Chapter 3 — Chemical Kinetics

Chemical Kinetics is the branch of chemistry that studies the rates of chemical reactions and the factors — concentration, temperature, pressure, and catalysts — that control how fast reactions proceed.

Class 12 Chemistry Chapter 3 covers chemical kinetics, the study of reaction rates and mechanisms. It explains average and instantaneous rates, rate law expressions, and the rate constant k. The chapter distinguishes between order of reaction (experimentally determined, can be zero or fractional) and molecularity (applicable only to elementary reactions, values 1–3). Integrated rate equations are derived for zero-order (kt = [R]0 − [R]) and first-order (k = 0.693/t½) reactions. Temperature dependence is described by the Arrhenius equation k = Ae^(−Ea/RT), and collision theory explains that effective collisions require both sufficient activation energy and proper molecular orientation.

1. 01Rate of reaction is measured as the change in concentration of a reactant or product per unit time, expressed in mol L⁻¹ s⁻¹
2. 02Rate law (Rate = k[A]^x[B]^y) must be determined experimentally; exponents need not equal stoichiometric coefficients
3. 03Order of a reaction is the sum of powers of concentration terms in the rate law; it can be zero, fractional, or a whole number
4. 04Half-life of a first-order reaction is t½ = 0.693/k, independent of initial concentration; for zero-order, t½ = [R]0/2k
5. 05The Arrhenius equation k = Ae^(−Ea/RT) shows that increasing temperature or lowering activation energy increases the rate constant
6. 06A catalyst increases reaction rate by providing an alternate pathway with lower activation energy, without altering the equilibrium constant