Verified Solution • 2025–26 Session moderate

QJEEM10Chd587: JEE Main 2010 Chemistry - Class 12 JEEM10Chd587 Solution: Consider the reaction : Cl 2 (aq) + H 2 S(aq) → S(s) + 2H +…

Consider the reaction :

Cl2(aq) + H2S(aq) → S(s) + 2H+ (aq) + 2Cl– (aq)

The rate equation for this reaction is rate = k [Cl2] [H2S]

Which of these mechanisms is/are consistent with this rate equation?

(A) Cl2 + H2S →\to H+ + Cl– + Cl+ + HS– (slow)

Cl+ + HS– →\to H+ + Cl– + S (fast)

(B) H2S ⇔\Leftrightarrow H+ + HS– (fast equilibrium)

Cl2 + HS– →\to 2Cl– + H+ + S (slow)

Multiple Choice Options

  • A B only
  • B Both A and B
  • C Neither A nor B
  • D A only

Step-by-Step Verified Solution

Since the slow step is the rate determining step hence-

if we consider option (1)(1) we find

Rate =k[Cl2][H2S]= k\left[ {C{l_2}} \right]\left[ {{H_2}S} \right]

Now if we consider option (2)(2) we find

Rate =k[Cl2][HS−]     ...(1)= k\left[ {C{l_2}} \right]\left[ {H{S^ - }} \right]\,\,\,\,\,...\left( 1 \right)

From equation (i)(i)

k=[H+][HS−]H2Sk = {{\left[ {{H^ + }} \right]\left[ {H{S^ - }} \right]} \over {{H_2}S}}      \,\,\,\,\, or

[HS−]=k[H2S]H+\left[ {H{S^ - }} \right] = {{k\left[ {{H_2}S} \right]} \over {{H^ + }}}

Substituting this value in equation (1)(1) we find

Rate =k[Cl2]K[H2S]H+= k\left[ {C{l_2}} \right]K{{\left[ {{H_2}S} \right]} \over {{H^ + }}}

=k′[Cl2][H2S][H+]= k'{{\left[ {C{l_2}} \right]\left[ {{H_2}S} \right]} \over {\left[ {{H^ + }} \right]}}

hence only, mechanism (1)(1) is consistent with the given rate equation.

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