5Br-(aq) + BrO3-(aq) + 6H+(aq) --> 3Br2(l) + 3H2O(l ) The above reaction is expe

Question

5Br-(aq) + BrO3-(aq) + 6H+(aq) --> 3Br2(l) + 3H2O(l)

The above reaction is expected to obey the mechanism:

BrO3-(aq) + H+(aq) = HBrO3(aq) Fast equilibrium

HBrO3(aq) + H+(aq) = H2BrO3+(aq) Fast equilibrium

H2BrO3+(aq) + Br-(aq) --> (Br-BrO2)(aq) + H2O(l) Slow

(Br-BrO2)(aq) + 4H+(aq) + 4Br-(aq) --> products Fast

Choose, from the list below, correct expressions for the overall rate law which are completely consistent with the above mechanism.

A. -d[BrO3-]/dt = k[Br-][BrO3-]2[H+]

B. -d[BrO3-]/dt = k[Br-][BrO3-][H+]2

C. -d[H+]/dt = k[BrO3-][Br-][H+]2

D. -d[Br-]/dt = k[Br-]2[BrO3-][H+]

E. -d[Br-]/dt = k[H+]2[Br-][BrO3-]

F. k[H+][Br-][BrO3-]2 = -d[BrO3-]/dt

For each of the given rate expressions choose the correct expression for the rate constant (k) from the list below.

A. k = 6(k(1)-k(-1))(k(2)-k(-2))k(3)

B. k = k(1)-k(-1)

C. k = k(1)k(2)k(3)/k(-1)k(-2)

D. k = 6(k(1)k(2)k(3)/k(-1)k(-2))

E. k = 5(k(1)+k(2)+k(3))/(k(-1)+k(-2))

F. none of the above

-d[BrO3-]/dt A B C D E F

-d[Br-]/dt A B C D E F

-d[H+]/dt A B C D E F

Explanation / Answer

For the first question, the reaction obeys slow mechanism
H2BrO3+(aq) + Br-(aq) --> (Br-BrO2)(aq) + H2O(l) ----- Slow

BrO3-+ H+ -----------> HBrO3
HBrO3 + H+ ------------> H2BrO3+
H2BrO3+ + Br------------> (Br-BrO2) + H2O
--------------------------------------------------
Br- + BrO3- + 2H+ -------------> (Br-BrO2)+ H2O
From the above overall equation write an rate expression which is option B

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