The ΔH (enthalpy change) and ΔS (entropy change) will be less than zero for adsorption of gas on solid surface, i.e. ΔH<0,ΔS<0. Entropy change ( ΔS ) The randomness of the gas molecules decreases as they are adsorb on solid surface due to restriction in their motion. ∴ ∆S is negative. Enthalpy change (ΔH) Adsorption of gas on solid surface is an exothermic process, as there is force of attraction between adsorbate and adsorbent. ∴ ∆H is negative.