The state of chemical equilibrium depends on a number of factors: temperature, pressure, concentration of reactants. Let us consider in more detail the influence of these factors.

A change in the concentration of the components of an equilibrium system at a constant temperature shifts the equilibrium, however, the value of the equilibrium constant does not change. If the concentration of substance A (or B) is increased for the reaction, then the rate of the forward reaction will increase, and the rate of the reverse reaction will increase. initial moment time will not change. The balance will be broken. Then the concentration of the starting substances will begin to decrease, and the concentration of the reaction products will increase, and this will continue until a new equilibrium is established. In such cases, we say that the equilibrium is shifted towards the formation of reaction products or shifted to the right.

Arguing in the same way, determine for yourself where the equilibrium will shift if the concentration of substance C is increased; decrease the concentration of substance D.

By changing the concentrations of the components, it is possible to shift the equilibrium in the desired direction, increasing or decreasing the yield of reaction products; seeking a more complete use of the starting materials or, conversely,

To complete the second task, we recall that the direct reaction will proceed until one of the components A or B ends. It can be seen from the reaction equation that the reactants react in equimolar * quantities, moreover, their concentrations are equal according to the condition of the problem. Therefore, substances A and B, reacting, will end at the same time. It can also be seen from the reaction equation that when one mole of substance A is converted, two moles of substance C and one mole of substance D are formed. Therefore, some more of them will be added to the amount of substances C and D already in the system. After a simple calculation, we get the desired result:

[A] = [B] = 0 mol/l; [C] = 2 +2 = 4 mol/l; [D] = 2 +1 = 3 mol/l.

Carry out a similar reasoning for the third task, remembering that substances C and D react in a ratio of 2: 1, and the calculation must be carried out according to the amount of the substance that is in short supply (define this substance). Do the calculations and get the result:

[A] \u003d [B] \u003d 1 + 2/2 \u003d 2 mol / l; [C] = 0 mol/l; [D] = 2-2/2 = 1 mol/l.

The equilibrium constant of the reaction A + B C + D is equal to one. Initial concentration [A]o = 0.02 mol/l. How many percent of substance A will undergo transformation if the initial concentrations [B]o are equal to 0.02; 0.1; 0.2?

Denote by x the equilibrium concentration of substance A and write down the expression for the equilibrium constant. The equilibrium concentration of substance B will also be equal to x. The concentrations of the reaction products (C and D) will be equal to each other and equal to 0.02x. (Show this using the reaction equation.)

Let us write an expression for the equilibrium constant.

Kravn. \u003d (0.02 - x) (0.02 - x) / x2 \u003d 1

Having solved the equation for x, we get the result: x \u003d 0.01. Consequently, in the first case, half of substance A (or 50%) underwent transformation.

For the second case, the equilibrium constant will be equal to

Kravn. \u003d (0.02 - x) (0.02 - x) / (0.1 - (0.02 - x)) \u003d 1

Get this expression yourself and, having solved the equation, check the result (x = 0.003). Therefore, (0.02 - 0.003) mol of substance A entered into the reaction, which is 83.5%.

Solve the problem for the third case yourself, and also solve the same problem, denoting the amount of the substance that reacted as x.

An important conclusion can be drawn from the results obtained. To increase the proportion of a substance that reacts at a constant equilibrium constant, it is necessary to increase the amount of the second reagent in the system. A similar problem arises, for example, when recycling waste by chemical means.

With an increase in temperature, the rate of both the forward and reverse reactions will increase, but if the forward reaction is endothermic (?Н > 0), then the rate of the direct reaction will increase more than the rate of the reverse reaction, and the equilibrium will shift towards the formation of products, or to the right. With a negative thermal effect of the forward reaction (exothermic reaction), the rate of the reverse reaction will increase more strongly, and the equilibrium will shift to the left.

Consider for yourself all possible cases of shifting the equilibrium with decreasing temperature.

Figure 5 shows that the difference E "a - E" a is equal to? H of the reaction, which means that the value of the equilibrium constant depends on the magnitude of the thermal effect of the reaction, i.e. whether the reaction is endo or exothermic.

The equilibrium constant of some reaction at 293°K is 5 10-3, and at 1000°K it is 2 10-6. What is the sign of the thermal effect of this reaction?

It follows from the conditions of the problem that as the temperature rises, the equilibrium constant decreases. We use expression (22) and see what the sign of the DH of the reaction should be in order for the constant to decrease.

Kequiv. presented exponential function, the value of which decreases with decreasing argument, in our case, the value of the expression ДH/RT. In order for the value of the argument to decrease, the value of DH must be negative. Therefore, the reaction under consideration is exothermic.

A change in pressure noticeably affects the state of systems that include gaseous components. In this case, in accordance with gas laws there is a change in the volume of the system, and this leads to a change in the concentration of gaseous substances (or their partial pressures). So, with increasing pressure, the volume will decrease, and the concentration of gaseous substances will increase. An increase in concentration leads, as we already know, to a shift in equilibrium towards the consumption of a reagent that has increased its concentration. In this case, it can be formulated somewhat differently. ?When pressure increases, the equilibrium shifts towards a smaller amount of gaseous substances, or, more simply, towards a decrease in the number of molecules of gaseous substances. The concentration of solids and liquids does not change with pressure.

Consider the classic example of the synthesis of ammonia from nitrogen and hydrogen

3H2 + N2 - 2NH3, (DN< 0).

Since the system consists only of gaseous substances, and when ammonia is formed, the number of molecules decreases, then with increasing pressure, the equilibrium will shift to the right, towards a greater output of ammonia. Therefore, the industrial synthesis of ammonia is carried out at elevated pressure.

Suggest yourself temperature conditions ammonia synthesis, knowing the thermal effect of the reaction and subject to the maximum yield of the product. How do these conditions correlate with the kinetic factors of the process?

How will the pressure increase affect the equilibrium of the following reactions?

chemical kinetics catalyst inhibitor

CaCO3 (c.) - CaO (c.) + CO2 (g.);

4Fe(c.) + 3O2(g.) - 2Fe2O3(c.).

In the first reaction, only carbon dioxide CO2 is gaseous, therefore, with increasing pressure, the equilibrium will shift to the left, towards a decrease in the amount of gaseous substance.

Consider the second case yourself.

How should the pressure in these reactions be changed in order to achieve a higher yield of products?

All cases of a change in the state of an equilibrium system under external influences can be generalized by formulating the Le Chatelier principle:

If a system in equilibrium is subjected to external influence, then the equilibrium shifts in the direction that weakens the effect of external influence.

Check whether Le Chatelier's principle is satisfied in all cases considered above.

Give your own examples of equilibrium shifts when external conditions change and explain them on the basis of Le Chatelier's principle.

So, we have considered the main issues related to the laws of the course of chemical reactions. Knowledge of these patterns will make it possible to meaningfully influence the conditions for carrying out certain processes in order to obtain the optimal result.

Questions for self-control

• 1. What reactions are called reversible?
• 2. How and why do the rates of forward and reverse reactions change over time?
• 3. What is called chemical equilibrium?
• 4. What value quantitatively characterizes the chemical equilibrium?
• 5. What determines the value of the equilibrium constant: the concentration of reacting substances; the nature of the reactants; total pressure; temperature; the presence of a catalyst?
• 6. What are the characteristics of true chemical equilibrium?
• 7. What is the difference between false chemical equilibrium and true equilibrium?
• 8. Give the formulation of Le Chatelier's principle.
• 9. Formulate the consequences of Le Chatelier's principle.

The study of the parameters of the system, including the initial substances and reaction products, allows us to find out what factors shift the chemical equilibrium and lead to the desired changes. Based on the conclusions of Le Chatelier, Brown and other scientists about the methods of carrying out reversible reactions, industrial technologies are based that make it possible to carry out processes that previously seemed impossible and obtain economic benefits.

Variety of chemical processes

According to the characteristics of the thermal effect, many reactions are classified as exothermic or endothermic. The former go with the formation of heat, for example, the oxidation of carbon, the hydration of concentrated sulfuric acid. The second type of changes is associated with the absorption of thermal energy. Examples of endothermic reactions: the decomposition of calcium carbonate with the formation of slaked lime and carbon dioxide, the 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 reactants 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. The formation of end products from reactants is a direct reaction. In the reverse, the initial substances are obtained from the products of their decomposition or synthesis. In the reacting mixture, a chemical equilibrium arises, in which as many compounds are obtained as the initial molecules decompose. In reversible processes, instead of the "=" sign between the reactants and products, the symbols "↔" or "⇌" are used. Arrows can be unequal in length, which is associated with the dominance of one of the reactions. In chemical equations, aggregate characteristics of substances can be indicated (g - gases, w - liquids, m - solids). Scientifically substantiated methods of influencing reversible processes are of great practical importance. Thus, the production of ammonia became profitable after the creation of conditions that shift 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, the formation of a gas that leaves the reaction sphere. These processes include ion exchange, decomposition of substances.

Chemical equilibrium and conditions for its displacement

Several factors influence the characteristics of the forward and reverse processes. One of them is time. The concentration of the substance taken for the reaction gradually decreases, and the final compound increases. The reaction of the forward direction is slower and slower, the reverse process is gaining speed. In a certain interval, two opposite processes go synchronously. The interaction between substances occurs, but the concentrations do not change. The reason is the dynamic chemical equilibrium established in the system. Its retention or modification depends on:

• temperature conditions;
• compound concentrations;
• pressure (for gases).

Shift in chemical equilibrium

In 1884, A. L. Le Chatelier, an outstanding scientist from France, proposed a description of ways to bring a system out of a state of dynamic equilibrium. The method is based on the principle of leveling the action of external factors. Le Chatelier drew attention to the fact that processes arise in the reacting mixture that compensate for the influence of extraneous forces. The principle formulated by a French researcher states that a change in conditions in a state of equilibrium favors the course of a reaction that weakens an extraneous influence. Equilibrium shift obeys this rule, it is observed when the composition, temperature conditions and pressure change. 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.

Influence of concentration

A shift in equilibrium occurs if certain components are removed from the interaction zone or additional portions of a substance are introduced. The removal of products from the reaction mixture usually causes an increase in the rate of their formation, while the addition of substances, on the contrary, leads to their predominant 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 COOSH 3 + H 2 O. If you add oxygen that interacts with sulfur dioxide, then the chemical equilibrium shifts towards the direct reaction of the formation of sulfur trioxide. Oxygen binds to SO 3 molecules, its concentration decreases, which is consistent with Le Chatelier's rule for reversible processes.

Temperature change

Processes that go with the absorption or release of heat are endo- 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 release heat. During the interaction of carbon dioxide 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).

Pressure influence

The change in pressure is an important factor for reacting mixtures that include gaseous compounds. You should also pay attention to the difference in the volumes of the initial and resulting substances. A decrease in pressure leads to a predominant occurrence of phenomena in which the total volume of all components increases. The increase in pressure directs the process in the direction of reducing the volume of the entire system. This pattern is observed in the reaction of ammonia formation: 0.5N 2 (g) + 1.5H 2 (g) ⇌ NH 3 (g). A change in pressure will not affect the chemical equilibrium in those reactions that take place at a constant volume.

Optimal conditions for the implementation of the chemical process

The creation of conditions for shifting the equilibrium largely determines the development of modern chemical technologies. The practical use of scientific theory contributes to obtaining optimal production results. The most striking example is the production of ammonia: 0.5N 2 (g) + 1.5H 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 a complex substance 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 volume of the target product. An increase in pressure will provide an increase in the yield of NH 3 .

Under production conditions, the optimal ratio of all parameters (temperature, concentration, pressure) is selected. In addition, it has great importance area of ​​contact between the reactants. 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.

Task

Specify how it will affect:

a) increase in pressure;

b) temperature increase;

c) increase in oxygen concentration to balance the system:

2CO(G) + O 2 (G) ↔ 2CO 2 (G) + Q

Solution:

a) A change in pressure shifts the equilibrium of reactions involving gaseous substances (d). Let us determine the volumes of gaseous substances before and after the reaction by stoichiometric coefficients:

According to Le Chatelier's principle, with increasing pressure , the balance is shifting towards educationi substances occupying less about b b eat, therefore, the equilibrium will shift to the right, i.e. towards the formation of CO 2, towards the direct reaction (→) .

b) According to Le Chatelier's principle, when the temperature rises, the balance shifts towards an endothermic reaction (- Q ), i.e. in the direction of the reverse reaction - the decomposition reaction of CO 2 (←) , because law of conservation of energy:

Q - 2 CO (g) + O 2 (g) ↔ 2 CO 2 (g) + Q

V) As the oxygen concentration increases the equilibrium of the system is shifting towards obtaining CO 2 (→) becausean increase in the concentration of reactants (liquid or gaseous) shifts towards products, i.e. towards a direct reaction.

Additionally:

Example 1 How many times will the rate of forward and reverse reactions change in the system:

2 SO 2 (d) +O 2 (d) = 2SO 3 (G)

if the volume of the gas mixture is tripled? In which direction will the equilibrium of the system shift?

Solution. Let us denote the concentrations of reacting substances: [SO 2 ]= a , [ABOUT 2 ] = b , [ SO 3 ] = With. According to the law of action of masses of speedv forward and reverse reactions before volume change:

v etc = Ka 2 b

v arr = TO 1 With 2 .

After reducing the volume of a homogeneous system by a factor of three, the concentration of each of the reactants will increase by a factor of three: [SO 2 ] = 3 A , [ABOUT 2 ] = 3 b ; [ SO 3 ] = 3 With . At new speed concentrationsv ’ forward and backward reaction:

v ’ etc = TO (3 A ) 2 (3 b ) = 27 Ka 2 b

v ’ arr = TO 1 (3 With ) 2 = 9 TO 1 With 2

From here:

Consequently, the rate of the forward reaction increased by 27 times, and the reverse - only nine times. The equilibrium of the system has shifted towards educationSO 3 .

Example 2 Calculate how many times the rate of a reaction proceeding in the gas phase will increase with an increase in temperature from 30 to 70 O C if the temperature coefficient of the reaction is 2.

Solution. The dependence of the rate of a chemical reaction on temperature is determined by the Van't Hoff empirical rule according to the formula:

Therefore, the reaction rateν T 2 at a temperature of 70 O With more reaction speedν T 1 at a temperature of 30 O C 16 times.

Example 3 Equilibrium constant of a homogeneous system:

CO(g) + H 2 O(g) = CO 2 (d) + H 2 (G)

at 850 O C is equal to 1. Calculate the concentrations of all substances at equilibrium if the initial concentrations are: [CO] ref \u003d 3 mol / l, [N 2 ABOUT] ref = 2 mol/l.

Solution. At equilibrium, the rates of the forward and reverse reactions are equal, and the ratio of the constants of these rates is constant and is called the equilibrium constant of the given system:

v pr = TO 1 [DREAM 2 ABOUT]

v arr = K 2 [CO 2 ][N 2 ]

In the condition of the problem, the initial concentrations are given, while in the expressionTO R includes only the equilibrium concentrations of all substances in the system. Let us assume that by the moment of equilibrium of the concentration [СО 2 ] R = X mol/l. According to the equation of the system, the number of moles of hydrogen formed in this case will also beX mol/l. For the same number of moles (X mol/l) CO and H 2 O spent for educationX moles of CO 2 and H 2 . Therefore, the equilibrium concentrations of all four substances are:

[CO 2 ] R = [N 2 ] R = X mol/l;

[CO] R = (3 – X ) mol/l;

[N 2 ABOUT] R = (2 – X ) mol/l.

Knowing the equilibrium constant, we find the valueX , and then the initial concentrations of all substances:

Thus, the desired equilibrium concentrations are:

[CO 2 ] R = 1.2 mol/l;

[N 2 ] R = 1.2 mol/l;

[CO] R \u003d 3 - 1.2 \u003d 1.8 mol / l;

[N 2 ABOUT] R \u003d 2 - 1.2 \u003d 0.8 mol / l.

Example 4 At a certain temperature, the equilibrium concentrations in the system

2CO (g) + O 2 (g) ↔ 2CO 2 (g) were: = 0.2 mol/l, = 0.32 mol/l, = 0.16 mol/l. Determine the equilibrium constant at this temperature and the initial concentrations of CO and O 2 if the initial mixture did not contain CO 2 .

Solution:

1). Since equilibrium concentrations are given in the condition of the problem, the equilibrium constant is 2:

2). If the initial mixture did not contain CO 2, then at the moment of chemical equilibrium, 0.16 mol of CO 2 was formed in the system.

According to UHR:

2CO (g) + O 2 (g) ↔ 2CO 2 (g)

The formation of 0.16 mol CO 2 spent:

υ reacted (CO) \u003d υ (CO 2) \u003d 0.16 mol

υ reacted (O 2) \u003d 1/2υ (CO 2) \u003d 0.08 mol

Hence,

υ initial = υ reacted + υ equilibrium

υ initial (CO) \u003d 0.16 + 0.2 \u003d 0.36 mol

υ initial (O 2) \u003d 0.08 + 0.32 \u003d 0.4 mol

Substance			CO2
C initial	0,36
C reacted	0,16	0,08	0,16
C equilibrium		0,32	0,16

Example 5Determine the equilibrium concentration of HI in the system

H 2 (g) + I 2 (g) ↔ 2HI (g),

if at some temperature the equilibrium constant is 4, and the initial concentrations of H 2 , I 2 and HI are 1, 2 and 0 mol/l, respectively.

Solution. Let x mol/l HI

Substance	H2	I 2
from the original , mol/l
with proreact. , mol/l	x/2	x/2
c equal. , mol/l	1x/2	PCl 5 (d) = RS l 3 (d) + WITH l 2(G); Δ H= + 92.59 kJ. How to change: a) temperature; b) pressure; c) concentration in order to shift the equilibrium towards a direct reaction - decompositionPCl 5 ? Solution. A shift or shift in chemical equilibrium is a change in the equilibrium concentrations of reactants as a result of a change in one of the reaction conditions. The direction in which the equilibrium has shifted is determined according to Le Chatelier's principle: a) since the decomposition reactionPCl 5 endothermic (Δ H > 0) then to shift the equilibrium towards a direct reaction, it is necessary to increase the temperature; b) since in this system the expansion of PCl 5 leads to an increase in volume (two gaseous molecules are formed from one gas molecule), then to shift the equilibrium towards a direct reaction, it is necessary to reduce the pressure; c) shifting the equilibrium in the indicated direction can be achieved as an increase in the concentration of RSl 5 , and a decrease in the concentration of PCl 3 or Cl 2 .

Chemical reactions are reversible and irreversible.

irreversible reactions called such reactions that go in only one (forward →) direction:

those. if some reaction A + B = C + D is irreversible, this means that the reverse reaction C + D = A + B does not occur.

Reversible reactions - these are reactions that go both in the forward and in the opposite direction (⇄):

i.e., for example, if a certain reaction A + B = C + D is reversible, this means that both the reaction A + B → C + D (direct) and the reaction C + D → A + B (reverse) proceed simultaneously ).

In fact, because both direct and reverse reactions proceed, reagents (starting substances) in the case of reversible reactions can be called both substances on the left side of the equation and substances on the right side of the equation. The same goes for products.

For any reversible reaction, it is possible that the rates of the forward and reverse reactions are equal. Such a state is called state of equilibrium.

In a state of equilibrium, the concentrations of both all reactants and all products are unchanged. The concentrations of products and reactants at equilibrium are called equilibrium concentrations.

Shift in chemical equilibrium under the influence of various factors

Due to such external influences on the system as a change in temperature, pressure or concentration of starting substances or products, the equilibrium of the system may be disturbed. However, after the cessation of this external influence, the system will pass to a new state of equilibrium after some time. Such a transition of a system from one equilibrium state to another equilibrium state is called shift (shift) of chemical equilibrium .

In order to be able to determine how the chemical equilibrium shifts with a particular type of exposure, it is convenient to use the Le Chatelier principle:

If any external influence is exerted on a system in a state of equilibrium, then the direction of the shift in chemical equilibrium will coincide with the direction of the reaction that weakens the effect of the impact.

The influence of temperature on the state of equilibrium

When the temperature changes, the equilibrium of any chemical reaction shifts. This is due to the fact that any reaction has a thermal effect. In this case, the thermal effects of the forward and reverse reactions are always directly opposite. Those. if the forward reaction is exothermic and proceeds with a thermal effect equal to +Q, then the reverse reaction is always endothermic and has a thermal effect equal to -Q.

Thus, in accordance with Le Chatelier's principle, if we increase the temperature of some system that is in a state of equilibrium, then the equilibrium will shift towards the reaction, during which the temperature decreases, i.e. towards an endothermic reaction. And similarly, if we lower the temperature of the system in a state of equilibrium, the equilibrium will shift towards the reaction, as a result of which the temperature will increase, i.e. towards an exothermic reaction.

For example, consider the following reversible reaction and indicate where its equilibrium will shift as the temperature decreases:

As you can see from the equation above, the forward reaction is exothermic, i.e. as a result of its flow, heat is released. Therefore, the reverse reaction will be endothermic, that is, it proceeds with the absorption of heat. According to the condition, the temperature is lowered, therefore, the equilibrium will shift to the right, i.e. towards a direct reaction.

Effect of concentration on chemical equilibrium

An increase in the concentration of reagents in accordance with the Le Chatelier principle should lead to a shift in equilibrium towards the reaction in which the reagents are consumed, i.e. towards a direct reaction.

Conversely, if the concentration of the reactants is lowered, then the equilibrium will shift towards the reaction that results in the formation of the reactants, i.e. side of the reverse reaction (←).

A change in the concentration of reaction products also affects in a similar way. If you increase the concentration of products, the equilibrium will shift towards the reaction, as a result of which the products are consumed, i.e. towards the reverse reaction (←). If, on the contrary, the concentration of products is lowered, then the equilibrium will shift towards the direct reaction (→), in order for the concentration of products to increase.

Effect of pressure on chemical equilibrium

Unlike temperature and concentration, a change in pressure does not affect the equilibrium state of every reaction. In order for a change in pressure to lead to a shift in chemical equilibrium, the sums of the coefficients in front of gaseous substances on the left and right sides of the equation must be different.

Those. from two reactions:

a change in pressure can affect the state of equilibrium only in the case of the second reaction. Since the sum of the coefficients in front of the formulas of gaseous substances in the case of the first equation on the left and right is the same (equal to 2), and in the case of the second equation it is different (4 on the left and 2 on the right).

From this, in particular, it follows that if there are no gaseous substances among both the reactants and the products, then a change in pressure will not affect the current state of equilibrium in any way. For example, pressure will not affect the equilibrium state of the reaction:

If the amount of gaseous substances is different on the left and on the right, then an increase in pressure will lead to a shift in equilibrium towards the reaction, during which the volume of gases decreases, and a decrease in pressure in the direction of the reaction, as a result of which the volume of gases increases.

Effect of a catalyst on chemical equilibrium

Since a catalyst equally accelerates both the forward and reverse reactions, its presence or absence does not affect to a state of equilibrium.

The only thing that a catalyst can affect is the rate of transition of the system from a non-equilibrium state to an equilibrium one.

The impact of all the above factors on chemical equilibrium is summarized below in a cheat sheet, which at first you can peek at when performing balance tasks. However, she will not be able to use it in the exam, therefore, after analyzing several examples with her help, she should be taught and trained to solve tasks for balance, no longer peeping into her:

Designations: T - temperature, p - pressure, With – concentration, – increase, ↓ – decrease

Catalyst

T	T - equilibrium shifts towards an endothermic reaction
	↓T - the equilibrium shifts towards an exothermic reaction
p	p - the equilibrium shifts towards the reaction with a smaller sum of coefficients in front of gaseous substances
	↓p - the equilibrium shifts towards the reaction with a larger sum of coefficients in front of gaseous substances
c	c (reagent) - the equilibrium shifts towards the direct reaction (to the right)
	↓c (reagent) - the equilibrium shifts towards the reverse reaction (to the left)
	c (product) - the equilibrium shifts in the direction of the reverse reaction (to the left)
	↓c (product) - the equilibrium shifts towards the direct reaction (to the right)
Doesn't affect balance!

In accordance with Le Chatelier's principle If an external influence is exerted on a system that is in a state of equilibrium, then the equilibrium will shift in the direction of the reaction that weakens this influence.

For example

3H 2 + N 2 2NH 3 - DH.

1. Effect of concentration. If the concentration of the starting substances is increased, then the equilibrium will shift towards the formation of products and vice versa.

If the concentrations of N 2 and H 2 starting substances are reduced, this will lead to a shift in equilibrium from right to left, as a result of which the concentrations of N 2 and H 2 will again increase due to the decomposition of ammonia.

2. Influence of pressure. In this case, only gaseous participants in the reaction are taken into account. With increasing pressure, the equilibrium shifts towards a system consisting of a smaller number of moles of gaseous substances.

An increase in system pressure will lead to a shift in equilibrium from left to right, since on the left side total number mole of gases 4, and in the right 2.

3. Influence of temperature. Depends on the thermal effect of the reaction.

Chemical equations in which the heat effect of reactions is indicated are called thermochemical equations. In the thermochemical equations of chemical reactions, the thermal effect is indicated using the quantity DH, which is called enthalpy change(heat content) of the reaction. Enthalpy is a measure of the energy accumulated by a substance during its formation.

–DH, heat is released, i.e. the reaction is exothermic;

DH, heat is absorbed, i.e. the reaction is endothermic;

The direct reaction is exothermic, i.e. as the temperature rises, the equilibrium will shift from right to left, towards an endothermic reaction.

4. Influence of the catalyst. Catalysts equally accelerate both the forward and reverse reactions, and therefore do not shift the chemical equilibrium, but only contribute to a more rapid achievement of the equilibrium state.

Exercise. Gas system A + B C - DH. What effect will the equilibrium concentration of substance C have on:

a) increase in pressure. On the left side there are 2 moles of substances. In the right 1 mol, i.e. the equilibrium shifts from left to right towards the formation of substance C, the concentration of C increases. (®)

b) an increase in the concentration of substance A. The equilibrium shifts from left to right towards the formation of substance C, the concentration C increases. (®).

c) an increase in temperature. Direct exo, reverse - endothermic. The balance will shift from right to left ().

Exercise. How will the pressure increase affect the equilibrium of the system?

Fe 3 O 4 (tv) + CO (g) 3FeO + CO 2 (g)

The equilibrium in the system will not shift.

Exercise. How should the temperature, pressure and concentration be changed in order to shift the equilibrium in the direction of the direct reaction?

PCl 5(g) PCl 3(g) + Cl 2(g) + 92.59 kJ

a) the reaction is endothermic, the temperature must be increased.

b) the pressure must be reduced

c) either increase the concentration of PCl 5 or decrease the concentration of PCl 3 and Cl 2 .

Exercise. 2SO 2 (g) + O 2 (g) Û 2SO 3 (g). What effect will the equilibrium state have?

a) increase in pressure;

When the direct reaction proceeds, the amount of gaseous substances in the system decreases (from 2 mol of SO 2 gas and 1 mol of O 2 gas, liquid SO 3 is formed). An increase in pressure will shift the equilibrium towards the formation of a smaller amount of gaseous substances, i.e. SO 3. (®).

b) decrease in the concentration of sulfur oxide (VI)?

A decrease in SO 3 concentration (removal of the product from the reaction system) will cause a shift in the equilibrium towards the formation of SO 3 . (®).

Exercise. A + B Û 2C -

What effect will they have on the equilibrium state.