Question

Adsorption of gas on solid is accompanied by:

• A. Decrease in entropy of the system
• B. Decrease in enthalpy of the system
• C. Decrease in free energy of system
• D. No change in free energy of system

Answer 1

Answer: (A), (B), (C)

Decrease in free energy of system

As adsorption is exothermic process, it leads to a decrease in the residual force on the surface of the adsorbent. This cause a decrease in the surface energy of the adsorbent.
When gas adsorbed on the surface of solid, entropy decreases as when a gas is adsorbed, the freedom of movement of its molecules become restricted i.e., $\Delta S=-ve$. For a process to be spontaneous, $\Delta G$ must be negative. Since $\Delta S=-ve$, $\Delta H$ must be negative.