Give the difference between physical and chemical adsorption?

Physical Absorption

Chemical Absorption

1)      Caused by intermolecular van der waal’s forces.

Caused by chemical bond formation

2)      Depends on nature of gas. Easily liquefiable gases are adsorbed readily.

Much more specific and depends upon the nature of both the adsorbate and adsorbent.

3)      Heat of adsorption is small

Very large heat of adsorption

4)      It is reversible

It is irreversible

5)      Forms multimolecular layers on adsorbent surface.

Forms unimolecular layer.

6)      Occurs at low temperature; decreases with increase in temperature

Increase with increase of temperature.

7)      Increase of pressure increases adsorption.

High pressure is favourable. Decrease of pressure does not cause desorption.

8)      Equilibrium is attained readily and it is reversible.

Equilibrium is attained slowly and mostly not reversible.