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.