JEE Main 2025 Jan 29 Shift 1, Chemistry Q14: Reactions of Various Orders

JEE Main2025Jan 29, Shift 1Chemistry

The reaction $A_{2} + B_{2} \to 2 AB$ follows the mechanism

$A_{2} k_{- 1} ⇌ k_{1} A + A (fast)$

$A + B_{2} ⟶ k_{2} AB + B (slow)$

$A + B \to AB (fast)$

The overall order of the reaction is :

Solution

The slow step sets the rate: $rate = k_{2} [A] [B_{2}] .$

From the fast pre-equilibrium, $K = \frac{k _{1}}{k _{- 1}} = \frac{[ A ] ^{2}}{[ A _{2} ]}$ , hence $[A] = K [A_{2}] .$

Substituting: $rate = k_{2} K [A_{2}]^{1/2} [B_{2}] .$

Overall order $= \frac{1}{2} + 1 = 1.5$ .

Concept behind this question

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