Surface Chemistry
Class 12 Complete Notes for NEET & Bihar Board
Comprehensive lecture notes covering all essential topics with important highlights for exam preparation
Introduction to Surface Chemistry
Surface chemistry deals with phenomena that occur at the surfaces or interfaces of substances. It involves the study of processes like adsorption, catalysis, and colloid formation which occur at the interface of two phases such as solid-liquid, solid-gas, liquid-gas, etc.
Interface: The boundary between two distinct phases (e.g., solid-liquid, liquid-gas). Surface chemistry specifically studies phenomena at these interfaces.
Adsorption
Adsorption is the process where molecules of a substance (gas or liquid) accumulate on the surface of a solid or liquid rather than in the bulk. The substance that gets adsorbed is called the adsorbate, and the surface on which adsorption occurs is called the adsorbent.
NEET Point: Distinguish between adsorption and absorption - Adsorption is surface phenomenon while absorption is bulk phenomenon.
Types of Adsorption
| Characteristic | Physical Adsorption (Physisorption) | Chemical Adsorption (Chemisorption) |
|---|---|---|
| Nature | Weak van der Waals forces | Strong chemical bonds |
| Specificity | Not specific | Highly specific |
| Enthalpy change | Low (20-40 kJ/mol) | High (80-240 kJ/mol) |
| Temperature effect | Decreases with increase in temperature | Increases with increase in temperature |
| Reversibility | Reversible | Irreversible |
Adsorption Isotherms
Adsorption isotherms describe how the amount of adsorbate varies with pressure at constant temperature. The most common isotherms are:
Catalysis
A catalyst is a substance that increases the rate of a chemical reaction without itself undergoing any permanent chemical change. Catalysts work by providing an alternative reaction pathway with lower activation energy.
Bihar Board Focus: Types of catalysis - homogeneous, heterogeneous, and autocatalysis with examples.
Enzyme Catalysis
Enzymes are biological catalysts (proteins) that catalyze biochemical reactions in living organisms. They are highly specific and efficient under mild conditions of temperature and pH.
Colloids
Colloids are heterogeneous mixtures where one substance is dispersed as very fine particles in another substance. The size of colloidal particles ranges from 1 nm to 1000 nm.
| Property | True Solution | Colloidal Solution | Suspension |
|---|---|---|---|
| Particle Size | < 1 nm | 1 nm - 1000 nm | > 1000 nm |
| Visibility | Invisible | Visible under ultramicroscope | Visible to naked eye |
| Diffusion | Rapid | Slow | Does not diffuse |
| Filtration | Pass through filter paper | Pass through filter paper | Do not pass |
Emulsions, Gels, and Aerosols
Emulsions: Colloidal dispersion of liquid in liquid (e.g., milk, oil in water).
Gels: Colloidal system where liquid is dispersed in solid (e.g., cheese, jelly).
Aerosols: Colloidal dispersion of liquid/solid in gas (e.g., fog, smoke).
Applications of Surface Chemistry
- Industrial catalysts for chemical manufacturing
- Adsorption in pollution control and gas masks
- Colloids in food industry, medicines, and photography
- Enzyme catalysis in biological processes and industry
- Froth flotation for mineral processing
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