Question

During Adsorption of a gas on a solid

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

Answer 1

Answer: (A)

When a gas is adsorbed on a solid surface, its movement is restricted leading to a decrease in the entropy of the gas i.e. $\Delta S$ is negative. Now, we know that, for a process to be spontaneous, $\Delta G$ should be negative.

We know, $\Delta G=\Delta H-T\Delta S$

Since $\Delta S$ is negative, $\Delta H$ has to be negative so as to make $\Delta G$ negative. Hence adsorption is always an exothermic process.