Describe the differences between physisorption and chemisorption.

Difference between physisorption and chemisorption are as follows.

Physisorption:

Due to Vander waal forces, adsorbate is held on the surface of adsorbent. Enthalpy of adsorption is low, that is, 20 kJ/mol. Physisorption is reversible in nature. It occurs at low temperature and decreases with increase in temperature. At the surface, multi-molecular layer of adsorbate occurs. There is no need of activation energy in physisorption. Also, it requires high pressure and decrease in pressure leads to desorption. All gases are adsorbed by adsorbent as physisorption is not specific.

Chemisorption:

Due to chemical bonds, molecules of adsorbate and adsorbent are held together. Enthalpy of adsorption is high, that is, 200 kJ/mol. It is irreversible in nature. It occurs ate relatively high temperature. Chemisorption leads to the formation of only monomolecular layers. It needs high activation energy. And, high pressure is favorable abd decrease in pressure does not cause desorption. Chemisorption is highly specific in nature.