Question

Predict the sign of the entropy change for each of the following reactions

Answer 1

a) C (graphite ) → C (diamond)

The entropy decreases in the above conversion because diamond has a more orderly arrangement of atoms as compared to graphite. So the entropy will have a negative sign.

(b) electrolysis of NaCl solution

On electrolysis of an aqueous solution of NaCl we will obtain hydrogen gas at cathode and chlorine gas at the anode. Thus, the state of the system is changing from the liquid state to the gaseous state, and the degree of randomness in gases is more than that in liquids. Therefore the change in entropy will have a positive sign.

(c) Sublimation of camphor

Camphor exists in the solid state. On sublimation, it changes from the solid state into the vapour state, and we know that degree of randomness is more in vapour state than in the solid state. So the change in entropy will be positive.

(d)

In the above reaction, one molecule of CaCO3 is giving a molecule of CaO and a molecule of CO2, which is in the gaseous phase. Thus the degree of randomness will increase here. So the change in ΔS will have a positive sign.