Q. Consider the reaction, $Cl_{2}(aq) + H_{2}S(aq) \rightarrow S(s) + 2H^{+}(aq) + 2Cl^{-}(aq)$ the rate equation for this reaction is , rate = $k\left\lbrack Cl_{2} \right\rbrack\lbrack H_{2}S\rbrack$ Which of these mechanisms is/are consistent with this rate equation? $Cl_{2} + H_{2}S(aq) \rightarrow H^{+}Cl^{-} + Cl^{+} + HS^{-}(slow)$ $\ \ \ \ \ \ \ \ \ Cl^{+} + HS^{-} \rightarrow H^{+}Cl^{-} + S(fast)$ $H_{2}S \leftrightarrow H^{+} + HS^{-}(fast\ equilibrium)$ $\ \ \ \ \ \ \ \ Cl_{2} + HS^{-} \rightarrow 2Cl^{-} + H^{+}S(slow)$
A) (B) only
B) Both (A) and (B)
C) Neither (A) nor (B)
D) (A)Only
Explanation
(d)
Slowest step is rate determining step, thus, in case (A), rate law is given as $rate = k\left\lbrack Cl_{2} \right\rbrack\lbrack H_{2}S\rbrack$
While for the reaction given in case (B), rate law is given as rate$= \ k\left\lbrack H_{2}S \right\rbrack\left\lbrack Cl_{2} \right\rbrack\left\lbrack H^{+} \right\rbrack^{- 1}$
Hence, only mechanism (A) is consistent with give rate law.
Reviewed by Dr. Abubacker
Physics Educator & NEET/JEE Specialist
Ph.D. in Physics with 19+ years of teaching experience.