Where will the equilibrium shift as concentration increases? Effect of temperature on chemical equilibrium

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 a pattern that was expressed in general terms 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 toward a smaller volume of substances, and as pressure decreases toward 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 turned into the target reaction product, for example, what part of SO 2 turned 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.)

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 the 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 original amount of the reagent, i.e. , and the calculation formula. In accordance with the second definition, the amount of the reagent actually converted 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 yield is no longer equal to the degree of conversion. 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.

9. Rate of chemical reaction. Chemical equilibrium

9.2. Chemical equilibrium and its displacement

Most chemical reactions are reversible, i.e. simultaneously flow both in the direction of the formation of products and in the direction of their decomposition (from left to right and from right to left).

Examples of reaction equations for reversible processes:

N 2 + 3H 2 ⇄ t °, p, cat 2NH 3

2SO 2 + O 2 ⇄ t ° , p , cat 2SO 3

H 2 + I 2 ⇄ t ° 2HI

Reversible reactions are characterized by a special state called a state of chemical equilibrium.

Chemical equilibrium- this is a state of the system in which the rates of forward and reverse reactions become equal. When moving towards chemical equilibrium, the rate of the forward reaction and the concentration of reactants decrease, while the reverse reaction and the concentration of products increase.

In a state of chemical equilibrium, as much product is formed per unit time as it is decomposed. As a result, the concentrations of substances in a state of chemical equilibrium do not change over time. However, this does not mean at all that the equilibrium concentrations or masses (volumes) of all substances are necessarily equal to each other (see Fig. 9.8 and 9.9). Chemical equilibrium is a dynamic (mobile) equilibrium that can respond to external influences.

The transition of an equilibrium system from one equilibrium state to another is called a displacement or shift in equilibrium. In practice, they talk about a shift in equilibrium towards the reaction products (to the right) or towards the starting substances (to the left); a forward reaction is one that occurs from left to right, and a reverse reaction occurs from right to left. The state of equilibrium is shown by two oppositely directed arrows: ⇄.

The principle of shifting equilibrium was formulated by the French scientist Le Chatelier (1884): an external influence on a system that is in equilibrium leads to a shift in this equilibrium in a direction that weakens the effect of the external influence

Let us formulate the basic rules for shifting equilibrium.

Effect of concentration: when the concentration of a substance increases, the equilibrium shifts towards its consumption, and when it decreases, towards its formation.

For example, with an increase in the concentration of H 2 in a reversible reaction

H 2 (g) + I 2 (g) ⇄ 2HI (g)

the rate of the forward reaction, depending on the hydrogen concentration, will increase. As a result, the balance will shift to the right. As the concentration of H 2 decreases, the rate of the forward reaction will decrease, as a result, the equilibrium of the process will shift to the left.

Effect of temperature: When the temperature increases, the equilibrium shifts towards the endothermic reaction, and when the temperature decreases, it shifts towards the exothermic reaction.

It is important to remember that with increasing temperature, the rate of both exo- and endothermic reactions increases, but the endothermic reaction increases more times, for which E a is always greater. As the temperature decreases, the rate of both reactions decreases, but again by a greater number of times - endothermic. It is convenient to illustrate this with a diagram in which the speed value is proportional to the length of the arrows, and the equilibrium shifts in the direction of the longer arrow.

Effect of pressure: A change in pressure affects the state of equilibrium only when gases are involved in the reaction, and even when the gaseous substance is on only one side of the chemical equation. Examples of reaction equations:

• pressure affects the equilibrium shift:

3H 2 (g) + N 2 (g) ⇄ 2NH 3 (g),

CaO (tv) + CO 2 (g) ⇄ CaCO 3 (tv);

• pressure does not affect the equilibrium shift:

Cu (sv) + S (sv) = CuS (sv),

NaOH (solution) + HCl (solution) = NaCl (solution) + H 2 O (l).

When the pressure decreases, the equilibrium shifts towards the formation of a larger chemical amount of gaseous substances, and when it increases, the equilibrium shifts towards the formation of a smaller chemical amount of gaseous substances. If the chemical quantities of gases in both sides of the equation are the same, then pressure does not affect the state of chemical equilibrium:

H 2 (g) + Cl 2 (g) = 2HCl (g).

This is easy to understand, given that the effect of a change in pressure is similar to the effect of a change in concentration: when the pressure increases n times, the concentration of all substances in equilibrium increases by the same amount (and vice versa).

Effect of the volume of the reaction system: a change in the volume of the reaction system is associated with a change in pressure and affects only the equilibrium state of reactions involving gaseous substances. A decrease in volume means an increase in pressure and shifts the equilibrium toward the formation of fewer chemical gases. An increase in the volume of the system leads to a decrease in pressure and a shift in equilibrium towards the formation of a larger chemical amount of gaseous substances.

The introduction of a catalyst into an equilibrium system or a change in its nature does not shift the equilibrium (does not increase the yield of the product), since the catalyst accelerates both forward and reverse reactions to the same extent. This is due to the fact that the catalyst equally reduces the activation energy of the forward and reverse processes. Then why do they use a catalyst in reversible processes? The fact is that the use of a catalyst in reversible processes promotes the rapid onset of equilibrium, and this increases the efficiency of industrial production.

Specific examples of the influence of various factors on the equilibrium shift are given in Table. 9.1 for the ammonia synthesis reaction that occurs with the release of heat. In other words, the forward reaction is exothermic, and the reverse reaction is endothermic.

Table 9.1

The influence of various factors on the shift in the equilibrium of the ammonia synthesis reaction

Example 9.3. In a state of process equilibrium

2SO 2 (g) + O 2 (g) ⇄ 2SO 3 (g)

the concentrations of substances (mol/dm 3) SO 2, O 2 and SO 3 are respectively 0.6, 0.4 and 0.2. Find the initial concentrations of SO 2 and O 2 (the initial concentration of SO 3 is zero).

Solution. During the reaction, SO 2 and O 2 are consumed, therefore

c out (SO 2) = c equal (SO 2) + c out (SO 2),

c out (O 2) = c equal (O 2) + c out (O 2).

The value of c expended is found using c (SO 3):

x = 0.2 mol/dm3.

c out (SO 2) = 0.6 + 0.2 = 0.8 (mol/dm 3).

y = 0.1 mol/dm3.

c out (O 2) = 0.4 + 0.1 = 0.5 (mol/dm 3).

Answer: 0.8 mol/dm 3 SO 2; 0.5 mol/dm 3 O 2.

When performing exam tasks, the influence of various factors, on the one hand, on the reaction rate, and on the other, on the shift in chemical equilibrium, is often confused.

For a reversible process

with increasing temperature, the rate of both forward and reverse reactions increases; as the temperature decreases, the rate of both forward and reverse reactions decreases;

with increasing pressure, the rates of all reactions occurring with the participation of gases increase, both direct and reverse. As the pressure decreases, the rate of all reactions occurring with the participation of gases, both direct and reverse, decreases;

introducing a catalyst into the system or replacing it with another catalyst does not shift the equilibrium.

Example 9.4. A reversible process occurs, described by the equation

N 2 (g) + 3H 2 (g) ⇄ 2NH 3 (g) + Q

Consider which factors: 1) increase the rate of synthesis of the ammonia reaction; 2) shift the balance to the right:

a) decrease in temperature;

b) increase in pressure;

c) decrease in NH 3 concentration;

d) use of a catalyst;

e) increase in N 2 concentration.

Solution. Factors b), d) and e) increase the reaction rate of ammonia synthesis (as well as increasing temperature, increasing H 2 concentration); shift the balance to the right - a), b), c), e).

Answer: 1) b, d, d; 2) a, b, c, d.

Example 9.5. Below is the energy diagram of a reversible reaction

List all true statements:

a) the reverse reaction proceeds faster than the forward reaction;

b) with increasing temperature, the rate of the reverse reaction increases more times than the direct reaction;

c) a direct reaction occurs with the absorption of heat;

d) the temperature coefficient γ is greater for the reverse reaction.

Solution.

a) The statement is correct, since E arr = 500 − 300 = 200 (kJ) is less than E arr = 500 − 200 = 300 (kJ).

b) The statement is incorrect; the rate of the direct reaction for which E a is greater increases by a greater number of times.

c) The statement is correct, Q pr = 200 − 300 = −100 (kJ).

d) The statement is incorrect, γ is greater for a direct reaction, in which case E a is greater.

Answer: a), c).

Chemical reactions can be reversible or irreversible.

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

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) occur simultaneously ).

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

For any reversible reaction, a situation is possible when the rates of the forward and reverse reactions are equal. This condition is called state of balance.

At equilibrium, the concentrations of both all reactants and all products are constant. The concentrations of products and reactants at equilibrium are called equilibrium concentrations.

Shift in chemical equilibrium under the influence of various factors

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

In order to be able to determine how the chemical equilibrium shifts under a particular type of influence, it is convenient to use Le Chatelier’s 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 influence.

The influence of temperature on the state of equilibrium

When temperature changes, the equilibrium of any chemical reaction shifts. This is due to the fact that any reaction has a thermal effect. Moreover, 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 can be seen from the equation above, the forward reaction is exothermic, i.e. As a result of its occurrence, heat is released. Consequently, the reverse reaction will be endothermic, that is, it occurs with the absorption of heat. According to the condition, the temperature is reduced, therefore, the equilibrium will shift to the right, i.e. towards direct reaction.

Effect of concentration on chemical equilibrium

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

And vice versa, if the concentration of the reactants is reduced, then the equilibrium will shift towards the reaction as a result of which the reactants are formed, i.e. side of the reverse reaction (←).

A change in the concentration of reaction products also has a similar effect. If the concentration of products is increased, 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 reduced, then the equilibrium will shift towards the direct reaction (→), so that the concentration of products increases.

Effect of pressure on chemical equilibrium

Unlike temperature and concentration, changes in pressure do 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 for gaseous substances on the left and right sides of the equation must be different.

Those. of two reactions:

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

If, on the left and right, the amount of gaseous substances differs, 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 will lead to a shift in the equilibrium, as a result of which the volume of gases increases.

Effect of a catalyst on chemical equilibrium

Since a catalyst equally accelerates both forward and reverse reactions, its presence or absence has no effect to a state of equilibrium.

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

The impact of all the above factors on chemical equilibrium is summarized below in a cheat sheet, which you can initially look at when performing equilibrium tasks. However, it will not be possible to use it in the exam, so after analyzing several examples with its help, you should learn it and practice solving equilibrium problems without looking at it:

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

1. Among all known reactions, a distinction is made between reversible and irreversible reactions. When studying ion exchange reactions, the conditions under which they proceed to completion were listed. ().

There are also known reactions that, under given conditions, do not proceed to completion. So, for example, when sulfur dioxide is dissolved in water, the reaction occurs: SO 2 + H 2 O→ H2SO3. But it turns out that only a certain amount of sulfurous acid can form in an aqueous solution. This is explained by the fact that sulfurous acid is fragile, and a reverse reaction occurs, i.e. decomposition into sulfur oxide and water. Consequently, this reaction does not go to completion because two reactions occur simultaneously - straight(between sulfur oxide and water) and reverse(decomposition of sulfurous acid). SO 2 +H 2 O↔ H 2 SO 3 .

Chemical reactions occurring under given conditions in mutually opposite directions are called reversible.

2. Since the rate of chemical reactions depends on the concentration of the reactants, at first the rate of the direct reaction( υ pr) should be maximum, and the speed of the reverse reaction ( υ arr.) is equal to zero. The concentration of reactants decreases over time, and the concentration of reaction products increases. Therefore, the rate of the forward reaction decreases and the rate of the reverse reaction increases. At a certain point in time, the rates of forward and reverse reactions become equal:

In all reversible reactions, the rate of the forward reaction decreases, the rate of the reverse reaction increases until both rates become equal and an equilibrium state is established:

υ pr =υ arr.

The state of the system in which the rate of the forward reaction is equal to the rate of the reverse reaction is called chemical equilibrium.

In a state of chemical equilibrium, the quantitative ratio between the reactants and reaction products remains constant: how many molecules of the reaction product are formed per unit time, so many of them decompose. However, the state of chemical equilibrium is maintained as long as the reaction conditions remain unchanged: concentration, temperature and pressure.

The state of chemical equilibrium is described quantitatively law of mass action.

At equilibrium, the ratio of the product of concentrations of reaction products (in powers of their coefficients) to the product of concentrations of reactants (also in powers of their coefficients) is a constant value, independent of the initial concentrations of substances in the reaction mixture.

This constant is called equilibrium constant - k

So for the reaction: N 2 (G) + 3 H 2 (G) ↔ 2 NH 3 (G) + 92.4 kJ the equilibrium constant is expressed as follows:

υ 1 =υ 2

v 1 (direct reaction) = k 1 [ N 2 ][ H 2 ] 3 , where– equilibrium molar concentrations, = mol/l

υ 2 (backlash) = k 2 [ N.H. 3 ] 2

k 1 [ N 2 ][ H 2 ] 3 = k 2 [ N.H. 3 ] 2

K p = k 1 / k 2 = [ N.H. 3 ] 2 / [ N 2 ][ H 2 ] 3 – equilibrium constant.

Chemical equilibrium depends on concentration, pressure, temperature.

Principledetermines the direction of equilibrium mixing:

If an external influence is exerted on a system that is in equilibrium, then the equilibrium in the system will shift in the direction opposite to this influence.

1) Effect of concentration – if the concentration of the starting substances is increased, the equilibrium shifts towards the formation of reaction products.

For example,K p = k 1 / k 2 = [ N.H. 3 ] 2 / [ N 2 ][ H 2 ] 3

When added to the reaction mixture, for example nitrogen, i.e. the concentration of the reagent increases, the denominator in the expression for K increases, but since K is a constant, then to fulfill this condition the numerator must also increase. Thus, the amount of reaction product in the reaction mixture increases. In this case, they speak of a shift in chemical equilibrium to the right, towards the product.

Thus, an increase in the concentration of reactants (liquid or gaseous) shifts towards the products, i.e. towards direct reaction. An increase in the concentration of products (liquid or gaseous) shifts the equilibrium towards the reactants, i.e. towards the opposite reaction.

Changing the mass of a solid does not change the equilibrium position.

2) Effect of temperature – an increase in temperature shifts the equilibrium towards an endothermic reaction.

A)N 2 (G) + 3H 2 (D) ↔ 2N.H. 3 (G) + 92.4 kJ (exothermic - heat release)

As the temperature increases, the equilibrium will shift towards the ammonia decomposition reaction (←)

b)N 2 (G) +O 2 (D) ↔ 2NO(G) – 180.8 kJ (endothermic - heat absorption)

As the temperature increases, the equilibrium will shift towards the formation reaction NO (→)

3) Influence of pressure (only for gaseous substances) – with increasing pressure, the equilibrium shifts towards the formationI substances occupying less o I eat.

N 2 (G) + 3H 2 (D) ↔ 2N.H. 3 (G)

1 V - N 2

3 V - H 2

2 V – N.H. 3

With increasing pressure ( P): before reaction4 V gaseous substances → after the reaction2 Vgaseous substances, therefore, the equilibrium shifts to the right ( → )

When the pressure increases, for example, by 2 times, the volume of gases decreases by the same amount, and therefore, the concentrations of all gaseous substances will increase by 2 times. K p = k 1 / k 2 = [ N.H. 3 ] 2 / [ N 2 ][ H 2 ] 3

In this case, the numerator of the expression for K will increase by 4 times, and the denominator is 16 times, i.e. equality will be violated. To restore it, the concentration must increase ammoniaand concentrations decrease nitrogenAndwaterkind. The balance will shift to the right.

So, when the pressure increases, the equilibrium shifts towards a decrease in volume, and when the pressure decreases, towards an increase in volume.

A change in pressure has virtually no effect on the volume of solid and liquid substances, i.e. does not change their concentration. Consequently, the equilibrium of reactions in which gases do not participate is practically independent of pressure.

! The course of a chemical reaction is influenced by substances - catalysts. But when using a catalyst, the activation energy of both the forward and reverse reactions decreases by the same amount and therefore the balance does not shift.

Solve problems:

No. 1. Initial concentrations of CO and O 2 in the reversible reaction

2CO (g) + O 2 (g)↔ 2 CO 2 (g)

Equal to 6 and 4 mol/l, respectively. Calculate the equilibrium constant if the concentration of CO 2 at the moment of equilibrium is 2 mol/l.

No. 2. The reaction proceeds according to the equation

2SO 2 (g) + O 2 (g) = 2SO 3 (g) + Q

Indicate where the equilibrium will shift if

a) increase the pressure

b) increase the temperature

c) increase the oxygen concentration

d) introduction of a catalyst?