A hypothetical chemical reaction obeys the following sequence: (i) (fast equilibrium, constant ); (ii) (slow, constant ); (iii) (fast). The overall apparent order of this complete reaction is:

Question

A hypothetical chemical reaction $X_2 + Y_2 \rightarrow 2XY$ obeys the following sequence: (i) $X_2 \rightleftharpoons 2X$ (fast equilibrium, constant $K$); (ii) $X + Y_2 \rightarrow XY + Y$ (slow, constant $k_2$); (iii) $X + Y \rightarrow XY$ (fast). The overall apparent order of this complete reaction is:

Prashant Kotian · Accepted Answer

Correct answer: B. The rate of the overall reaction is dictated exclusively by the slow step: . Since is an intermediate from the fast equilibrium, . Substituting this back gives . The total order is the sum of the exponents: .

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