Towards the reaction products. Chemical balance. Variety of chemical processes

Task

Indicate how it will affect:

a) increase in pressure;

b) increase in temperature;

c) an 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(G). Let us determine the volumes of gaseous substances before and after the reaction using stoichiometric coefficients:

According to Le Chatelier's principle, with increasing pressure , the balance shifts towards educationI substances occupying less o b b we 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, as the temperature rises, the balance shifts towards the endothermic reaction (- Q ), i.e. towards the reverse reaction - the decomposition reaction of CO 2 (←) , because according to the law of conservation of energy:

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

V) With increasing oxygen concentration the equilibrium of the system shifts towards the production of CO 2 (→) becausean increase in the concentration of reactants (liquid or gaseous) shifts towards products, i.e. towards direct reaction.

Additionally:

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

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

if volume gas mixture reduce by three times? In which direction will the equilibrium of the system shift?

Solution. Let us denote the concentrations of reactants: [SO 2 ]= a , [ABOUT 2 ] = b , [ SO 3 ] = With. According to the law of mass velocityv direct and reverse reactions before volume changes:

v etc = Ka 2 b

v arr. = TO 1 With 2 .

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

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 rate of the reverse reaction by only nine times. The balance of the system has shifted towards educationSO 3 .

Example 2. Calculate how many times the rate of a reaction occurring in the gas phase will increase when the temperature increases 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 empirical Van't Hoff 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 (g) + N 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 =3 mol/l, [H 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 problem statement 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 concentration [CO 2 ] R = X mol/l. According to the equation of the system, the number of moles of hydrogen formed will also beX mol/l. The same number of moles (X mol/l) CO and H 2 O is spent for educationX moles CO 2 and N 2 . Therefore, the equilibrium concentrations of all four substances are:

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

[CO] R = (3 – X ) mol/l;

[H 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;

[H 2 ] R = 1.2 mol/l;

[CO] R = 3 – 1.2 = 1.8 mol/l;

[H 2 ABOUT] R = 2 – 1.2 = 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 problem statement, the equilibrium constant is equal to 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 required:

υ reacted (CO) = υ (CO 2) = 0.16 mol

υ reacted (O 2) = 1/2υ (CO 2) = 0.08 mol

Hence,

υ initial = υ reacted + υ equilibrium

υ initial (CO) = 0.16 +0.2 = 0.36 mol

υ initial (O 2) = 0.08 +0.32 = 0.4 mol

Substance			CO2
From original	0,36
C reacted	0,16	0,08	0,16
C equilibrium		0,32	0,16

Example 5.Determine the equilibrium concentration of HI in the system

H 2 (g) + I 2 (g) ↔ 2HI (g) ,

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

Solution. Let x mol/l be formed at some point in time HI

Substance	H 2	I 2
from source , mol/l
with pro-react. , mol/l	x/2	x/2
c equal , mol/l	1-x/2	PCl 5 (g) = RS l 3 (d) + WITH l 2(G); Δ N= + 92.59 kJ. How to change: a) temperature; b) pressure; c) concentration to shift the equilibrium towards a direct reaction - decompositionPCl 5 ? Solution. A displacement or shift in chemical equilibrium is a change in the equilibrium concentrations of reacting substances as a result of a change in one of the reaction conditions. The direction in which the equilibrium has shifted is determined by Le Chatelier’s principle: a) since the decomposition reactionPCl 5 endothermic (Δ N > 0) then to shift the equilibrium towards the direct reaction it is necessary to increase the temperature; b) since in this system the decomposition 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) a shift in equilibrium in the indicated direction can be achieved by increasing the concentration of RSl 5 , and a decrease in the concentration of PCl 3 or Cl 2 .

Chemical equilibrium- the state of the system when the direct and reverse reactions have the same speed.. During the process with a decrease in the starting substances, the speed of the direct chemical. the reaction decreases, and the rate of the reverse reaction increases with increasing CHI. At some point in time, the speed of forward and reverse chemistry. reactions are equal. The state of the system does not change until external factors (P, T, c) act. Quantitatively, the state of equilibrium is characterized using the equilibrium constant. Equilibrium constant – Constant , reflecting the ratio of concentrations of components of a reversible reaction in a state of chemical equilibrium. (depends only on C). For each, we reverse the chem. reactions in specific conditions seem to characterize the limit to which the chemical goes. reaction. .K=.If (concentration ref) - no reaction; if equilibrium shifts to the right - does not proceed. The equilibrium constant does not change its value with changes in the concentration of reactants. The fact is that a change in concentration only leads to a shift in chemical composition. balance in one direction or another. In this case, a new equilibrium state is established at the same constant . True Balance can be shifted to one side or another by the action of any factors. But when these factors are canceled, the system returns to its original state. False- the state of the system is unchanged over time, but when external conditions change, an irreversible process occurs in the system (In the dark, H 2 + Cl 2 exists, when illuminated, HCl forms. When lighting stops, H 2 and Cl 2 will not return). A change in at least one of these factors leads to to a shift in equilibrium. The influence of various factors on the state of a chemical equation is qualitatively described by the principle of shifting equilibrium by Le Chatelier (1884: with any external influence on a system that is in a state of chemical equilibrium, processes occur in it that lead to a decrease in this influence.

Equilibrium constant

The equilibrium constant shows How many times is the rate of the forward reaction greater or less than the rate of the reverse reaction?

Equilibrium constant is the ratio of the product of the equilibrium concentrations of reaction products, taken to the power of their stoichiometric coefficients, to the product of the equilibrium concentrations of the starting substances, taken to the power of their stoichiometric coefficients.

The value of the equilibrium constant depends on the nature of the reactants and temperature, and does not depend on the concentration at the moment of equilibrium, since their ratio is always a constant value, numerically equal to the equilibrium constant. If a homogeneous reaction occurs between substances in solution, then the equilibrium constant is denoted K C, and if between gases, then K R.

where Р С, Р D, Р А and Р В are the equilibrium pressures of the reaction participants.

Using the Clapeyron-Mendeleev equation, it is possible to determine the relationship between K P and K C

Let's move the volume to the right side

p = RT, i.e. p = CRT (6.9)

Let us substitute equation (6.9) into (6.7) for each reagent and simplify

, (6.10)

where Dn is the change in the number of moles of gaseous reaction participants

Dn = (c + d) – (a + c) (6.11)

Hence,

K P = K C (RT) Dn (6.12)

From equation (6.12) it is clear that K P = K C if the number of moles of gaseous participants in the reaction does not change (Dn = 0) or there are no gases in the system.

It should be noted that in the case of a heterogeneous process, the concentration of the solid or liquid phase in the system is not taken into account.

For example, the equilibrium constant for a reaction of the form 2A + 3B = C + 4D, provided that all substances are gases and has the form

and if D is solid, then

The equilibrium constant has a large theoretical and practical significance. The numerical value of the equilibrium constant allows us to judge the practical possibility and depth of the chemical reaction.

10 4, then the reaction is irreversible

Equilibrium shift. Le Chatelier's principle.

Le Chatelier's principle (1884): if a system that is in stable chemical equilibrium is influenced from the outside by changing temperature, pressure or concentration, then the chemical equilibrium shifts in the direction in which the effect of the effect is reduced.

It should be noted that the catalyst does not shift the chemical equilibrium, but only accelerates its onset.

Let us consider the influence of each factor on the shift in chemical equilibrium for a general reaction:

aA + bB = cC + d D±Q.

Effect of changes in concentration. According to Le Chatelier's principle, an increase in the concentration of one of the components of an equilibrium chemical reaction leads to a shift in equilibrium towards an intensification of the reaction in which the chemical processing of this component occurs. Conversely, a decrease in the concentration of one of the components leads to a shift in the equilibrium towards the formation of this component.

Thus, an increase in the concentration of substance A or B shifts the equilibrium in the forward direction; an increase in the concentration of substance C or D shifts the equilibrium in the opposite direction; a decrease in the concentration of A or B shifts the equilibrium in the opposite direction; a decrease in the concentration of substance C or D shifts the equilibrium in the forward direction. (Schematically you can write: C A or C B ®; C C or C D ¬; ¯ C A or C B ¬; ¯ C C or C D ®).

Effect of temperature. The general rule determining the effect of temperature on equilibrium has the following formulation: an increase in temperature promotes a shift in equilibrium towards the endothermic reaction (- Q); a decrease in temperature promotes a shift in equilibrium towards the exothermic reaction (+ Q).

Reactions that occur without thermal effects do not shift chemical equilibrium when temperature changes. An increase in temperature in this case only leads to a more rapid establishment of equilibrium, which would have been achieved in a given system without heating, but over a longer time.

Thus, in an exothermic reaction (+ Q), an increase in temperature leads to a shift in the equilibrium in the opposite direction, and, conversely, in an endothermic reaction (- Q), an increase in temperature leads to a shift in the forward direction, and a decrease in temperature in the opposite direction. (Schematically we can write: at +Q Т ¬; ¯Т ®; at -Q Т ®; ¯Т ¬).

Effect of pressure. As experience shows, pressure has a noticeable effect on the displacement of only those equilibrium reactions in which gaseous substances participate, and at the same time, the change in the number of moles of gaseous reaction participants (Dn) is not equal to zero. As the pressure increases, the equilibrium shifts towards the reaction that is accompanied by the formation of fewer moles of gaseous substances, and as the pressure decreases, towards the formation of a larger number of moles of gaseous substances.

Thus, if Dn = 0, then pressure does not affect the displacement of the chemical equilibrium; if Dn< 0, то увеличение давления смещает равновесие в прямом направлении, уменьшение давления в сторону обратной реакции; если Dn >0, then an increase in pressure shifts the equilibrium in the opposite direction, and a decrease in pressure shifts it towards the forward reaction. (Schematically we can write: at Dn = 0 P has no effect; at Dn<0 ­Р®, ¯Р¬; при Dn >0 Р ¬, ¯Р ®). Le Chatelier's principle is applicable to both homogeneous and heterogeneous systems and provides a qualitative characteristic of the equilibrium shift.

Codifier Topics: reversible and irreversible reactions. Chemical balance. Shift in chemical equilibrium under the influence of various factors.

If a reverse reaction is possible, chemical reactions are divided into reversible and irreversible.

Reversible chemical reactions - these are reactions whose products under given conditions can interact with each other.

For example, ammonia synthesis is a reversible reaction:

N2 + 3H2 = 2NH3

The process occurs at high temperature, under pressure and in the presence of a catalyst (iron). Such processes are usually reversible.

Irreversible reactions - these are reactions whose products cannot interact with each other under given conditions.

For example, combustion reactions or reactions that occur with an explosion are most often irreversible. Carbon combustion proceeds irreversibly:

C + O 2 = CO 2

More details about classification of chemical reactions can be read.

The likelihood of product interaction depends on the process conditions.

So, if the system open, i.e. exchanges with environment both matter and energy, then chemical reactions in which, for example, gases are formed, will be irreversible.

For example , when calcining solid sodium bicarbonate:

2NaHCO 3 → Na 2 CO 3 + CO 2 + H 2 O

gas is released carbon dioxide and evaporate from the reaction zone. Therefore, this reaction will be irreversible under these conditions.

If we consider closed system , which can not exchange a substance with the environment (for example, a closed box in which the reaction occurs), then carbon dioxide will not be able to escape from the reaction zone, and will interact with water and sodium carbonate, then the reaction will be reversible under these conditions:

2NaHCO 3 ⇔ Na 2 CO 3 + CO 2 + H 2 O

Let's consider reversible reactions. Let the reversible reaction proceed according to the scheme:

aA + bB ⇔ cC + dD

The rate of direct reaction according to the law of mass action is determined by the expression:

v 1 =k 1 ·C A a ·C B b

Feedback speed:

v 2 =k 2 ·C С с ·C D d

Here k 1 And k 2 are the rate constants of the forward and reverse reactions, respectively, C A, C B, C C, C D– concentrations of substances A, B, C and D, respectively.

If at the initial moment of the reaction there are no substances C and D in the system, then particles A and B collide and interact predominantly, and a predominantly direct reaction occurs.

Gradually, the concentration of particles C and D will also begin to increase, therefore, the rate of the reverse reaction will increase. At some point the rate of the forward reaction will be equal to the rate of the reverse reaction. This state is called chemical equilibrium .

Thus, chemical equilibrium is a state of the system in which the rates of forward and reverse reactions are equal .

Since the rates of forward and reverse reactions are equal, the rate of formation of reagents is equal to the rate of their consumption, and the current concentrations of substances do not change . Such concentrations are called equilibrium .

Please note that at equilibrium Both forward and reverse reactions occur, that is, the reactants interact with each other, but the products also interact with each other at the same rate. At the same time, external factors can influence displace chemical equilibrium in one direction or another. Therefore, chemical equilibrium is called mobile, or dynamic .

Research in the field of mobile equilibrium began in the 19th century. The works of Henri Le Chatelier laid the foundations of the theory, which was later generalized by the scientist Karl Brown. The principle of mobile equilibrium, or the Le Chatelier-Brown principle, states:

If a system in a state of equilibrium is influenced by an external factor that changes any of the equilibrium conditions, then processes in the system aimed at compensating for the external influence are intensified.

In other words: when there is an external influence on the system, the equilibrium will shift so as to compensate for this external influence.

This principle, which is very important, works for any equilibrium phenomena (not just chemical reactions). However, we will now consider it in relation to chemical interactions. In the case of chemical reactions, external influences lead to changes in the equilibrium concentrations of substances.

Chemical reactions in a state of equilibrium can be influenced by three main factors - temperature, pressure and concentrations of reactants or products.

1. As is known, chemical reactions are accompanied by a thermal effect. If the direct reaction occurs with the release of heat (exothermic, or +Q), then the reverse reaction occurs with the absorption of heat (endothermic, or -Q), and vice versa. If you raise temperature in the system, the equilibrium will shift so as to compensate for this increase. It is logical that in an exothermic reaction the temperature increase cannot be compensated. Thus, as the temperature increases, the equilibrium in the system shifts towards heat absorption, i.e. towards endothermic reactions (-Q); with decreasing temperature - towards an exothermic reaction (+Q).

2. In the case of equilibrium reactions, when at least one of the substances is in the gas phase, the equilibrium is also significantly affected by a change pressure in system. As pressure increases, the chemical system tries to compensate for this effect and increases the rate of reaction, in which the amount of gaseous substances decreases. As the pressure decreases, the system increases the rate of reaction, which produces more molecules of gaseous substances. Thus: with an increase in pressure, the equilibrium shifts towards a decrease in the number of gas molecules, and with a decrease in pressure - towards an increase in the number of gas molecules.

Note! Systems where the number of molecules of reactant gases and products are the same are not affected by pressure! Also, changes in pressure have virtually no effect on the equilibrium in solutions, i.e. on reactions where there are no gases.

3. Also, equilibrium in chemical systems is affected by changes concentrations reactants and products. As the concentration of reactants increases, the system tries to use them up and increases the rate of the forward reaction. As the concentration of reagents decreases, the system tries to produce them, and the rate of the reverse reaction increases. As the concentration of products increases, the system also tries to consume them and increases the rate of the reverse reaction. When the concentration of products decreases, the chemical system increases the rate of their formation, i.e. rate of forward reaction.

If in chemical system the rate of forward reaction increases right , towards the formation of products And reagent consumption . If the rate of reverse reaction increases, we say that the balance has shifted left , towards food consumption And increasing the concentration of reagents .

For example, in the ammonia synthesis reaction:

N 2 + 3H 2 = 2NH 3 + Q

An increase in pressure leads to an increase in the rate of reaction, in which fewer gas molecules are formed, i.e. direct reaction (the number of molecules of reactant gases is 4, the number of gas molecules in products is 2). As pressure increases, the equilibrium shifts to the right, towards the products. At temperature rise the balance will shift in the opposite direction of the endothermic reaction, i.e. to the left, towards the reagents. An increase in the concentration of nitrogen or hydrogen will shift the equilibrium towards their consumption, i.e. to the right, towards the products.

Catalyst does not affect balance, because accelerates both forward and reverse reactions.

Chemical equilibrium is inherent reversible reactions and is not typical for irreversible chemical reactions.

Often, when implementing chemical process, the initial reactants are completely converted into reaction products. For example:

Cu + 4HNO 3 = Cu(NO 3) 2 + 2NO 2 + 2H 2 O

It is impossible to obtain metallic copper by carrying out the reaction in the opposite direction, because given the reaction is irreversible. In such processes, reactants are completely converted into products, i.e. the reaction proceeds to completion.

But the bulk of chemical reactions reversible, i.e. the reaction is likely to occur in parallel in the forward and reverse directions. In other words, the reactants are only partially converted into products and the reaction system will consist of both reactants and products. System in in this case is in a state chemical equilibrium.

In reversible processes, initially the direct reaction has maximum speed, which gradually decreases due to a decrease in the number of reagents. The reverse reaction, on the contrary, initially has a minimum speed, which increases as products accumulate. Eventually, a moment comes when the rates of both reactions become equal—the system reaches a state of equilibrium. When equilibrium occurs, the concentrations of the components remain unchanged, but chemical reaction it does not stop. That. – this is a dynamic (moving) state. For clarity, here is the following figure:

Let's say there is a certain reversible chemical reaction:

a A + b B = c C + d D

then, based on the law of mass action, we write down expressions for straightυ 1 and reverseυ 2 reactions:

v1 = k 1 ·[A] a ·[B] b

v2 = k 2 ·[C] c ·[D] d

Able chemical equilibrium, the rates of forward and reverse reactions are equal, i.e.:

k 1 ·[A] a ·[B] b = k 2 ·[C] c ·[D] d

we get

TO= k 1 / k 2 = [C] c [D] d ̸ [A] a [B] b

Where K =k 1 / k 2 – equilibrium constant.

For anyone reversible process, under given conditions k is a constant value. It does not depend on the concentrations of substances, because When the amount of one of the substances changes, the amounts of other components also change.

When the conditions of a chemical process change, the equilibrium may shift.

Factors influencing the shift in equilibrium:

• changes in concentrations of reagents or products,
• pressure change,
• temperature change,
• adding a catalyst to the reaction medium.

Le Chatelier's principle

All of the above factors influence the shift in chemical equilibrium, which obeys Le Chatelier's principle: If you change one of the conditions under which the system is in a state of equilibrium - concentration, pressure or temperature - then the equilibrium will shift in the direction of the reaction that counteracts this change. Those. equilibrium tends to shift in a direction leading to a decrease in the influence of the influence that led to a violation of the state of equilibrium.

So, let us consider separately the influence of each of their factors on the state of equilibrium.

Influence changes in concentrations of reactants or products let's show with an example Haber process:

N 2(g) + 3H 2(g) = 2NH 3(g)

If, for example, nitrogen is added to an equilibrium system consisting of N 2 (g), H 2 (g) and NH 3 (g), then the equilibrium should shift in a direction that would contribute to a decrease in the amount of hydrogen towards its original value, those. in the direction of the formation of additional ammonia (to the right). At the same time, the amount of hydrogen will decrease. When hydrogen is added to the system, the equilibrium will also shift towards the formation of a new amount of ammonia (to the right). Whereas the introduction of ammonia into the equilibrium system, according to Le Chatelier's principle , will cause a shift in equilibrium towards the process that is favorable for the formation of starting substances (to the left), i.e. The ammonia concentration should decrease through the decomposition of some of it into nitrogen and hydrogen.

A decrease in the concentration of one of the components will shift the equilibrium state of the system towards the formation of this component.

Influence pressure changes makes sense if gaseous components take part in the process under study and there is a change in the total number of molecules. If total number molecules remain in the system permanent, then the change in pressure does not affect on its balance, for example:

I 2(g) + H 2(g) = 2HI (g)

If the total pressure of an equilibrium system is increased by decreasing its volume, then the equilibrium will shift towards decreasing volume. Those. towards decreasing the number gas in system. In reaction:

N 2(g) + 3H 2(g) = 2NH 3(g)

from 4 gas molecules (1 N 2 (g) and 3 H 2 (g)) 2 gas molecules are formed (2 NH 3 (g)), i.e. the pressure in the system decreases. As a result, an increase in pressure will contribute to the formation of an additional amount of ammonia, i.e. the equilibrium will shift towards its formation (to the right).

If the temperature of the system is constant, then a change in the total pressure of the system will not lead to a change in the equilibrium constant TO.

Temperature change system affects not only the displacement of its equilibrium, but also the equilibrium constant TO. If additional heat is imparted to an equilibrium system at constant pressure, then the equilibrium will shift towards the absorption of heat. Consider:

N 2(g) + 3H 2(g) = 2NH 3(g) + 22 kcal

So, as you can see, the direct reaction proceeds with the release of heat, and the reverse reaction with absorption. As the temperature increases, the equilibrium of this reaction shifts towards the decomposition reaction of ammonia (to the left), because it appears and weakens the external influence - an increase in temperature. On the contrary, cooling leads to a shift in equilibrium in the direction of ammonia synthesis (to the right), because the reaction is exothermic and resists cooling.

Thus, an increase in temperature favors a shift chemical equilibrium towards the endothermic reaction, and the temperature drop towards the exothermic process . Equilibrium constants all exothermic processes decrease with increasing temperature, and endothermic processes increase.

A state in which the rate of a reverse reaction becomes equal speed direct reaction is called chemical equilibrium.

This condition is quantitatively characterized equilibrium constant. For a reversible reaction we can write it like this:

Where, in accordance with the law of mass action, is the rate of direct reaction v 1 and reverse v 2 will look like this:

v 1 = k 1 [A] m [B] n,

v 2 = k 2 [C] p [D] q .

At the moment of achievement chemical equilibrium the rates of forward and reverse reactions become the same:

k 1 [A] m [B] n = k 2 [C] p [D] q ,

K = k 1 /k 2 =([C] p [D] q)/([A] m [B] n),

Where TO- equilibrium constant showing the ratio of forward and reverse reactions.

Those concentrations that stop at equilibrium are called equilibrium concentrations. It should be remembered that the values ​​of the degrees m, n, p, q equal to the stoichiometric coefficients in the equilibrium reaction. The numerical value of the equilibrium constant determines the yield of the reaction. At K>>1 the yield of products is high, and when TO<<1 - very small.

Reaction output- the ratio of the amount of product actually obtained to the amount that would have been obtained if this reaction had proceeded to completion (expressed as a percentage).

Chemical equilibrium cannot be maintained indefinitely. In fact, changes in temperature, pressure or concentration of reactants can shift the equilibrium in one direction or another.

Changes occurring in the system as a result of external influences are determined by the principle of moving equilibrium - Le Chatelier's principle:

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.

Those. the ratio between the rates of forward and reverse reactions changes.

The principle applies not only to chemical, but also to physical processes, such as melting, boiling, etc.

Change in concentration.

As the concentration of one of the reactants increases, the equilibrium shifts towards the consumption of this substance.

As the concentration of iron or sulfur increases, the equilibrium will shift towards the consumption of this substance, i.e. to the right.

The influence of pressure on chemical equilibrium.

Only taken into account in gas phases!

As pressure increases, the equilibrium shifts towards decreasing amounts of gaseous substances. If the reaction proceeds without changing the amounts of gaseous substances, then pressure does not affect the equilibrium in any way.

N 2 (d) + 3H 2 (G)2 N.H. 3 (G),

There are 4 moles of gaseous reactants on the left, 2 on the right, so as the pressure increases, the equilibrium will shift to the right.

N 2 (d)+O 2 (g) = 2NO(G),

There are 2 moles of gaseous substances on the left and on the right, so pressure does not affect the equilibrium.

The influence of temperature on chemical equilibrium.

When the temperature changes, both the forward and reverse reactions change, but to varying degrees.

As the temperature increases, the equilibrium shifts towards the endothermic reaction.

N 2 (d) + 3H 2 (G) 2 N.H. 3 (d) +Q,

This reaction proceeds with the release of heat (exothermic), so an increase in temperature will shift the equilibrium towards the starting products (reverse reaction).