Chemical Kinetics – NEET Chemistry Class 12

Chemical Kinetics studies the rate of chemical reactions and the factors affecting them. This chapter is highly scoring in NEET as it includes conceptual questions, numerical problems, and real-life applications. Understanding kinetics allows students to predict reaction speed and mechanism.

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Introduction to Chemical Kinetics

• Reaction rate: Change in concentration of reactants or products per unit time

• Expressed as: Rate = –Δ[A]/Δt = Δ[B]/Δt

• Key aspects: Initial rate, average rate, and instantaneous rate

• Importance:

  • Predicts how fast a reaction occurs

  • Helps in designing industrial processes

  • Explains reaction mechanisms

Factors Affecting Rate of Reaction

1. Concentration of Reactants – Higher concentration generally increases rate.

2. Temperature – Higher temperature increases kinetic energy, thus increasing rate.

3. Catalysts – Lower activation energy and speed up reactions without being consumed.

4. Pressure – Significant in gaseous reactions.

5. Surface Area – Greater surface area increases reaction rate for solids.

Rate Law and Order of Reaction

• Rate Law: Rate = k[A]^m[B]^n

  • k = rate constant, m/n = order of reaction w.r.t reactants

• Overall Order: Sum of powers of concentration terms in rate law

• Zero, First, Second Order Reactions:

  • Zero order: Rate independent of concentration

  • First order: Rate ∝ [A]

  • Second order: Rate ∝ [A]^2 or [A][B]

• Half-life (t½): Time required for concentration to reduce to half

  • First order: t½ = 0.693/k

Temperature Dependence and Arrhenius Equation

• Arrhenius Equation: k = A e^(–Ea/RT)

  • k = rate constant, A = frequency factor, Ea = activation energy, R = gas constant, T = temperature

• Explains how temperature affects reaction rate

• Important for predicting reaction rates in chemical and biological systems

Collision Theory and Molecularity

• Collision Theory: Reaction occurs when reactant molecules collide with proper orientation and energy ≥ Ea

• Molecularity: Number of molecules involved in an elementary reaction

  • Unimolecular, bimolecular, termolecular

Importance for NEET Preparation

• Questions often include rate law calculations, order of reaction, half-life, and temperature effects.

• Understanding concepts and numerical practice is crucial for NEET.

• Collision theory and molecularity questions are asked for conceptual clarity.

Previous Year NEET Questions – Insights

• Determining rate constant and reaction order from experimental data

• Calculating half-life and concentrations at different times

• Applying Arrhenius equation to find activation energy

• Conceptual questions on factors affecting reaction rate and catalyst function

Study Tips for Students

1. Memorize Rate Laws and Formulas – t½, k, Arrhenius equation

2. Practice Numerical Problems – Rate, half-life, order, and activation energy calculations

3. Understand Conceptual Questions – Collision theory, molecularity, effect of temperature/catalyst

4. Refer NCERT Examples – NEET frequently bases questions on NCERT

5. Solve Previous Year Questions – Reinforces conceptual clarity and improves speed

Conclusion

Mastering Chemical Kinetics is essential for NEET success. It helps students analyze reaction rates, solve numerical problems, and understand reaction mechanisms. A strong grasp of kinetics ensures confidence in both theoretical and application-based NEET questions.