Question

Spontaneous adsorption of a gas on solid surface is an exothermic process because

(a) ΔH increases for system 

(b) ΔS increases for gas 

(c) ΔS decreases for gas 

(d) ΔG increases for gas

Answer 1

The correct option is (c) ΔS decreases for gas.

Explanation:

For spontaneous adsorption process, standard Gibb's free energy (ΔG) must be negative as well as the degree of randomness of gas molecule on the surface of solid decreases. For exothermic process, ΔH must be negative. Hence, with the help of following equation :

ΔH = ΔG + TΔS

TΔS is negative. 

Thus, during this adsorption ΔS decreases.