COMPARISON OF PHYSICAL ADSORPTION AND CHEMISORPTION

COMPARISON OF PHYSICAL ADSORPTION AND CHEMISORPTION
Physical adsorption
1. Caused by intermolecular van der Waal’s
forces.
2. Depends on nature of gas. Easily liquefiable
gases are adsorbed readily.
3. Heat of adsorption is small (about 5 kcal
mol
–1
).
4. Reversible.
5. Occurs rapidly at low temperature; decreases
with increasing temperature.
6. Increase of pressure increases adsorption;
decrease of pressure causes desorption.
7. Forms multimolecular layers on adsorbent
surface.
In chemisorption, the adsorbed layer of gas is one-molecule thick since chemical combination

Chemisorption
1. Caused by chemical bond formation.
2. Much more specific than physical
adsorption.
3. Heat of adsorption is large (20–100 kcal
mol
–1
).
4. Irreversible.
5. Increases with increase of temperature.
6. Change of pressure has no such effects.
7. Forms unimolecular layer.

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