Chemical equilibrium is the basis of reversible chemical reactions

2024 Author: Angel Austin | [email protected]. Last modified: 2023-12-17 05:14

According to one of the classifications used to describe chemical processes, there are two types of opposite reactions - reversible and

irreversible. A reversible reaction does not go to completion, i.e. none of the substances entering it is completely consumed and does not change the concentration. Such a process ends with the establishment of a balance or chemical equilibrium, which is denoted by ⇌. But the forward and reverse reactions go on and on, without stopping, so the equilibrium is called dynamic or mobile. The onset of chemical equilibrium indicates that the forward reaction occurs at the same rate (V1) as the reverse (V2), V1 \u003d V2. If the pressure and temperature are constant, then the equilibrium in this system can last indefinitely.

Quantitatively, the chemical equilibrium is described by the equilibrium constant, which is equal to the ratio of the constants of direct (K1) and reverse (K2) reactions. It can be calculated using the formula: K=K1/K2. The indicators of the equilibrium constant will depend on the composition of the reactants andtemperature.

The shift of chemical equilibrium occurs according to Le Chatelier's principle, which sounds like this: "If external factors act on a system that is in equilibrium, then the balance will be disturbed and shifted in the direction opposite to this change."

Let's consider the chemical equilibrium and the conditions for its shift using the example of the formation of an ammonia molecule: N2 + 3H2 ↔ 2NH3 + Q.

Considering the equation of this reaction, we establish:

1. direct reaction is a compound reaction, because from 2 simple substances, 1 complex (ammonia) is formed, and the reverse - decomposition;
2. direct reaction proceeds with the formation of heat, therefore it is exothermic, therefore, the reverse is endothermic and proceeds with the absorption of heat.

Now consider this equation under the condition of modifying certain parameters:

1. Change in concentration. If we increase the concentration of the initial substances - nitrogen and hydrogen - and reduce the amount of ammonia, then the equilibrium will shift to the right to form NH3. If you need to move it to the left, increase the concentration of ammonia.
2. Increase in temperature will move the equilibrium towards a reaction in which heat is absorbed, and when it is lowered, it is released. Therefore, if the temperature is increased during the synthesis of ammonia, then the equilibrium will shift towards the starting products, i.e. to the left, and with a decrease in temperature - to the right, towards the reaction product.

3. If you increasepressure, then the equilibrium will shift to the side where the amount of gaseous substances is less, and with a decrease in pressure - to the side where the amount of gases increases. In the synthesis of NH3 from 4 mol of N2 and 3H2, 2 NH3 is obtained. Therefore, if the pressure is increased, then the equilibrium will move to the right, to the formation of NH3. If the pressure is reduced, then the equilibrium will shift towards the original products.

   

We conclude that the chemical equilibrium can be disturbed by increasing or decreasing:

1. temperature;
2. pressure;
3. concentration of substances.

When a catalyst is introduced into any reaction, the balance does not change, i.e. chemical equilibrium is not disturbed.