The correct statement(s) pertaining to the adsorption of a gas on a solid surface is (are)

Options

A. Adsorption is always exothermic
B. Physisorption may transform into chemisorption at high temperature
C. Physisorption increase with increasing temperature but chemisorption decreases with increasing temperature
D. Chemisorption is more exothermic than physisorption, however it is very slow due to higher energy of activation.

Answer

A, D

Explanation

Heat is evolved in both physical and chemical adsorption.
further, Chemical adsorption leads to the formation of surface compound. The forces involved are similar to those of chemical bond. This is confirmed by the fact that heats evolved during chemisorption are high (220-400 kJ `mol^(-1)`) while the heat evolved during physisorption is 20-40 kJ `mol^(-1)`.