Q. A hypothetical reaction $A_{2} + B_{2} \rightarrow 2AB$ follows the mechanism as given below, $A_{2} \rightleftharpoons A + A\ (fast)$ ${A + B}_{2} \longrightarrow AB + B$ (slow) $A + B \rightarrow AB$ (fast) The order of the overall reaction is
A) 2
B) 1
C) $1\frac{1}{2}$
D) 0
Explanation
(c)
From slow step, rate $= k{\lbrack B}_{2}\rbrack\lbrack A\rbrack$
From 1^{st} equation $k_{eq} = \frac{\lbrack A\rbrack^{2}}{\left\lbrack A_{2} \right\rbrack}$
$Or\ \lbrack A\rbrack = \sqrt{k_{eq}\lbrack A_{2}\rbrack} = k_{eq}^{1/2}A_{2}^{1/2}$
Hence, rate $= k{\lbrack B}_{2}\rbrack\ k_{eq}^{1/2}A_{2}^{1/2}$
$= k^{'}\left\lbrack A_{2} \right\rbrack^{1/2}\lbrack B_{2}\rbrack$
Hence, order
$= 1\frac{1}{2}$
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.