Chapter 9 – Surface Chemistry (JEE)
1. Introduction to Surface Chemistry
Surface chemistry deals with the study of chemical phenomena that occur at the surfaces or interfaces.
Surface area plays a crucial role because reactions occur at surfaces.
Examples of interfaces:
- Solid–Gas
- Solid–Liquid
- Liquid–Gas
- Liquid–Liquid
2. Adsorption
Adsorption is the accumulation of particles (atoms, ions or molecules) at the surface of a solid or liquid.
Adsorption is a surface phenomenon, whereas absorption is a bulk phenomenon.
3. Types of Adsorption
| Physical Adsorption | Chemical Adsorption |
|---|---|
| Weak Van der Waals forces | Strong chemical bonds |
| Reversible | Irreversible |
| Low heat of adsorption | High heat of adsorption |
| Occurs at low temperature | Occurs at high temperature |
4. Factors Affecting Adsorption
- Nature of adsorbent
- Surface area of adsorbent
- Nature of gas
- Pressure
- Temperature
5. Adsorption Isotherm
Adsorption isotherm represents the relationship between amount adsorbed and pressure at constant temperature.
6. Freundlich Adsorption Isotherm
$$\frac{x}{m} = kP^{1/n}$$
$$\log\left(\frac{x}{m}\right) = \log k + \frac{1}{n}\log P$$
Limitations:
- Valid only at low pressure
- Fails at high pressure
7. Langmuir Adsorption Isotherm
Langmuir proposed that adsorption occurs on fixed number of identical sites.
$$\frac{x}{m} = \frac{aP}{1 + bP}$$
Assumptions:
- Monolayer adsorption
- No interaction between adsorbed molecules
8. Catalysis
Catalysis is the phenomenon in which the rate of a chemical reaction is increased by the presence of a catalyst.
A catalyst remains chemically unchanged at the end of reaction.
9. Types of Catalysis
- Homogeneous catalysis
- Heterogeneous catalysis
- Enzyme catalysis
10. Mechanism of Heterogeneous Catalysis
Steps:
- Adsorption of reactants
- Formation of activated complex
- Desorption of products
11. Shape-Selective Catalysis
Zeolites are used as shape-selective catalysts.
Example: Conversion of alcohols into petrol.
12. Colloids
Colloids are heterogeneous systems in which one substance is dispersed in another.
13. Types of Colloids
| Dispersed Phase | Dispersion Medium | Example |
|---|---|---|
| Solid | Liquid | Sol |
| Liquid | Gas | Aerosol |
| Gas | Liquid | Foam |
14. Preparation of Colloids
- Dispersion methods
- Condensation methods
15. Properties of Colloids
- Tyndall effect
- Brownian movement
- Electrical properties
- Coagulation
16. Emulsions
Emulsions are colloidal systems of two immiscible liquids.
Types:
- Oil in water (O/W)
- Water in oil (W/O)
17. Emulsifying Agents
Substances that stabilize emulsions are called emulsifying agents.
18. Applications of Surface Chemistry
- Gas masks
- Industrial catalysis
- Medicines
- Detergents
- Food industry
19. Common JEE Traps
- Confusing adsorption and absorption
- Misinterpreting isotherm graphs
- Forgetting assumptions of Langmuir model
- Wrong classification of colloids
20. Final Revision Checklist
You are exam-ready if you can:
- Differentiate physisorption and chemisorption
- Derive Freundlich equation
- Explain catalysis mechanism
- Classify colloids correctly
- Answer assertion–reason questions