Question

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

• A. $\Delta H$ increases for system
• B. $\Delta S$ increases for gas
• C. $\Delta S$ decreases for gas
• D. $\Delta G$ increases for gas

Answer 1

Answer: (C)

$\Delta S$ decreases for gas

Spontaneous adsorption of gas implies $\Delta G$ is negative.

The degree of randomness of gas molecules also decreases with adsorption. Hence, $\Delta S$ is also negative.

Therefore, $T$$\Delta S$ is $-ve$.

$\Delta H=\Delta G+T\Delta S$

Therefore, $\Delta H=-ve$.

Hence, spontaneous adsorption of a gas on a solid surface is an exothermic process because $\Delta S$ decreases for the system.