Chapter 3 — Chemical Kinetics

Chapter 3 of the Class 12 Chemistry NCERT textbook, "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.

• Measuring and expressing reaction rate — The chapter defines average and instantaneous rates and builds the rate law and rate constant, showing that how fast a reaction goes must be found by experiment rather than read off the balanced equation.
• Order versus molecularity — It carefully separates order — an experimental quantity that can be zero or fractional — from molecularity, which applies only to single elementary steps, and uses integrated rate equations to track concentration over time for zero- and first-order reactions.
• Why temperature and catalysts matter — The Arrhenius equation and collision theory explain the strong temperature dependence of rate and why a reaction needs both enough activation energy and correct molecular orientation, while a catalyst speeds things up by opening a lower-energy pathway.

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