Question

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

• A. $\Delta S$ is negative and, therefore $\Delta H$ should be highly positive.
• B. $\Delta S$ is negative and therefore, $\Delta H$ should be highly negative.
• C. $\Delta S$ is positive and therefore, $\Delta H$ should be negative.
• D. $\Delta S$ is positive and therefore, $\Delta H$ should also be highly positive.

Answer 1

The correct option is B $\Delta S$ is negative and therefore, $\Delta H$ should be highly negative.

Using Gibb’s – Helmholtz equation,
$\Delta G=\Delta H-T\Delta S$
During adsorption of a gas, entropy decreases i.e. $\Delta S<0$
For spontaneous adsorption, $\Delta G$ should be negative, which is possible when $\Delta H$is highly negative.