Question

Which of the following statements is correct for the spontaneous adsorption of a gas?

(a) ΔS is negative and, therefore ΔH should be highly positive.

(b) ΔS is negative and therefore, ΔH should be highly negative.

(c) ΔS is positive and therefore, ΔH should be negative.

(d) ΔS is positive and therefore, ΔH should also be highly positive.

Answer 1

Ans: (b) $ΔS$ is negative and therefore, $ΔH$ should be highly negative.

Sol: Using Gibb's-Helmholtz equation,

$ΔG = ΔH - TΔS$

During adsorption of a gas, entropy decreases $i.e. \text{ }ΔS < 0$

For spontaneous adsorption, $ΔG$ should be negative, which is possible when $ΔH$ is highly negative.