1. Chemistry

2. Session
Surface Chemistry - 1

3. Session Objectives Adsorption Adsorption versus absorption
Types of adsorption: physisorption and chemisorption
Desorption
Adsorption isotherms: Freundlich adsorption isotherms
Application

4. Adsorption
The phenomenon of higher concentration of any molecular species at the surface than in the bulk
Adsorbent
The substance on the surface of which adsorption takes place is called adsorbent
Adsorbate
The substance which is being adsorbed on the surface of another substance.
Desorption
The process of removal of an adsorbed substance from the surface on which it is absorbed

5. Adsorbent Materials Activated Carbon Activated Alumina Silica Gel
Molecular Sieves (Zeolites)
Polar and Non-polar adsorbents

6. Adsorption vs absorption

7. Types of Adsorption
Positive adsorption occurs when the concentration of adsorbate is higher on the surface of adsorbent than in the bulk.
Negative adsorption occurs when the concentration of adsorbate is less on the surface of adsorbent than in the bulk.

8. Types of adsorption
Physical adsorption
Chemical adsorption

9. Factors affecting adsorption
Effect of adsorbate: The easily liquifiable gases like NH3, HCl, CO2 etc. are adsorbed to a greater extent than the permanent gases such as H2 ,O2, N2, etc.
Effect of specific area of the absorbent: The greater the specific area of the solid, the greater would be its adsorbing capacity.
Effect of temperature:adsorption decreases with increase in temperature.
Effect of pressure: An increase in pressure causes an increase in the magnitude of adsorption of an adsorbent.

10. Freundlich Isotherm
A graph between the amount (x/m) adsorbed by an adsorbent and the equilibrium pressure of the adsorbate at constant temperature is called adsorption isotherm
At low pressure the graph is nearly straight line
At high pressure x/m becomes independent of p
Over a narrow range of p

11. Freundlich Isotherm

12. Adsorption isobar
Graph between the amount adsorbed(x/m) and temperature at a constant equilibrium pressure of adsorbate gas is known as adsorption isobar
Chemisorption isobar shows an initial increase with temperature and then expected decrease .The initial increase is because of the fact that the heat supplied acts as activation energy required in chemisorption.

13. Application of Adsorption
In clarification of sugar
In gas masks
In catalysis
In adsorption indicators
In chromatographic analysis
In softening of hard water
In preserving vacuum
In paint industry
In removing moisture from air in the storage of delicate instruments

14. Surender Kumar
PGT CHEM
Thank you