$word_{count}$: 200

Chemical kinetics contributes ~4% of JEE Main marks. High-yield topics: (1) First-order calculations — master k = $\frac{2.303}{t}$log($\frac{a}{a-x}$), $t_1$/2 = 0.693/k, fraction remaining = $\frac{1}{2}$^n. These appear almost every year. (2) Arrhenius equation — ln$\frac{k2}{k1}$ = $\frac{Ea}{R}$(1/T1 - 1/T2) for Ea calculation. Know R = 8.314 $\frac{J}{mol.K}$, convert kJ to J. (3) Order determination from initial rates data — systematic comparison of experiments. (4) Gas-phase pressure problems — write $P_A$ in terms of $P_0$ and $P_t$ correctly. Common mistakes: (a) confusing molecularity with order, (b) using stoichiometric coefficients as orders for complex reactions, (c) forgetting to convert Ea from kJ to J in Arrhenius calculations, (d) sign errors in 1/T1 - 1/T2, (e) using wrong log base (ln vs log — factor of 2.303). Quick checks: k must have correct units for the order. First-order half-life is independent of concentration. Rate always decreases with time (except zero order where it stays constant). A catalyst changes k but not $K_{eq}$.