Chemical Equilibrium is the state in which both the reactants and products are present in concentrations that have no further tendency to change with time so that there is no observable change in the properties of the system. This state results when the forward reaction proceeds at the same rate as the reverse reaction. The reaction rates of the forward and backward reactions are generally not zero, but they are equal. Thus, there are no net changes in the concentrations of the reactants and products. Such a state is known as dynamic equilibrium. There are several factors like temperature, pressure, and concentration of the system which affect equilibrium.
Types of Chemical Equilibrium
There are two types of chemical equilibrium:
Homogenous Chemical Equilibrium
It can be further divided into two types: Reactions in which the number of molecules of the products is equal to the number of molecules of the reactants. For example,
- H2 (g) + I2 (g) ⇌ 2HI (g)
- N2 (g) + O2 (g) ⇌ 2NO (g)
Reactions in which the number of molecules of the products is not equal to the total number of reactant molecules. For example,
- 2SO2 (g) + O2 (g) ⇌ 2SO3 (g)
- COCl2 (g) ⇌ CO (g) + Cl2 (g)
Heterogeneous Chemical Equilibrium
In this type, the reactants and the products of chemical equilibrium are present in different phases. A few examples of heterogeneous equilibrium are listed below.
- CO2 (g) + C (s) ⇌ 2CO (g)
- CaCO3 (s) ⇌ CaO (s) + CO2 (g)
Thus, the different types of chemical equilibrium are based on the phase of the reactants and products.
⇒ Check: Ionic Equilibrium
It is useful in many industrial processes like,
- Preparation of ammonia by Haber’s process: In this nitrogen combines with hydrogen to form ammonia, the yield of ammonia is more at low temperature, high pressure, and in the presence of iron as catalyst.
- Preparation of sulphuric acid by contacts process: In this process, the fundamental reaction is the oxidation of sulfur dioxide into sulfur trioxide. This involves chemical balance.