Question

what is the sign of change in enthalpy and change in entropy when a gas is adsorbed by an adsorbent

Answer 1

The change in enthalpy is denoted to be negative. The reason behind this is that when adsorbate molecules are adsorbed on the surface, freedom of movement of molecules become restricted and this results in a decrease in entropy. At constant temperature and pressure, adsorption occurs spontaneously.

Answer 2

Explanation:

Adsorption is accompanied by decrease in the free energy of the system as it is a spontaneous process. When ΔG becomes zero, adsorption equilibrium is established. Since it is an exothermic process, ΔH is negative. Since the adhering of gas molecules to the surface lowers the randomness, the ΔS is negative.