Types of Adsorption

TYPES OF ADSORPTION :

1.) Physical Adsorption ( Physisorption )

2.) Chemical Adsorption ( Chemisorption )

1.) PHYSICAL ADSORPTION ( PHYSISORPTION ) : 

a.) If the adsorbate is held on a surface of adsorbent by weak van der Waals forces, the adsorption is called physical adsorption or physisorption.

b.) It is non-specific.
c.) It is reversible.

d.)  The extent of adsorption increases with increase in surface area.

e.) There are weak van der Waals forces of attraction between adsorbate and adsorbent.

f.) It has low enthalpy of adsorption (20 – 40 kJ mol-1).

g.) Low temperature is favourable.
h.) No appreciable activation energy is needed.
i.) It forms multimolecular layers.

2.) CHEMICAL ADSORPTION ( CHEMISORPTION ) :

a.) If the forces holding the adsorbate are as strong as in chemical bonds, the adsorption process is known as chemical adsorption of chemisorption.
b.) It is highly specific.
c.) It is irreversible.

d.) It also increases with increase in surface area.
e.) There is strong force of attraction similar to chemical bond.
f.) It has high enthalpy of adsorption (180 – 240 kJ mol-1).
g.) High temperature is favourable.
h.) High activation energy is sometimes needed.
i.) It forms unimolecular layers.