Physisorption
(Physical adsorption)
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1. Caused by intermolecular Vander Waal’s forces.
2. Depends on nature of gas. Easily liquefiable gases are adsorbed readily.
3. Heat of adsorption is small (about 5 kcal per mol)
4. Reversible
5. Forms multimolecular layers on adsorbent surface.
6. Occurs at low temperature; decreases with increase in temperature.
7. Increase of pressure increases adsorption
8. Equilibrium is attained readily and it is reversible. |
| Chemisorption
(Chemical adsorption)
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Caused by chemical bond formation.
Much more specific and depends upon the nature of the both the adsorbate and adsorbent.
Very large (20-100 kcal per mol).
Irreversible
Forms unimolecular layer.
Increases with increase of temperature
High pressure is favourable. Decrease of pressure does not cause desorption.
Equilibrium is attained slowly and mostly not reversible. |
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