What is the difference between physical adsorption and chemisorption ?

Physical Adsorption

Chemisorption

1.

The forces operating in these cases are weak van der Waal’s forces.

1.

The forces operating in these cases are similar to those of a chemical bond.

2.

The heats of adsorption are low, i.e. about 20-40 kJmol^-1.

2.

The heats of adsorption are high, i.e. about 40 – 400 kJmol^-1

3.

The process is reversible, i.e. desporption of the gas occurs by increasing the temperature or decreasing the pressure.

3.

The process is irreversible.

4.

It does not require any activation energy.

4.

It requires activation energy.

5.

This types of adsorption usually takes place at low temperature and decreases with increases of temperature.

5.

This type of adsorption first increases with increase of temperature. The effect is called activated adsorption.

6.

The amount of the gas absorbed is related to the ease of liquification of the gas.

6.

There is no such correlation.

7.

It forms multimolecular layer.

7.

It forms unimolecular layer.