Physical adsorption:-

1. Enthalpy of adsorption usually is the order of 20-40 kJ mol^-1.

2. Moles of adsorbate and adsorbent are held by Van der Waals interactions.

3. It usually takes place at low temperature and decreases with increasing temperature.

4. It is not very specific i.e., all gases are adsorbed at all solids to some extent.

5. Multi-molecular layers may be formed on the adsorbent.

6. It does not require any activation energy.

7. The amount of adsorbed in related to the case of liquefaction of the gas.

8. It is reversible in nature.

Chemical adsorption:-

1. Enthalpy of adsorption is of the order 40-400 kJ mol^-1

2. Molecules of adsorbate and adsorbent are held by chemical bonds.

3. It takes place are relatively high temperatures.

4. It is highly specific and takes place when there is some possibility of compound formation between the adsorbent molecules.

5. Usually mono-molecular layer is formed on the adsorbent.

6. It requires activation energy.

7. There is no such correlation.

8. It is irreversible in nature.