Topic: Elementary and complex reactions, order and molecularity· Chemical Kinetics

Mechanism of a hypothetical reaction X_2 + Y_2 → 2XY is given below :(i) X_2 → X + X (fast)(ii) X + Y_2 ⇌ XY + Y (slow)(iii) X + Y → XY (fast)The overall order of the reaction will be :

1. 2

2. 0

3. 1.5

4. 1

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Answer: 3. 1.5

Key idea: the rate law comes from the slow step; intermediates must be replaced using the fast equilibrium.

Rate = \(k[X][Y_2]\) (slow step). X is an intermediate formed in step (i), which is a fast equilibrium: \(K=\dfrac{[X]^2}{[X_2]}\), so \([X]=K^{1/2}[X_2]^{1/2}\).

Rate = \(k K^{1/2}[X_2]^{1/2}[Y_2]\). Order = \(\tfrac12 + 1 = 1.5\).

Doubtly AI · 30 Oct 2026 AI-generated · not yet verified Report

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Mechanism of a hypothetical reaction X_2 + Y_2 → 2XY is given below :(i) X_2 → X + X (fast)(ii) X + Y_2 ⇌ XY + Y (slow)(iii) X + Y → XY (fast)The overall order of the reaction will be :

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