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

Answer 2

$\Delta G = \Delta$ H - TAS .As gas is adsorbed on surface of solid, entropy decreases, i.e.$\Delta$S < 0. Therefore, for $\Delta$G < 0, AH must be negative.