Question

Write three differences between physisorption and chemisorption.

Write two important differences between physical adsorption and chemisorption.

Write any two features which distinguish physisorption from chemisorption.

Give the main points of difference between physical and chemical adsorption.

What is the difference between physisorption and chemisorption?

Answer 1

Sr. No.	Points	Physisorption (Physical adsorption)	Chemisorption (Chemical adsorption)
1.	Nature of forces	The absorbate molecules are held to the surface of an absorbent by weak van Der Waal’s forces.	The absorbate molecules are held to the surface of an absorbent by chemical bonds.
2.	Specificity	This process is generally non-specific, meaning it does not depend on the characteristics of either the absorbate or the absorbent.	It is highly specific in nature, i.e., it depends on the nature of the absorbate and absorbent.
3.	Enthalpy of adsorption	The enthalpy of adsorption in physisorption is low, typically around 20-40 kJ/mol, because only weak forces are involved.	The enthalpy of adsorption in chemisorption is high, usually in the range of 80-200 kJ/mol, due to the formation of chemical bonds.
4.	Temperature dependence	Physisorption is favored at low temperatures; as temperature increases, the extent of adsorption decreases.	Chemisorption is favored at higher temperatures; the extent of adsorption increases with temperature up to an optimum level.
5.	Layer formation	In physisorption, multiple layers of adsorbate molecules may form on the surface of the adsorbent.	In chemisorption, usually only a single layer (monolayer) of adsorbate molecules forms due to bond saturation.
6.	Activation energy	Physisorption typically does not require any activation energy or requires very little.	Chemisorption requires significant activation energy to initiate the chemical bonding.