, then
1. Find the mass of this volume of liquid:
m f = V f s f,
where m W is the mass of liquid g;
V W - volume of liquid, ml;
c w is the density of the liquid, g/ml.
2. Find the number of moles of liquid:
This technique is suitable for any aggregate state of matter.
Determine the amount of substance H 2 O in 200 ml of water.
Solution: if the temperature is not specified, then the density of water is assumed to be 1 g / ml, then:
Calculate the amount of a solute in a solution if its concentration is known
If the mass fraction of the solute, the density of the solution and its volume are known, then
m r-ra \u003d V r-ra s r-ra,
where m p-ra is the mass of the solution, g;
V p-ra - the volume of the solution, ml;
with r-ra - the density of the solution, g / ml.
where is the mass of the dissolved substance, g;
Mass fraction of the dissolved substance, expressed in%.
Determine the amount of nitric acid substance in 500 ml of a 10% acid solution with a density of 1.0543 g/ml.
Determine the mass of the solution
m r-ra \u003d V r-ra s r-ra \u003d 500 1.0543 \u003d 527.150 g
Determine the mass of pure HNO 3
Determine the number of moles of HNO 3
If the molar concentration of the solute and the substance and the volume of the solution are known, then
where is the volume of the solution, l;
Molar concentration of the i-th substance in solution, mol/l.
Calculation of the amount of an individual gaseous substance
If the mass of a gaseous substance is given, then it is calculated by formula (1).
If the volume measured under normal conditions is given, then according to formula (2), if the volume of a gaseous substance is measured under any other conditions, then according to formula (3), the formulas are given on pages 6-7.
The excess air coefficient with this method of organizing the combustion process should correspond to rich mixtures close to stoichiometric. In this case, it will be very difficult to organize efficient combustion of lean mixtures due to the insufficiently high speed of flame front propagation with a high probability of attenuation of ignition sources, significant cyclic non-uniformity of combustion and, ultimately, misfires. Thus, this direction can be called extremely slow combustion of rich gas-air mixtures.[ ...]
The excess air coefficient (a) significantly affects the combustion process and the composition of the combustion products. It is obvious that at a 1.0) it practically does not affect the component composition of flue gases and only leads to a decrease in the concentration of components due to dilution with air not used in the combustion process.[ ...]
Based on the stoichiometric coefficients of the reaction for obtaining dialkylchlorothiophosphate and optimal solution for criterion 2, we impose the restriction X3 = -0.26 (1.087 mol/mol).[ ...]
| 24.5 |
This gives the value of the stoichiometric coefficient for the intake of polyphosphate 1/us,p = g P/g COD(HAc).[ ...]
In table. 24.5 shows the stoichiometric yield factors determined in experiments carried out in pure culture batch reactors. These values are in fairly good agreement, despite various conditions microbiological growth.[ ...]
From expression (3.36) we find the stoichiometric coefficient "sat.r = 0.05 g P / g COD (HAc).[ ...]
[ ...]
From example 3.2, you can find the stoichiometric coefficients of the equation for the removal of acetic acid: 1 mol of HAs (60 g of HAs) requires 0.9 mol of 02 and 0.9 32 = 29 g of 02.[ ...]
| 3.12 |
In these formulas, the first starting material is included in all stoichiometric equations and its stoichiometric coefficient in them is V/, = -1. For this substance, the degrees of transformation lu in each stoichiometric equation are given (all of them - K). In equations (3.14) and (3.15) it is assumed that the i-th component - the product for which selectivity and yield are determined, is formed only in the 1st stoichiometric equation (then E / \u003d x () . The amounts of components in these formulas are measured in moles (designation LO, as is traditionally accepted in the chemical sciences.[ ...]
When compiling redox equations, stoichiometric coefficients are found for the oxidation of the element before and after the reaction. The oxidation of an element in compounds is determined by the number of electrons spent by the atom on the formation of polar and ionic bonds, and the sign of oxidation is determined by the direction of displacement of the binding electron pairs. For example, the oxidation of the sodium ion in the NaCl compound is +1, and that of chlorine is -I.[ ...]
It is more convenient to represent the stoichiometry of a microbiological reaction with a stoichiometric balance equation, rather than in the form of yield factor tables. Such a description of the composition of the components of a microbiological cell required the use of an empirical formula. The formula of the substance of the cell C5H702N was experimentally established, which is often used in the preparation of stoichiometric equations.[ ...]
In table. Figure 3.6 shows typical values for kinetic and other constants, as well as stoichiometric coefficients, for an aerobic urban wastewater treatment process. It should be noted that there is a certain correlation between individual constants, so it is necessary to use a set of constants from one source, and not to select individual constants from different sources. In table. 3.7 shows similar correlations.[ ...]
The method is standardized by known amounts of iodine, converted to ozone, based on a stoichiometric coefficient equal to one (1 mole of ozone releases 1 mole of iodine). This coefficient is supported by the results of a number of studies, on the basis of which the stoichiometric reactions of ozone with olefins were established. With a different coefficient, these results would be difficult to explain. However, in the work it was found that the indicated coefficient is 1.5. This is consistent with the data, according to which a stoichiometric coefficient equal to one is obtained at pH 9, and much more iodine is released in an acidic environment than in a neutral and alkaline one.[ ...]
The tests were carried out at full load and a constant crankshaft speed of 1,500 min1. The excess air coefficient varied in the range of 0.8 [ ...]
Material processes in living nature, the cycles of biogenic elements are associated with energy flows by stoichiometric coefficients that vary in the most diverse organisms only within the same order. At the same time, thanks to high efficiency catalysis, the energy costs for the synthesis of new substances in organisms are much less than in the technical analogues of these processes.[ ...]
Measurements of engine characteristics and emissions of harmful emissions for all combustion chambers were carried out in a wide range of changes in the excess air coefficient from a stoichiometric value to an extremely lean mixture. On fig. 56 and 57 show the main results depending on a, obtained at a speed of 2000 min and a wide open throttle. The value of the ignition advance angle was chosen from the condition of obtaining the maximum torque.[ ...]
The biological process of phosphorus removal is complex, so, of course, our approach is greatly simplified. In table. 8.1 presents a set of stoichiometric coefficients describing the processes occurring with the participation of FAO. The table looks complicated, but simplifications have already been made in it.[ ...]
In one of the latest works, it is assumed that 1 mol of NO2 gives 0.72 g-ion of NO7. According to data provided by the International Organization for Standardization, the stoichiometric coefficient depends on the composition of the Griess-type reagents. Six variants of this reagent are proposed, differing in the composition of its components, and it is indicated that the absorption efficiency for all types of absorption solutions is 90%, and the stoichiometric coefficient, taking into account the absorption efficiency, varies from 0.8 to 1. Reducing the amount of NEDA and replacing sulfanilic acid with sulfanilamide (white streptocide) gives a greater value of this coefficient. The authors of the work explain this by the loss of HN02 due to the formation of NO during side reactions.[ ...]
When designing biochemical treatment facilities Wastewater and the analysis of their work, the following calculation parameters are usually used: the rate of biological oxidation, stoichiometric coefficients for electron acceptors, growth rate and physical properties activated sludge biomass. The study of chemical changes in connection with biological transformations occurring in a bioreactor makes it possible to obtain a fairly complete picture of the structure's operation. For anaerobic systems, which include anaerobic filters, such information is needed to ensure the optimal pH value of the environment, which is the main factor in the normal operation of treatment facilities. In some aerobic systems, such as those in which nitrification occurs, control of the pH of the medium is also necessary to ensure optimal microbial growth rates. For closed treatment facilities that came into practice at the end of the 60s, which use pure oxygen (oxy-tank), the study chemical interactions has become necessary not only for pH control, but also for the engineering calculation of gas pipeline equipment.[ ...]
The catalytic conversion rate constant k in the general case at a given temperature is a function of the rate constants of the direct, reverse, and side reactions, as well as the diffusion coefficients of the initial reagents and their interaction products. The rate of a heterogeneous catalytic process is determined, as noted above, by the relative rates of its individual stages and is limited by the slowest of them. As a result, the order of the catalytic reaction almost never coincides with the molecularity of the reaction corresponding to the stoichiometric ratio in the equation for this reaction, and the expressions for calculating the rate constant of the catalytic conversion are specific for specific stages and conditions for its implementation.[ ...]
To control the neutralization reaction, one must know how much acid or base to add to the solution to obtain the desired pH value. To solve this problem, the method of empirical evaluation of stoichiometric coefficients can be used, which is carried out using titration.[ ...]
The equilibrium composition of the combustion products in the chamber is determined by the law of mass action. According to this law, the rate of chemical reactions is directly proportional to the concentration of the initial reagents, each of which is taken to a degree equal to the stoichiometric coefficient with which the substance enters the chemical reaction equation. Based on the composition of the fuels, we can assume that the products of combustion, for example, liquid rocket fuels in the chamber will consist of CO2, H20, CO, NO, OH, N2, H2, N. H, O, for solid rocket fuel- from A1203, N2, H2, HC1, CO, CO2, H20 at T \u003d 1100 ... 2200 K. [ ...]
To substantiate the possibility of using two-stage combustion of natural gas, experimental studies of the distribution of local temperatures, concentrations of nitrogen oxides and combustible substances along the length of the flame depending on the coefficient of excess air supplied through the burner were carried out. The experiments were carried out with the combustion of natural gas in the furnace of a PTVM-50 boiler equipped with a VTI vortex burner with peripheral gas jet discharge into a swirling transverse air flow. It has been established that at ag O.wb the process of fuel burn-up ends at a distance 1f/X>out = 4.2, and at ag = 1.10 - at a distance bf10out = 3.6. This indicates the prolongation of the combustion process under conditions significantly different from stoichiometric ones.[ ...]
A simplified matrix of process parameters with activated sludge without nitrification is presented in Table. 4.2. It is assumed here that three main factors contribute to the conversion process: biological growth, degradation, and hydrolysis. The reaction rates are indicated in the right column, and the coefficients presented in the table are stoichiometric. Using the table data, one can write the mass balance equation, for example, for the easily decomposable organic matter Bae in a perfectly stirred reactor. The expressions responsible for the transport need no explanation. We find two expressions describing the transformations of a substance by multiplying the stoichiometric coefficients from (in this case) "component" columns by the corresponding reaction rates from the right column of Table. 4.2.[ ...]
On fig. 50 shows the change in the content of Wx in the combustion products (g / kWh) depending on the composition of the mixture and the ignition timing. Because the formation of NOx largely depends on the gas temperature, with early ignition, the emission of NOx increases. The dependence of the formation of 1 Ux on the coefficient of excess air is more complex, because There are two opposing factors. The formation of 1NHOx depends on the oxygen concentration in the combustible mixture and the temperature. Leaning the mixture increases the oxygen concentration but reduces the maximum combustion temperature. This leads to the fact that the maximum content is achieved when working with mixtures slightly poorer than stoichiometric. At the same values of the excess air coefficient, the effective efficiency has a maximum.[ ...]
On fig. Figure 7.2 shows the experimental dependences of the methanol concentration on the NO3-N concentration at the outlet of the complete displacement biofilter. The lines connecting the experimental points characterize the distribution of the substance along the filter at different Smc/Sn ratios. The slope of the curves corresponds to the value of the stoichiometric coefficient: 3.1 kg CH3OH/kg NO -N.
The relation connecting the concentrations of the reacting substances with the equilibrium constant is a mathematical expression of the law of mass action, which can be formulated as follows: for a given reversible reaction in a state of chemical equilibrium, the ratio of the product of the equilibrium concentrations of the reaction products to the product of the equilibrium concentrations of the starting substances at a given temperature is a constant value, and the concentration of each substance must be raised to the power of its stoichiometric coefficient.[ ...]
In the Soviet Union, the method of Polezhaev and Girina is used to determine NO¡¡ in the atmosphere. This method uses an 8% solution of KJ to capture nitrogen dioxide. The determination of nitrite ions in the resulting solution is carried out using the Griess-Ilosvay reagent. Potassium iodide solution is a much more effective NO2 absorber than alkali solution. With its volume (only 6 ml) and air flow rate (0.25 l / min), no more than 2% NO2 slips through the absorption device with a porous glass plate. The selected samples are well preserved (about a month). The stoichiometric coefficient for the absorption of NOa by the KJ solution is 0.75, taking into account the breakthrough. According to our data, NO does not interfere with this method at a ratio of NO: NOa concentrations of 3: 1.[ ...]
The disadvantages of this method, widely introduced into the practice of high-temperature waste processing, is the need to use expensive alkaline reagents (NaOH and Na2CO3). In this way, it is possible to meet the needs of many industries that need to neutralize small amounts of liquid waste with a wide range of components. chemical composition and any content of organochlorine compounds. However, the combustion of chlorine-containing solvents should be approached with caution, since under certain conditions (1 > 1200 ° C, excess air coefficient > 1.5), exhaust gases may contain phosgene - highly toxic carbon chlorine, or carbonic acid chloride (COC12). The life-threatening concentration of this substance is 450 mg per 1 m3 of air.[ ...]
The processes of leaching or chemical weathering of sparingly soluble minerals or their associations are characterized by the formation of new solid phases; equilibria between them and dissolved components are analyzed using thermodynamic state diagrams. Fundamental difficulties here usually arise in connection with the need to describe the kinetics of processes, without which their consideration is often not justified. The corresponding kinetic models require the reflection of chemical interactions in an explicit form - through the partial concentrations of the reactants cx, taking into account the stoichiometric coefficients V. of specific reactions.
