difference between physisorption and chemisorption

The difference between Physisorption and Chemisorption are stated below.




Here adsorbate is held on the surface of adsorbent by van der Waals force.


Here molecules of adsorbate and adsorbent are held by chemical bonds.

Enthalpy of adsorption is comparatively low. ie, in the order of 20 kjmol-1.


Enthalpy of adsorption is high. ie, in the order of 200 kjmol-1.

It is reversible

It is irreversible

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

It takes place at relatively high temperature.

It is related to the case of liquefication of the gas. Easily liquefiable gases are more adsorbed. For example NH3, HCl etc are more adsorbed than permanent gases like He, O2, N2 etc.

It is not related.

Multi molecular layer of adsorbate occurs at the surface.

It forms only monomolecular layers.

It does not require any activation energy.

It requires high activation energy.

High pressure is favourable. Decrease of pressure causes desorption

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

It is not specific. ie, all gases are adsorbed by an adsorbent.

It is highly specific.

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physical adsoption is a non specific adsorption which is a reversible process .

chemical adsorption is highly specific and is an irreversible process.

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