Question

During the spontaneous adsorption of a gas on the surface of a solid, which of the following is true?

• A. $△G<0$, $△H<0$, $△S<0$
• B. $△G<0$, $△H>0$, $△S<0$
• C. $△G<0$, $△H<0$, $△S>0$
• D. $△G>0$, $△H<0$, $△S<0$

Answer 1

The correct option is A $△G<0$, $△H<0$, $△S<0$

Adsorption is a spontaneous process, and we know for a spontaneous process $△G<0$.
Adsorption decreases the residual forces (i.e. surface energy) acting along the surface of adsorbent. So, adsorption is accompanied by decrease in enthalpy of system (exothermix process). Hence $△H<0$.
During adsorption the randomness of the system decreases. So $△S<0$.