Question

Difference between physical adsorption and chemical adsorption.

Answer 1

Hint: ‘ad’ – to attract or hold molecules together to a surface, ‘Sorption’ – process of being adhered to the medium or, adsorption and absorption simultaneously.
- Physical adsorption – changes due to adsorption externally
- Chemical adsorption - changes due to adsorption internally

Complete step by step answer:
Adsorption is a surface phenomenon where atoms or molecules from gas or liquid are stuck onto the surface.
> Adsorbate – substance that is adsorbed.
> Adsorbent – the medium on which substance is adsorbed

Property	Physical adsorption / physisorption / van der Waals adsorption	chemisorption or chemical adsorption or activated adsorption
Force of attraction	The force of attraction between adsorbent and adsorbate is van der Waals force (weak force)	The force of attraction between adsorbent and adsorbate is chemical forces (strong force)
Temperature condition	Occurs at low temperature	Occurs at high temperature
specificity	Almost all gases show this type of adsorption at low temperature, it is non-specific in nature.	Very few gases show this adsorption ,it is highly specific in nature.
Enthalpy of adsorption	Enthalpy of adsorption is very low and less than 20-40 kJ/mol	Enthalpy of adsorption is very high and lies between 80 to 240kJ/mol
Attainment of equilibrium	It attains equilibrium very rapidly on changing temperature and pressure of the system	This is relatively slower
Reversible / irreversible	This is reversible in nature	This is usually irreversible in nature
Energy of activation	Energy of activation involved is very low	Energy of activation is very high.
Number of layers involved	It forms a multimolecular layer.	It forms a unimolecular layer.

Note: Do not confuse between adsorption and absorption. Adsorption is a surface phenomenon whereas absorption is a bulk phenomenon. Sorption and desorption are exactly opposite to each other.