Question

adsorption of gas on solid surface is generally exthemic because:

Answer 1

solid don't have enough moleculer space among its particles so that particles of gas can diffuse in.

Answer 2

This causes a decrease in the surface energy of absorbent. therefore absorbent is always exthemic. when a gas is obsorbed on a solid surface it's movement is restricted leading to a decrease in the enthorphy of the gas.