Chemical Kinetics Class 12 Notes, IIT-JEE & NEET

In JEE Main numericals, the two-temperature form of the Arrhenius equation is most commonly used: log(k₂/k₁) = (Ea/2.303R)(1/T₁ − 1/T₂). You are typically given two rate constants at two temperatures and asked to calculate activation energy. Always convert temperature to Kelvin and use R = 8.314 J mol⁻¹ K⁻¹.

The order of reaction is the sum of the powers to which reactant concentrations are raised in the experimentally determined rate law. It is found by the initial rate method — measuring how the rate changes as each reactant concentration is varied independently, while keeping others constant. Order can be zero, fractional, or a positive integer.

Chemical kinetics is the study of reaction rates and the factors that control them. In Class 12, the chapter covers rate laws, rate constants, order and molecularity, integrated rate equations for zero-order, first-order, and second-order reactions, half-life calculations, and the Arrhenius equation for temperature dependence of reaction rates.

Yes. JEE Advanced tests Chemical Kinetics through mechanism-based questions, multi-correct MCQs, and integer-type problems. Typical Advanced-level questions ask you to derive the rate law from a proposed mechanism, identify the rate-determining step, or interpret a complex graph. These require deeper conceptual understanding beyond NCERT, which is covered in eSaral's IIT Bombay faculty-led video lectures.

NEET most frequently tests: (1) factors affecting rate of reaction, (2) units of rate constant for different orders, (3) half-life of first-order reactions, (4) graphical identification of reaction order, and (5) the effect of a catalyst on activation energy. Together these five topic areas account for approximately 70–80% of NEET questions from this chapter based on 2019–2024 paper analysis.

The rate of reaction changes as the reaction proceeds (because reactant concentrations change), while the rate constant k is fixed for a given reaction at a given temperature. Rate = k[A]^x[B]^y — the rate depends on concentration, but k does not. Only temperature (and the presence of a catalyst) changes the value of k.

For a first-order reaction, t₁/₂ = 0.693/k, where k is the rate constant. The key feature is that this half-life is completely independent of the initial concentration of the reactant. This means the time taken for 50% of the reaction to complete is the same regardless of how much reactant you start with.