A mechanism for the reaction is proposed: (i) (fast), (ii) (slow), (iii) (fast). What is the overall — Chemical Kinetics Chemistry Question
Question
A mechanism for the reaction $X_2 + Y_2 \rightarrow 2XY$ is proposed: (i) $X_2 \rightleftharpoons 2X$ (fast), (ii) $X + Y_2 \rightarrow XY + Y$ (slow), (iii) $X + Y \rightarrow XY$ (fast). What is the overall order of this reaction?
Answer: B
💡 Solution & Explanation
From the slow step, $\text{Rate} = k_2[X][Y_2]$. From the fast equilibrium, $K_{eq} = [X]^2/[X_2] \Rightarrow [X] = (K_{eq}[X_2])^{1/2}$. Substituting this gives $\text{Rate} = k'[X_2]^{1/2}[Y_2]^1$. Overall order = $1 + 0.5 = 1.5$.
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