CBSE Class 12 Chemistry Surface Chemistry Chapter Notes

 Chemistry Ch 5

Surface Chemistry

Top Concepts / Key learnings:

1. Adsorption: The accumulation of molecular species at the surface rather than in the bulk of a solid or liquid is termed as adsorption.

2. Adsorbate: The substance which is being adsorbed on the surface of another substance is called adsorbate.

3. Adsorbent: The substance present in bulk, on the surface of which adsorption is taking place is called adsorbent.

4. Desorption: The process of removing an adsorbed substance from a surface on which it is adsorbed is called desorption.

5. Absorption: It is the phenomenon in which a substance is uniformly distributed all over the surface.

6. Difference between adsorption and absorption: 

7. Sorption: When adsorption and absorption take place simultaneously, it is called sorption.

8. Enthalpy or heat of adsorption: Adsorption generally occurs with release in energy, i.e., it is exothermic in nature. The enthalpy change for the adsorption of one mole of an adsorbate on the surface of adsorbent is called enthalpy or heat of adsorption.

9. Types of adsorption:  

a. Physical adsorption or physisorption: 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. Chemical adsorption or chemisorption: If the forces holding the adsorbate are as strong as in chemical bonds, the adsorption process is known as chemical adsorption of chemisorption.

10. Difference between Physical and chemical adsorption:

11. Factors affecting adsorption of gases on solids:

a. Nature of adsorbate: Physical adsorption is non-specific in nature and therefore every gas gets adsorbed on the surface of any solid to a lesser or greater extent. However, easily liquefiable gases like NH₃. HCl, CO₂, etc. which have higher critical temperatures are absorbed to greater extent whereas H₂, O₂, N₂ etc. are adsorbed to lesser extent. The chemical adsorption being highly specific, therefore, a gas gets adsorbed. 

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