Q29 · CSIR-NET Chemistry, December 2012

Paper: CSIR-NET December 2012 · Subject: Physical Chemistry · Chapter: Chemical Kinetics · Topic: Rate Laws Order · Marks: 2 · Difficulty: Hard

The rate equation for the reaction $2\mathrm{AB}+\mathrm{B_2} \rightarrow 2\mathrm{AB_2}$ is given by
\[ \text{rate}=k[\mathrm{AB}][\mathrm{B_2}] \]
A possible mechanism consistent with this rate law is
(a)$2\mathrm{AB}+\mathrm{B_2} \xrightarrow{\text{slow}} 2\,\mathrm{AB_2}$
(b)
\[ \begin{array}{l} \mathrm{AB+AB} \rightleftharpoons \mathrm{A_2B_2}\ \text{(fast)} \\ \mathrm{A_2B_2+B_2} \xrightarrow{\text{slow}} 2\,\mathrm{AB_2} \end{array} \]
(c)
\[ \begin{array}{l} \mathrm{AB+B_2} \xrightarrow{\text{slow}} \mathrm{AB_3} \\ \mathrm{AB_3+AB} \xrightarrow{\text{fast}} 2\,\mathrm{AB_2} \end{array} \]
(d)
\[ \begin{array}{l} \mathrm{AB+B_2} \rightleftharpoons \mathrm{AB_3}\ \text{(fast)} \\ \mathrm{AB_3+AB} \xrightarrow{\text{slow}} 2\,\mathrm{AB_2} \end{array} \]
Answer
Answer: C ✓ checked by 4AB · confidence high
Explanation
A slow first step AB + B₂ → AB₃ followed by fast AB₃ + AB → 2AB₂ gives rate = k[AB][B₂] (c).

Study loop for Chemical Kinetics

1. Practise the PYQsPrevious-year questions, with answers

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