Consider the reaction,
`Cl_(2)(aq) + H_(2)S(aq) rarr S(s) + 2H^(+) (aq) + 2Cl^(-)(aq)`
The rate equation for this reaction is,
Rate `=k [Cl_(2)][H_(2)S]`
Which of these mechanisms is`//`are consistent with this rate equation ?
(I) `Cl_(2) + H_(2)S rarr H^(+) + Cl^(-) + Cl^(+) + HS^(-)` (slow)
`Cl^(+) + HS^(-) rarr H^(+) + Cl^(-) + S` (fast)
(II) `H_(2)S hArr H^(+) +HS^(-)` (fast equilibrium)
`Cl^(+) + HS^(-) rarr 2 Cl^(-) + H^(+) + S` (slow)

Options

A. (II) only
B. Both (I) and (II)
C. Neither (I) nor (II)
D. (I) only

Answer

D

Explanation

Slowest step is the rate determining step. Thus, in case (I), rate law is given as rate `= k[Cl_(2)][H_(2)S]`
While for the reaction given in case (II), rate law is given as rate `= k[H_(2)S][Cl_(2)][H^(+)]^(-1)`.
Hence, only mechanism (I) is consistent with the given rate law.