Chemistry Course Content for Class 12 – Chemical Kinetics:

Chemical Kinetics

Introduction

Chemical kinetics is the branch of chemistry that deals with the study of the rate of chemical reactions and the factors affecting them. It helps us understand how fast reactants are converted into products.

Learning Outcomes

Students will be able to:

Define the rate of a chemical reaction.

Explain factors affecting reaction rates.

Understand rate law and rate constant.

Differentiate between reaction order and molecularity.

Analyze zero-order and first-order reactions.

Explain collision theory and activation energy.

Key Concepts

1. Rate of a Chemical Reaction

The change in concentration of reactants or products per unit time.

Rate = Change in concentration / Time

Unit: mol L⁻¹ s⁻¹

2. Factors Affecting Reaction Rate

Nature of reactants

Concentration of reactants

Temperature

Surface area

Pressure (for gases)

Presence of catalysts

3. Rate Law

The rate of a reaction is proportional to the concentration of reactants raised to suitable powers.

Rate = k[A]ᵐ[B]ⁿ

Where:

k = Rate constant

m, n = Orders with respect to reactants

4. Order of Reaction

The sum of the powers of concentration terms in the rate law.

Example: Rate = k[A]²[B]

Order = 2 + 1 = 3

5. Molecularity

The number of reacting species taking part in an elementary reaction.

Types:

Unimolecular

Bimolecular

Termolecular

6. Integrated Rate Equations

Zero-Order Reaction

Rate = k

Characteristics:

Rate is independent of concentration.

Concentration decreases linearly with time.

First-Order Reaction

Rate = k[A]

Characteristics:

Rate depends on concentration.

Half-life is constant.

7. Half-Life Period (t½)

Time required for the concentration of a reactant to become half of its initial value.

8. Temperature Dependence of Rate

As temperature increases, reaction rate increases due to more effective collisions.

9. Arrhenius Equation

Relates rate constant with temperature and activation energy.

10. Collision Theory

Chemical reactions occur when reactant particles collide with:

Sufficient energy

Proper orientation

11. Activation Energy

Minimum energy required for reactants to undergo a successful reaction.

12. Catalysts

Substances that alter the rate of a reaction without being consumed.

Functions:

Lower activation energy

Increase reaction rate

Applications of Chemical Kinetics

Food preservation

Industrial chemical production

Drug manufacturing

Environmental chemistry

Corrosion control

Quick Recap

✔ Rate of reaction

✔ Factors affecting rate

✔ Rate law and rate constant

✔ Order and molecularity

✔ Zero-order and first-order reactions

✔ Half-life period

✔ Arrhenius equation

✔ Activation energy

✔ Collision theory

✔ Catalysis

HOTS Question

Why does refrigerated food spoil more slowly than food kept at room temperature?

Answer: Lower temperature decreases the kinetic energy of molecules, reducing the frequency of effective collisions and slowing down the rate of spoilage reactions.