A mechanism for the reaction is given as: (i) (fast equilibrium), (ii) (slow). Which is the correct — Chemical Kinetics Chemistry Question
Question
A mechanism for the reaction $2NO + Cl_2 \rightarrow 2NOCl$ is given as: (i) $NO + Cl_2 \rightleftharpoons NOCl_2$ (fast equilibrium), (ii) $NOCl_2 + NO \rightarrow 2NOCl$ (slow). Which is the correct rate law derived from this mechanism?
Answer: B
💡 Solution & Explanation
The slow Rate Determining Step dictates $\text{Rate} = k_{slow}[NOCl_2][NO]$. Using the fast equilibrium step, $K_{eq} = [NOCl_2] / ([NO][Cl_2])$, isolating the intermediate yields $[NOCl_2] = K_{eq}[NO][Cl_2]$. Substituting this gives $\text{Rate} = (k_{slow}K_{eq})[NO]^2[Cl_2] = k_{overall}[NO]^2[Cl_2]$.
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