AP chemistry的一道题目

题目

AP chemistry的一道题目
Step 1:N2H2O2  N2HO2- + H+ (fast equilibrium)
Step 2:N2HO2-  N2O + OH- (slow)
Step 3:H+ + OH-  H2O (fast)
Nitramide,N2H2O2,decomposes slowly in aqueous solution.This decomposition is believed to occur according to the reaction mechanism above.The rate law for the decomposition of nitramide that is consistent with this mechanism is given by which of the following?
(A) Rate= k[N2H2O2]
(B) Rate= k[N2H2O2][H+]
(C) Rate= k[N2H2O2]/[H+]
(D) Rate= k[N2H2O2]/[N2HO2-]
(E) Rate= k[N2H2O2][OH-]
Answer:C
请具体讲一讲为什么选C啊?

答案

The rate law is determined in this case by the slowest reaction step:
rate = k[N2HO2-]
Equilibrium for step before the slowest step:
K = [N2HO2-][H+] / [N2H2O2]
K[N2H2O2] / [H+] = [N2HO2-]
rate = k{K[N2H2O2] / [H+]}
rate = (k1)[N2H2O2] / [H+]