Ch 4 covers chemical kinetics — rate of reaction, factors affecting rate, rate law, order, molecularity, integrated rate equations, half-life, and the Arrhenius equation linking rate constant to temperature.
Rate = −d[R]/dt = d[P]/dt. Rate law: Rate = k[A]ⁿ[B]ᵐ (determined experimentally). Order = n + m. Molecularity: number of molecules in elementary step (always whole number). Order can be 0, fractional, or negative.
Zero order: [A] = [A]₀ − kt, t½ = [A]₀/2k. First order: ln[A] = ln[A]₀ − kt, t½ = 0.693/k (independent of [A]₀). Second order: 1/[A] = 1/[A]₀ + kt.
k = Ae^(−Ea/RT). A = frequency factor, Ea = activation energy. Higher T → more molecules cross Ea → faster reaction. Catalyst lowers Ea. ln(k₂/k₁) = (Ea/R)(1/T₁ − 1/T₂).
Download: https://ncert.nic.in/textbook/pdf/lech104.pdf | Part I: https://ncert.nic.in/textbook/pdf/lech1ps.zip
Order is experimentally determined and can be 0, fractional, or negative. Molecularity is the number of molecules participating in an elementary step — always a positive integer (1, 2, or rarely 3). For complex reactions, order ≠ molecularity. For elementary reactions, they are equal.
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