CBSE Class 12 Chemistry Absorbtion Memory map

This CBSE Class 12 Chemistry concept map covers adsorption and absorption from the Surface Chemistry chapter. It explains the difference between physisorption and chemisorption, adsorbate and adsorbent, sorption, the factors affecting adsorption, adsorption isotherms and isobars, the applications of adsorption, and the thermodynamics that decides when adsorption occurs.

Adsorption, Absorption and Sorption

Molecular species in Gas or Liquid form accumulate in the bulk rather than at the surface of a Solid or Liquid → Absorption
Molecular species in Gas or Liquid form accumulate at the surface of a Solid or Liquid rather than in its bulk → Adsorption
Absorption and adsorption both take place simultaneously → Sorption

Gas or Liquid species that accumulate on the surface → ADSORBATE
Solid or Liquid surface on which the adsorbate accumulates → ADSORBENT

Desorption is the reverse of adsorption. It takes place on heating or on reducing pressure.

Types of Adsorption

Physisorption
Due to van der Waals' force of attraction
Which is: Specific, Reversible, Associated with low enthalpy

Chemisorption
Due to chemical bond
Which is not: Specific, Reversible, Associated with low enthalpy

Cause of Adsorption

Adsorption is due to the presence of unbalanced or residual attractive forces at the surface of the adsorbent.

Factors Affecting Adsorption

For a given adsorbate and adsorbent, adsorption depends upon:
Nature of the gas
Nature of the adsorbent
Temperature
Pressure of gas adsorbate

The graph of x/m versus:
Temperature at constant pressure → Adsorption isobar
Pressure at constant temperature → Adsorption isotherm

Applications of Adsorption

Adsorption finds application in:
1. Creating and preserving vacuum
2. Gas mask
3. Decolourization of sugar
4. Chromatography
5. Heterogeneous catalysis
6. Adsorption indicator
7. Softening of hard water
8. Dehumidifier
9. Separation of inert gases
10. Froth flotation process
11. Painting
12. Dyeing
13. Water conservation
14. Curing diseases

Thermodynamics of Adsorption

Adsorption is exothermic, i.e., ΔH = -ve.
That is why the randomness or freedom of movement of the gas adsorbed on the solid decreases, so the entropy change is ΔS = -ve.

For adsorption to occur, ΔG must be negative.
ΔG = ΔH - TΔS

This helps us to understand the temperature dependence of adsorption:
At low temperature: -ΔH is greater than TΔS; ΔG = -ve, adsorption occurs.
At high temperature: -ΔH is less than TΔS; ΔG = +ve, adsorption does not occur, desorption occurs.
At a certain temperature: -ΔH = TΔS; ΔG = 0, equilibrium state.

[Figure: Concept map titled ADSORPTION, linking ADSORBATE, ADSORBENT, DESORPTION, ABSORPTION, SORPTION, PHYSISORPTION and CHEMISORPTION, with the factors affecting adsorption, the isobar and isotherm graphs, the list of applications and the thermodynamic conditions as described above]