Studying the parameters of a system, including starting materials and reaction products, makes it possible to find out which factors shift chemical equilibrium and lead to the desired changes. Based on the conclusions of Le Chatelier, Brown and other scientists about methods of carrying out reversible reactions industrial technologies, making it possible to carry out processes that previously seemed impossible and obtain economic benefits.
Variety of chemical processes
Based on the characteristics of the thermal effect, many reactions are classified as exo- or endothermic. The first come with the formation of heat, for example, the oxidation of carbon, the hydration of concentrated sulfuric acid. The second type of change is associated with the absorption of thermal energy. Examples of endothermic reactions: decomposition of calcium carbonate with the formation of slaked lime and carbon dioxide, formation of hydrogen and carbon during the thermal decomposition of methane. In the equations of exo- and endothermic processes, it is necessary to indicate the thermal effect. The redistribution of electrons between the atoms of the reacting substances occurs in redox reactions. Four types of chemical processes are distinguished according to the characteristics of the reagents and products:
To characterize the processes, the completeness of the interaction of the reacting compounds is important. This feature underlies the division of reactions into reversible and irreversible.
Reversibility of reactions
Reversible processes make up the majority of chemical phenomena. Education final products of the reactants is a direct reaction. In the reverse case, the starting substances are obtained from the products of their decomposition or synthesis. In the reacting mixture, a chemical equilibrium arises in which the same number of compounds is obtained as the original molecules decompose. In reversible processes, instead of the “=” sign between reactants and products, the symbols “↔” or “⇌” are used. The arrows may be unequal in length, which is due to the dominance of one of the reactions. In chemical equations, you can indicate the aggregate characteristics of substances (g - gases, g - liquids, t - solids). Huge practical significance have scientifically proven methods of influencing reversible processes. Thus, the production of ammonia became profitable after creating conditions that shifted the equilibrium towards the formation of the target product: 3H 2 (g) + N 2 (g) ⇌ 2NH 3 (g). Irreversible phenomena lead to the appearance of an insoluble or slightly soluble compound and the formation of a gas that leaves the reaction sphere. Such processes include ion exchange and the breakdown of substances.
Chemical equilibrium and conditions for its displacement
The characteristics of the forward and reverse processes are influenced by several factors. One of them is time. The concentration of the substance taken for the reaction gradually decreases, and the final compound increases. The forward reaction is slower and slower, while the reverse process is gaining speed. At a certain interval, two opposing processes occur synchronously. Interactions between substances occur, but concentrations do not change. The reason is the dynamic chemical equilibrium established in the system. Its preservation or change depends on:
- temperature conditions;
- concentrations of compounds;
- pressure (for gases).
Chemical equilibrium shift
In 1884, the outstanding scientist from France A.L. Le Chatelier proposed a description of ways to remove a system from a state of dynamic equilibrium. The method is based on the principle of leveling the action external factors. Le Chatelier noticed that processes arise in the reacting mixture that compensate for the influence of extraneous forces. The principle formulated by the French researcher states that a change in conditions in a state of equilibrium favors the occurrence of a reaction that weakens external influences. The equilibrium shift obeys this rule; it is observed when the composition changes, temperature conditions and pressure. Technologies based on the findings of scientists are used in industry. Many chemical processes, which were considered practically impracticable, are carried out thanks to methods of shifting the equilibrium.
Effect of concentration
A shift in equilibrium occurs if certain components are removed from the interaction zone or additional portions of the substance are introduced. Removing products from the reaction mixture usually causes an increase in the rate of their formation; adding substances, on the contrary, leads to their preferential decomposition. In the esterification process, sulfuric acid is used for dehydration. When it is introduced into the reaction sphere, the yield of methyl acetate increases: CH 3 COOH + CH 3 OH ↔ CH 3 COOCH 3 + H 2 O. If you add oxygen that interacts with sulfur dioxide, the chemical equilibrium shifts towards the direct reaction of the formation of sulfur trioxide. Oxygen binds into SO 3 molecules, its concentration decreases, which is consistent with Le Chatelier's rule for reversible processes.
Temperature change
Processes that involve the absorption or release of heat are endothermic and exothermic. To shift the equilibrium, heating or heat removal from the reacting mixture is used. An increase in temperature is accompanied by an increase in the rate of endothermic phenomena, in which additional energy is absorbed. Cooling leads to the advantage of exothermic processes that occur with the release of heat. When carbon dioxide interacts with coal, heating is accompanied by an increase in the concentration of monoxide, and cooling leads to the predominant formation of soot: CO 2 (g) + C (t) ↔ 2CO (g).
Effect of pressure
Pressure change - important factor for reacting mixtures including gaseous compounds. You should also pay attention to the difference in volumes of the starting and resulting substances. A decrease in pressure leads to a preferential occurrence of phenomena in which the total volume of all components increases. An increase in pressure directs the process towards a decrease in the volume of the entire system. This pattern is observed in the reaction of ammonia formation: 0.5N 2 (g) + 1.5 N 2 (g) ⇌ NH 3 (g). A change in pressure will not affect the chemical equilibrium in those reactions that occur at a constant volume.
Optimal conditions for the chemical process
Creating conditions for shifting the balance largely determines the development of modern chemical technologies. Practical use scientific theory contributes to optimal production results. The most striking example is the production of ammonia: 0.5N 2 (g) + 1.5 N 2 (g) ⇌ NH 3 (g). An increase in the content of N 2 and H 2 molecules in the system is favorable for the synthesis of complex substances from simple ones. The reaction is accompanied by the release of heat, so a decrease in temperature will cause an increase in the concentration of NH 3. The volume of the initial components is greater than the target product. An increase in pressure will ensure an increase in the yield of NH 3.
Under production conditions, the optimal ratio of all parameters (temperature, concentration, pressure) is selected. In addition, the contact area between the reagents is of great importance. In solid heterogeneous systems, an increase in surface area leads to an increase in the reaction rate. Catalysts increase the rate of forward and reverse reactions. The use of substances with such properties does not lead to a shift in chemical equilibrium, but accelerates its onset.
Main article: Le Chatelier-Brown principle
The position of chemical equilibrium depends on the following reaction parameters: temperature, pressure and concentration. The influence that these factors have on a chemical reaction is subject to the pattern that was expressed in general view in 1885 by the French scientist Le Chatelier.
Factors influencing chemical equilibrium:
1) temperature
As the temperature increases, the chemical equilibrium shifts towards the endothermic (absorption) reaction, and when it decreases, towards the exothermic (release) reaction.
CaCO 3 =CaO+CO 2 -Q t →, t↓ ←
N 2 +3H 2 ↔2NH 3 +Q t ←, t↓ →
2) pressure
As pressure increases, the chemical equilibrium shifts towards a smaller volume of substances, and as pressure decreases towards a larger volume. This principle only applies to gases, i.e. If solids are involved in the reaction, they are not taken into account.
CaCO 3 =CaO+CO 2 P ←, P↓ →
1mol=1mol+1mol
3) concentration of starting substances and reaction products
With an increase in the concentration of one of the starting substances, the chemical equilibrium shifts towards the reaction products, and with an increase in the concentration of the reaction products, towards the starting substances.
S 2 +2O 2 =2SO 2 [S],[O] →, ←
Catalysts do not affect the shift of chemical equilibrium!
Basic quantitative characteristics of chemical equilibrium: chemical equilibrium constant, degree of conversion, degree of dissociation, equilibrium yield. Explain the meaning of these quantities using the example of specific chemical reactions.
In chemical thermodynamics, the law of mass action relates the equilibrium activities of the starting substances and reaction products, according to the relationship:
Activity of substances. Instead of activity, concentration (for a reaction in an ideal solution), partial pressures (a reaction in a mixture of ideal gases), fugacity (a reaction in a mixture of real gases) can be used;
Stoichiometric coefficient (negative for starting substances, positive for products);
Chemical equilibrium constant. The subscript "a" here means the use of the activity value in the formula.
The efficiency of a reaction is usually assessed by calculating the yield of the reaction product (section 5.11). At the same time, the efficiency of the reaction can also be assessed by determining what part of the most important (usually the most expensive) substance was converted into the target reaction product, for example, what part of SO 2 was converted into SO 3 during the production of sulfuric acid, that is, find degree of conversion original substance.
Let a brief diagram of the ongoing reaction
Then the degree of conversion of substance A into substance B (A) is determined by the following equation
Where n proreact (A) – the amount of substance of reagent A that reacted to form product B, and n initial (A) – initial amount of reagent A. 
Naturally, the degree of transformation can be expressed not only in terms of the amount of a substance, but also in terms of any quantities proportional to it: the number of molecules (formula units), mass, volume.
If reagent A is taken in short supply and the loss of product B can be neglected, then the degree of conversion of reagent A is usually equal to the yield of product B
The exception is reactions in which the starting substance is obviously consumed to form several products. So, for example, in the reaction
Cl 2 + 2KOH = KCl + KClO + H 2 O
chlorine (reagent) is converted equally into potassium chloride and potassium hypochlorite. In this reaction, even with a 100% yield of KClO, the degree of conversion of chlorine into it is 50%.
The quantity you know - the degree of protolysis (section 12.4) - is a special case of the degree of conversion:
Within the framework of TED, similar quantities are called degree of dissociation acids or bases (also designated as the degree of protolysis). The degree of dissociation is related to the dissociation constant according to Ostwald's dilution law.
Within the framework of the same theory, the hydrolysis equilibrium is characterized by degree of hydrolysis (h), and the following expressions are used that relate it to the initial concentration of the substance ( With) and dissociation constants of weak acids (K HA) and weak bases formed during hydrolysis ( K MOH):
The first expression is valid for the hydrolysis of a salt of a weak acid, the second - salts of a weak base, and the third - salts of a weak acid and a weak base. All these expressions can only be used for dilute solutions with a degree of hydrolysis of no more than 0.05 (5%).
Typically, the equilibrium yield is determined by a known equilibrium constant, with which it is related in each specific case by a certain ratio.
The yield of the product can be changed by shifting the equilibrium of the reaction in reversible processes, under the influence of factors such as temperature, pressure, concentration.
In accordance with Le Chatelier's principle, the equilibrium degree of conversion increases with increasing pressure during simple reactions, and in other cases the volume of the reaction mixture does not change and the yield of the product does not depend on pressure.
The effect of temperature on the equilibrium yield, as well as on the equilibrium constant, is determined by the sign of the thermal effect of the reaction.
For a more complete assessment of reversible processes, the so-called yield from the theoretical (yield from the equilibrium) is used, equal to the ratio of the actually obtained product to the amount that would be obtained in a state of equilibrium.
THERMAL DISSOCIATION chemical
a reaction of reversible decomposition of a substance caused by an increase in temperature.
With Etc., several (2H2H+ OCaO + CO) or one simpler substance are formed from one substance
Equilibrium etc. is established according to the law of mass action. It
can be characterized either by an equilibrium constant or by the degree of dissociation
(the ratio of the number of decayed molecules to the total number of molecules). IN
In most cases, etc. is accompanied by the absorption of heat (increase
enthalpy
DN>0); therefore, in accordance with Le Chatelier-Brown principle
heating enhances it, the degree of displacement etc. with temperature is determined
absolute value of DN. The pressure interferes with etc., the more strongly, the greater
change (increase) in the number of moles (Di) of gaseous substances
the degree of dissociation does not depend on pressure. If solids are not
form solid solutions and are not in a highly dispersed state,
then the pressure etc. is uniquely determined by the temperature. To implement T.
d. solids (oxides, crystalline hydrates, etc.)
It is important to know
temperature at which the dissociation pressure becomes equal to the external one (in particular,
atmospheric) pressure. Since the gas released can overcome
ambient pressure, then upon reaching this temperature the decomposition process
immediately intensifies.
Dependence of the degree of dissociation on temperature: the degree of dissociation increases with increasing temperature (increasing temperature leads to an increase in the kinetic energy of dissolved particles, which promotes the disintegration of molecules into ions) 
The degree of conversion of starting substances and the equilibrium yield of the product. Methods for their calculation at a given temperature. What data is needed for this? Give a scheme for calculating any of these quantitative characteristics of chemical equilibrium using an arbitrary example.
The degree of conversion is the amount of reacted reagent divided by its original amount. For the simplest reaction, where is the concentration at the inlet to the reactor or at the beginning of the periodic process, is the concentration at the outlet of the reactor or the current moment of the periodic process. For a voluntary response, for example, 
, in accordance with the definition, the calculation formula is the same: . If there are several reagents in a reaction, then the degree of conversion can be calculated for each of them, for example, for the reaction 
The dependence of the degree of conversion on the reaction time is determined by the change in the concentration of the reagent over time. At the initial moment of time, when nothing has transformed, the degree of transformation is zero. Then, as the reagent is converted, the degree of conversion increases. For an irreversible reaction, when nothing prevents the reagent from being completely consumed, its value tends (Fig. 1) to unity (100%). 
Fig. 1 The greater the rate of reagent consumption, determined by the value of the rate constant, the faster the degree of conversion increases, as shown in the figure. If the reaction is reversible, then as the reaction tends to equilibrium, the degree of conversion tends to an equilibrium value, the value of which depends on the ratio of the rate constants of the forward and reverse reactions (on the equilibrium constant) (Fig. 2). 
Fig. 2 Yield of the target product Yield of the product is the amount of the target product actually obtained, divided by the amount of this product that would have been obtained if all the reagent had passed into this product (to the maximum possible amount of the resulting product). Or (through the reagent): the amount of the reagent actually converted into the target product, divided by the initial amount of the reagent. For the simplest reaction, the yield is , and keeping in mind that for this reaction, 
, i.e. For the simplest reaction, the yield and the degree of conversion are the same value. If the transformation takes place with a change in the amount of substances, for example, then, in accordance with the definition, the stoichiometric coefficient must be included in the calculated expression. In accordance with the first definition, the imaginary amount of product obtained from the entire initial amount of the reagent will be for this reaction two times less than the initial amount of the reagent, i.e. , And calculation formula. In accordance with the second definition, the amount of the reagent actually transferred into the target product will be twice as large as this product was formed, i.e. , then the calculation formula is . Naturally, both expressions are the same. For a more complex reaction, the calculation formulas are written in exactly the same way in accordance with the definition, but in this case the output is no longer equal to the power transformations. For example, for the reaction, 
. If there are several reagents in a reaction, the yield can be calculated for each of them; if there are also several target products, then the yield can be calculated for any target product for any reagent. As can be seen from the structure of the calculation formula (the denominator contains a constant value), the dependence of the yield on the reaction time is determined by the time dependence of the concentration of the target product. So, for example, for the reaction 
this dependence looks like in Fig. 3. 
Fig.3
The degree of conversion as a quantitative characteristic of chemical equilibrium. How will an increase in total pressure and temperature affect the degree of conversion of the reagent ... in a gas-phase reaction: ( the equation is given)? Provide a rationale for your answer and appropriate mathematical expressions.
Reversibility of chemicals. reactions. Chemical equilibrium and conditions for its displacement, practical application.
All chemical reactions can be divided into reversible and irreversible.
Reversible reactions do not proceed completely: In a reversible reaction, none of the reactants are completely consumed. A reversible reaction can occur in both forward and reverse directions. Reversible chemical reactions are written as one chemical equation with a reversibility sign: .
A reaction going from left to right is called straight reaction, and from right to left - reverse .
Majority chemical reactions reversible. For example, a reversible reaction is the interaction of hydrogen with iodine vapor:
Initially, when the starting materials are mixed, the rate of the forward reaction is high, and the rate of the reverse reaction is zero. As the reaction proceeds, the starting substances are consumed and their concentrations fall. As a result, the rate of the forward reaction decreases. At the same time, reaction products appear and their concentration increases. Therefore, a reverse reaction begins to occur, and its speed gradually increases. When the rates of forward and reverse reactions become equal, chemical balance.
The state of chemical equilibrium is influenced by: 1) concentration of substances
2) temperature
3) pressure
When one of these parameters changes, the chemical equilibrium is disrupted and the concentrations of all reacting substances will change until a new equilibrium is established. Such a transition of a system from one state to another is called displacement. The direction of displacement of chemical equilibrium is determined by the principle
Le Chatelier: " If any influence is exerted on a system that is in chemical equilibrium, then as a result of the processes occurring in it, the equilibrium will shift in such a direction that the effect will decrease.". For example, when one of the substances participating in the reaction is introduced into the system, the equilibrium shifts towards the consumption of this substance. As the pressure increases, it shifts so that the pressure in the system decreases. As the temperature rises, the equilibrium shifts towards the endothermic reaction, the temperature in the system drops.
Irreversible reactions are those that proceed to completion. – until one of the reactants is completely consumed. Conditions for the irreversibility of chemical reactions:
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Chemical equilibrium and principles of its displacement (Le Chatelier's principle)
In reversible reactions, under certain conditions, a state of chemical equilibrium may occur. This is a condition in which the rate of the reverse reaction becomes equal to the rate of the forward reaction. But in order to shift the equilibrium in one direction or another, it is necessary to change the conditions for the reaction. The principle of shifting equilibrium is Le Chatelier's principle.
Key points:
1. An external influence on a system that is in a state of equilibrium leads to a shift in this equilibrium in a direction in which the effect of the effect is weakened.
2. When the concentration of one of the reacting substances increases, the equilibrium shifts towards the consumption of this substance; when the concentration decreases, the equilibrium shifts towards the formation of this substance.
3. With increasing pressure, the equilibrium shifts towards decreasing quantity gaseous substances, that is, in the direction of decreasing pressure; when the pressure decreases, the equilibrium shifts towards increasing amounts of gaseous substances, that is, towards increasing pressure. If the reaction proceeds without changing the number of molecules of gaseous substances, then pressure does not affect the equilibrium position in this system.
4. When the temperature increases, the equilibrium shifts towards the endothermic reaction, and when the temperature decreases, towards the exothermic reaction.
For the principles we thank the manual “Beginnings of Chemistry” Kuzmenko N.E., Eremin V.V., Popkov V.A.
Unified State Examination tasks on chemical equilibrium (formerly A21)
Task No. 1.
H2S(g) ↔ H2(g) + S(g) - Q
1. Increased pressure
2. Rising temperature
3. Decreased pressure
Explanation: First, let's consider the reaction: all substances are gases and on the right side there are two molecules of products, and on the left there is only one, the reaction is also endothermic (-Q). Therefore, let us consider the change in pressure and temperature. We need the equilibrium to shift towards the reaction products. If we increase the pressure, then the equilibrium will shift towards decreasing volume, that is, towards the reactants - this does not suit us. If we increase the temperature, then the equilibrium will shift towards the endothermic reaction, in our case towards the products, which is what was required. The correct answer is 2.
Task No. 2.
Chemical equilibrium in the system
SO3(g) + NO(g) ↔ SO2(g) + NO2(g) - Q
will shift towards the formation of reagents when:
1. Increasing NO concentration
2. Increasing SO2 concentration
3. Temperature rises
4. Increased pressure
Explanation: all substances are gases, but the volumes on the right and left sides of the equation are the same, so pressure will not affect the equilibrium in the system. Consider a change in temperature: as the temperature increases, the equilibrium shifts towards the endothermic reaction, precisely towards the reactants. The correct answer is 3.
Task No. 3.
In system
2NO2(g) ↔ N2O4(g) + Q
a shift of balance to the left will contribute
1. Increase in pressure
2. Increase in N2O4 concentration
3. Temperature drop
4. Introduction of catalyst
Explanation: Let us pay attention to the fact that the volumes of gaseous substances on the right and left sides of the equation are not equal, therefore a change in pressure will affect the equilibrium in this system. Namely, with increasing pressure, the equilibrium shifts towards a decrease in the amount of gaseous substances, that is, to the right. This doesn't suit us. The reaction is exothermic, therefore a change in temperature will affect the equilibrium of the system. As the temperature decreases, the equilibrium will shift towards the exothermic reaction, that is, also to the right. As the concentration of N2O4 increases, the equilibrium shifts towards the consumption of this substance, that is, to the left. The correct answer is 2.
Task No. 4.
In reaction
2Fe(s) + 3H2O(g) ↔ 2Fe2O3(s) + 3H2(g) - Q
the equilibrium will shift towards the reaction products when
1. Increased pressure
2. Adding a catalyst
3. Adding iron
4. Adding water
Explanation: the number of molecules in the right and left parts is the same, so a change in pressure will not affect the equilibrium in this system. Let's consider an increase in the concentration of iron - the equilibrium should shift towards the consumption of this substance, that is, to the right (towards the reaction products). The correct answer is 3.
Task No. 5.
Chemical equilibrium
H2O(l) + C(t) ↔ H2(g) + CO(g) - Q
will shift towards the formation of products in the case
1. Increased pressure
2. Increase in temperature
3. Increasing the process time
4. Catalyst Applications
Explanation: a change in pressure will not affect the equilibrium in a given system, since not all substances are gaseous. As the temperature increases, the equilibrium shifts towards the endothermic reaction, that is, to the right (towards the formation of products). The correct answer is 2.
Task No. 6.
As the pressure increases, the chemical equilibrium will shift towards the products in the system:
1. CH4(g) + 3S(s) ↔ CS2(g) + 2H2S(g) - Q
2. C(t) + CO2(g) ↔ 2CO(g) - Q
3. N2(g) + 3H2(g) ↔ 2NH3(g) + Q
4. Ca(HCO3)2(t) ↔ CaCO3(t) + CO2(g) + H2O(g) - Q
Explanation: reactions 1 and 4 are not affected by changes in pressure, because not all participating substances are gaseous; in equation 2, the number of molecules on the right and left sides is the same, so pressure will not affect. Equation 3 remains. Let's check: with increasing pressure, the equilibrium should shift towards decreasing amounts of gaseous substances (4 molecules on the right, 2 molecules on the left), that is, towards the reaction products. The correct answer is 3.
Task No. 7.
Does not affect balance shift
H2(g) + I2(g) ↔ 2HI(g) - Q
1. Increasing pressure and adding catalyst
2. Raising the temperature and adding hydrogen
3. Lowering the temperature and adding hydrogen iodide
4. Adding iodine and adding hydrogen
Explanation: in the right and left parts the amounts of gaseous substances are the same, so a change in pressure will not affect the equilibrium in the system, and adding a catalyst will also not affect it, because as soon as we add a catalyst, the direct reaction will accelerate, and then immediately the reverse and equilibrium in the system will be restored . The correct answer is 1.
Task No. 8.
To shift the equilibrium in a reaction to the right
2NO(g) + O2(g) ↔ 2NO2(g); ΔH°<0
required
1. Introduction of catalyst
2. Lowering the temperature
3. Lower pressure
4. Decreased oxygen concentration
Explanation: a decrease in oxygen concentration will lead to a shift in equilibrium towards the reactants (to the left). A decrease in pressure will shift the equilibrium towards a decrease in the amount of gaseous substances, that is, to the right. The correct answer is 3.
Task No. 9.
Product yield in an exothermic reaction
2NO(g) + O2(g) ↔ 2NO2(g)
with a simultaneous increase in temperature and decrease in pressure
1. Increase
2. Will decrease
3. Will not change
4. First it will increase, then it will decrease
Explanation: when the temperature increases, the equilibrium shifts towards the endothermic reaction, that is, towards the products, and when the pressure decreases, the equilibrium shifts towards an increase in the amounts of gaseous substances, that is, also to the left. Therefore, the product yield will decrease. The correct answer is 2.
Task No. 10.
Increasing the yield of methanol in the reaction
CO + 2H2 ↔ CH3OH + Q
promotes
1. Increase in temperature
2. Introduction of catalyst
3. Introduction of inhibitor
4. Increased pressure
Explanation: with increasing pressure, the equilibrium shifts towards the endothermic reaction, that is, towards the reactants. An increase in pressure shifts the equilibrium towards decreasing amounts of gaseous substances, that is, towards the formation of methanol. The correct answer is 4.
Tasks for independent solution (answers below)
1. In the system
CO(g) + H2O(g) ↔ CO2(g) + H2(g) + Q
a shift in chemical equilibrium towards reaction products will be facilitated by
1. Reducing pressure
2. Increase in temperature
3. Increase in carbon monoxide concentration
4. Increase in hydrogen concentration
2. In which system, when pressure increases, does the equilibrium shift towards the reaction products?
1. 2СО2(g) ↔ 2СО2(g) + O2(g)
2. C2H4(g) ↔ C2H2(g) + H2(g)
3. PCl3(g) + Cl2(g) ↔ PCl5(g)
4. H2(g) + Cl2(g) ↔ 2HCl(g)
3. Chemical equilibrium in the system
2HBr(g) ↔ H2(g) + Br2(g) - Q
will shift towards the reaction products when
1. Increased pressure
2. Rising temperature
3. Decreased pressure
4. Using a catalyst
4. Chemical equilibrium in the system
C2H5OH + CH3COOH ↔ CH3COOC2H5 + H2O + Q
shifts towards the reaction products when
1. Adding water
2. Reducing the concentration of acetic acid
3. Increasing ether concentration
4. When removing ester
5. Chemical equilibrium in the system
2NO(g) + O2(g) ↔ 2NO2(g) + Q
shifts towards the formation of the reaction product when
1. Increased pressure
2. Rising temperature
3. Decreased pressure
4. Application of catalyst
6. Chemical equilibrium in the system
CO2(g) + C(s) ↔ 2СО(g) - Q
will shift towards the reaction products when
1. Increased pressure
2. Lowering the temperature
3. Increasing CO concentration
4. Temperature rises
7. Changes in pressure will not affect the state of chemical equilibrium in the system
1. 2NO(g) + O2(g) ↔ 2NO2(g)
2. N2(g) + 3H2(g) ↔ 2NH3(g)
3. 2CO(g) + O2(g) ↔ 2CO2(g)
4. N2(g) + O2(g) ↔ 2NO(g)
8. In which system, with increasing pressure, will the chemical equilibrium shift towards the starting substances?
1. N2(g) + 3H2(g) ↔ 2NH3(g) + Q
2. N2O4(g) ↔ 2NO2(g) - Q
3. CO2(g) + H2(g) ↔ CO(g) + H2O(g) - Q
4. 4HCl(g) + O2(g) ↔ 2H2O(g) + 2Cl2(g) + Q
9. Chemical equilibrium in the system
С4Н10(g) ↔ С4Н6(g) + 2Н2(g) - Q
will shift towards the reaction products when
1. Increase in temperature
2. Lowering the temperature
3. Using a catalyst
4. Reducing butane concentration
10. On the state of chemical equilibrium in the system
H2(g) + I2(g) ↔ 2HI(g) -Q
does not affect
1. Increase in pressure
2. Increasing iodine concentration
3. Increase in temperature
4. Reduce temperature
2016 assignments
1. Establish a correspondence between the equation of a chemical reaction and the shift in chemical equilibrium with increasing pressure in the system.
Reaction equation Shift of chemical equilibrium
A) N2(g) + O2(g) ↔ 2NO(g) - Q 1. Shifts towards the direct reaction
B) N2O4(g) ↔ 2NO2(g) - Q 2. Shifts towards the reverse reaction
B) CaCO3(s) ↔ CaO(s) + CO2(g) - Q 3. There is no shift in equilibrium
D) Fe3O4(s) + 4CO(g) ↔ 3Fe(s) + 4CO2(g) + Q
2. Establish a correspondence between external influences on the system:
CO2(g) + C(s) ↔ 2СО(g) - Q
and a shift in chemical equilibrium.
A. Increase in CO concentration 1. Shifts towards the direct reaction
B. Decrease in pressure 3. No shift in equilibrium occurs
3. Establish a correspondence between external influences on the system
HCOOH(l) + C5H5OH(l) ↔ HCOOC2H5(l) + H2O(l) + Q
External influence Shift in chemical equilibrium
A. Addition of HCOOH 1. Shifts towards the direct reaction
B. Dilution with water 3. No shift in equilibrium occurs
D. Increase in temperature
4. Establish a correspondence between external influences on the system
2NO(g) + O2(g) ↔ 2NO2(g) + Q
and a shift in chemical equilibrium.
External influence Shift in chemical equilibrium
A. Decrease in pressure 1. Shifts towards the forward reaction
B. Increase in temperature 2. Shifts towards the reverse reaction
B. Increase in NO2 temperature 3. No equilibrium shift occurs
D. Addition of O2
5. Establish a correspondence between external influences on the system
4NH3(g) + 3O2(g) ↔ 2N2(g) + 6H2O(g) + Q
and a shift in chemical equilibrium.
External influence Shift in chemical equilibrium
A. Decrease in temperature 1. Shift towards direct reaction
B. Increase in pressure 2. Shifts towards the reverse reaction
B. Increase in concentration in ammonia 3. No shift in equilibrium occurs
D. Removal of water vapor
6. Establish a correspondence between external influences on the system
WO3(s) + 3H2(g) ↔ W(s) + 3H2O(g) +Q
and a shift in chemical equilibrium.
External influence Shift in chemical equilibrium
A. Increase in temperature 1. Shifts towards a direct reaction
B. Increase in pressure 2. Shifts towards the reverse reaction
B. Use of a catalyst 3. There is no shift in equilibrium
D. Removal of water vapor
7. Establish a correspondence between external influences on the system
С4Н8(g) + Н2(g) ↔ С4Н10(g) + Q
and a shift in chemical equilibrium.
External influence Shift in chemical equilibrium
A. Increase in hydrogen concentration 1. Shifts towards a direct reaction
B. Increase in temperature 2. Shifts towards the reverse reaction
B. Increase in pressure 3. No shift in equilibrium occurs
D. Use of a catalyst
8. Establish a correspondence between the equation of a chemical reaction and a simultaneous change in the parameters of the system, leading to a shift in the chemical equilibrium towards a direct reaction.
Reaction equation Changing system parameters
A. H2(g) + F2(g) ↔ 2HF(g) + Q 1. Increase in temperature and hydrogen concentration
B. H2(g) + I2(s) ↔ 2HI(g) -Q 2. Decrease in temperature and hydrogen concentration
B. CO(g) + H2O(g) ↔ CO2(g) + H2(g) + Q 3. Increasing temperature and decreasing hydrogen concentration
D. C4H10(g) ↔ C4H6(g) + 2H2(g) -Q 4. Decrease in temperature and increase in hydrogen concentration
9. Establish a correspondence between the equation of a chemical reaction and the shift in chemical equilibrium with increasing pressure in the system.
Reaction equation Direction of chemical equilibrium shift
A. 2HI(g) ↔ H2(g) + I2(s) 1. Shifts towards the direct reaction
B. C(g) + 2S(g) ↔ CS2(g) 2. Shifts towards the reverse reaction
B. C3H6(g) + H2(g) ↔ C3H8(g) 3. There is no shift in equilibrium
G. H2(g) + F2(g) ↔ 2HF(g)
10. Establish a correspondence between the equation of a chemical reaction and a simultaneous change in the conditions for its implementation, leading to a shift in the chemical equilibrium towards a direct reaction.
Reaction equation Changing conditions
A. N2(g) + H2(g) ↔ 2NH3(g) + Q 1. Increase in temperature and pressure
B. N2O4(l) ↔ 2NO2(g) -Q 2. Decrease in temperature and pressure
B. CO2(g) + C(s) ↔ 2CO(g) + Q 3. Increase in temperature and decrease in pressure
D. 4HCl(g) + O2(g) ↔ 2H2O(g) + 2Cl2(g) + Q 4. Decrease in temperature and increase in pressure
Answers: 1 - 3, 2 - 3, 3 - 2, 4 - 4, 5 - 1, 6 - 4, 7 - 4, 8 - 2, 9 - 1, 10 - 1
1. 3223
2. 2111
3. 1322
4. 2221
5. 1211
6. 2312
7. 1211
8. 4133
9. 1113
10. 4322
For the assignments, we thank the collections of exercises for 2016, 2015, 2014, 2013, authors:
Kavernina A.A., Dobrotina D.Yu., Snastina M.G., Savinkina E.V., Zhiveinova O.G.
All chemical reactions are, in principle, reversible.
This means that both the interaction of reagents and the interaction of products occurs in the reaction mixture. In this sense, the distinction between reactants and products is conditional. The direction of a chemical reaction is determined by the conditions of its conduct (temperature, pressure, concentration of substances).
Many reactions have one preferred direction and extreme conditions are required for such reactions to occur in the opposite direction. In such reactions, almost complete conversion of reactants into products occurs.Example. Iron and sulfur, when heated moderately, react with each other to form iron (II) sulfide; FeS is stable under such conditions and practically does not decompose into iron and sulfur:
At 200 atm and 400 0C, the maximum NH3 content in the reaction mixture is reached, equal to 36% (by volume). With a further increase in temperature, due to the increased occurrence of the reverse reaction, the volume fraction of ammonia in the mixture decreases.
Forward and reverse reactions occur simultaneously in opposite directions.
In all reversible reactions, the rate of the forward reaction decreases and the rate of the reverse reaction increases until both rates are equal and equilibrium is established.
In a state of equilibrium, the rates of forward and reverse reactions become equal.
LE CHATELIER'S PRINCIPLE. SHIFT OF CHEMICAL EQUILIBRIUM.
The position of chemical equilibrium depends on the following reaction parameters: temperature, pressure and concentration. The influence that these factors have on a chemical reaction is subject to a pattern that was expressed in general terms in 1884 by the French scientist Le Chatelier. The modern formulation of Le Chatelier's principle is as follows:
1. Effect of temperature. In each reversible reaction, one of the directions corresponds to an exothermic process, and the other to an endothermic process.
2. Effect of pressure. In all reactions involving gaseous substances, accompanied by a change in volume due to a change in the amount of substance during the transition from starting substances to products, the equilibrium position is affected by the pressure in the system.
The influence of pressure on the equilibrium position obeys the following rules:Thus, during the transition from starting substances to products, the volume of gases was halved. This means that with increasing pressure, the equilibrium shifts towards the formation of NH3, as evidenced by the following data for the ammonia synthesis reaction at 400 0C:
3. Effect of concentration. The influence of concentration on the state of equilibrium is subject to the following rules:
