Question

Explain :

Dynamic nature of chemical equilibrium with suitable example.

Answer 1

Dynamic nature of chemical equilibrium :

i. Consider a chemical reaction : A ⇌ B.

K_C = [B]/[A]

At equilibrium,

The ratio of concentration of the product to that of the concentration of the reactant is constant and this is equal to K_C.

ii. At this stage reaction takes place in both the directions with same speed although the reaction appears to have stopped. 

Thus, 

The chemical equilibrium is dynamic in nature. 

Dynamic means moving and at a microscopic level, the system is in motion.

iii. For example, in the reaction between H₂ and I₂ to form HI, the colour of the reaction mixture becomes constant because the concentrations of H₂, I and HI become constant at equilibrium.

H₂ + I₂ ⇌ 2HI

Thus, 

When equilibrium is reached,

The reaction appears to have stopped. 

However, 

This is not the case. 

The reaction is still going on in the forward and backward direction but the rate of forward reaction is equal to the rate of backward reaction. 

Hence, 

Chemical equilibrium is dynamic in nature and not static.