Question

What is the difference between physical adsorption and chemisorption ?

Answer 1

Physisorption	Chemisorption
Weak van der Waals’ forces present.	Strong chemical bond forces present.
Low; of the order of 20-40 kJ/mol.	High; of the order of 80-240 kJ/mol.
Usually occurs at low temperature.	Occurs at high temperature.
Reversible.	Irreversible.
It is not specific in nature, i.e. all gases may be adsorbed on the surface of a solid.	It is highly specific in nature and occurs only when there is bond formation between adsorbent and adsorbate molecules.
Forms multi-molecular layers under high pressure.	Forms mono-molecular layer.
The extent of adsorption is directly related with the ease of liquefaction of the gas.	There is no correlation between extent of adsorption and the ease of liquefaction of the gas.
It does not involve appreciable activation energy. In most cases, the activation energy required is almost nil.	It generally requires appreciable activation energy since a chemical reaction is to take place.
Same state as in the bulk.	May be quite different from that in the bulk.