Overview of Chemical Equilibrium

Chemical Equilibrium:

When the rates of forward and reverse reactions are equal, the concentration of the reactants and products remains constant. This stage is called chemical equilibrium.

Characteristics of Chemical Equilibrium:

Constancy of concentration
Can be initiated from the other side
Can’t be attained in an open vessel
A catalyst cannot change the equilibrium point.
Values of equilibrium constant do not depend upon the initial concentration of reactants
At equilibrium, ∆G= O

Types of Chemical Equilibrium:

Homogeneous
Heterogeneous

Homogeneous :

In this reaction, both the reactants and products involved in chemical equilibrium are present in the same phase.

It can also be categorized into two types:

(1) Reactions where the number of product molecules matches the number of reactant molecules.

For example,

H₂(g) + I₂(g) ⇌ 2HI(g)

N₂(g) + O₂(g) ⇌ 2NO(g)

(2) Reactions where the number of product molecules does not match the total number of reactant molecules can occur. For example,

2SO₂(g) + O₂(g) ⇌ 2SO₃(g)

COCl₂(g) ⇌ CO(g) + Cl₂(g)

Heterogeneous :

In this kind of reaction, the reactants and the products at chemical equilibrium exist in different phases. For example,

CO₂(g) + C(s) ⇌ 2CO(g)

CaCO₃(s) ⇌ CaO(s) + CO₂(g)

Constant of Chemical Equilibrium:

A certain ratio of reactant and product concentration has a constant value for a reversible reaction at equilibrium and a constant temperature. This is called the equilibrium constant, denoted by ‘K.’