Menu

Chemical Kinetics

NCERT Class 12 Chemistry Chapter 3

Chemical Kinetics for Class 12 Chemistry, JEE and NEET: reaction rate, rate law, order, molecularity, zero and first order reactions, Arrhenius equation.

6 topics Updated 8 Nov 2026

For: Class 12, JEE and NEET, unless a topic says otherwise

In the syllabus: JEE Class 12 syllabus, NEET Class 12 syllabus

With your textbook

NCERT Chemistry Part I (Class 12), Chapter 3 “Chemical Kinetics”, reprint 2026-27.

Open the official NCERT chapter (PDF, 4.0 MB, ncert.nic.in)

Checked on 19 Oct 2026.

Learn in this order

  1. Rate of a chemical reaction

    Average and instantaneous rate, units, the balanced equation and partial pressures, with solved examples.

    NCERT Section 3.1 15 min read 5 solved examples 11 practice questions

  2. Factors influencing the rate of a reaction

    Factors affecting rate, rate law and rate constant, units of k, molecularity and the rate determining step.

    NCERT Section 3.2 17 min read 5 solved examples 11 practice questions

  3. Experiment: kinetics of the iodide–hydrogen peroxide reaction

    Iodide and HO in acid, the procedure, timing the blue with thiosulphate and starch, and the effect of iodide.

    JEE and NEET only 14 min read 5 solved examples 12 practice questions

  4. Integrated rate equations

    Zero and first order reactions, their graphs and half-lives, gas phase k and pseudo first order.

    NCERT Section 3.3 19 min read 6 solved examples 16 practice questions

  5. Temperature dependence of the rate of a reaction

    Effect of temperature on rate, activation energy, ln k against 1/T, Maxwell–Boltzmann curve and catalysts.

    NCERT Section 3.4 19 min read 5 solved examples 12 practice questions

  6. Collision theory of chemical reactions

    Collision frequency, effective collisions, threshold energy, orientation and the steric factor P.

    NCERT Section 3.5 16 min read 4 solved examples 8 practice questions

Key formulas in this chapter

Rate of a chemical reaction

  • r(av) = −Δ[R]/Δt = Δ[P]/Δt
  • r(inst) = −d[R]/dt = d[P]/dt
  • Rate = −(1/a)Δ[A]/Δt = (1/c)Δ[C]/Δt
  • Units: mol L s; gases atm s

Factors influencing rate

  • Rate = k[A][B]; order = x + y
  • Units of k: (mol L) s
  • Zero order: mol L s; first: s; second: L mol s; third: L mol s
  • 2NO + O → 2NO: rate = k[NO][O]

Experiment: iodide and hydrogen peroxide

  • 2I + HO + 2H → I + 2HO (slow)
  • I + 2SO → SO + 2I (fast)
  • Rate ≈ [SO]/(2t); rate ∝ 1/t
  • First order in I: t × [I] constant

Integrated rate equations

  • Zero order: [R] = [R] − kt
  • Zero order: t½ = [R]/2k
  • First order: k = (2.303/t) log([R]/[R])
  • First order: [R] = [R] exp(−kt)
  • First order: t½ = 0.693/k
  • Gas phase: k = (2.303/t) log[p/(2p − p)]

Temperature dependence of rate

  • k = A exp(−Ea/RT)
  • ln k = −Ea/RT + ln A
  • log(k/k) = (Ea/2.303R)(T − T)/(TT)
  • log k = log A − Ea/(2.303RT)
  • Fraction with E > Ea (NCERT) = exp(−Ea/RT)

Collision theory

  • Rate = ZAB exp(−Ea/RT)
  • Rate = P ZAB exp(−Ea/RT)
  • k = P zAB exp(−Ea/RT), so A ≈ P zAB (NCERT writes P ZAB)
  • Threshold energy = Ea + energy of the reactants
  • Fraction with E ≥ Ea (NCERT) = exp(−Ea/RT)

More in Chemistry