Consider the following reaction: [S2O8]2- (aq) + 3[I]- (aq) ---> 2[SO4]2- (aq)+
ID: 76232 • Letter: C
Question
Consider the following reaction:[S2O8]2- (aq) + 3[I]- (aq) ---> 2[SO4]2- (aq)+ [I3]- (aq)
rate = k[S2O8]2-[I]-
When the reaction is followed under pseudo-first-order conditionswith [S2O8]2- = 200mM and [I]- = 1.5mM, the rate constant was1.82s-1. The second order rate constant, k, for the reaction is
A) 1.21*10^3 M-1*S-1
B) 6.07*10^3 M-1*S-1
C) 1.37*10^-2 M-1*S-1
D) 9.10 M-1*S-1
E) 1.82 M-1*S-1
Explanation / Answer
rate = k*[S2O82-][I-] Note that [S2O82-] = 200 mM >> 1.5 mM = [I-] So [S2O82-] is nearly constantthroughout the whole reaction rate = k*[S2O82-][I-] = k'[I-], where k' = k*[S2O82-] =1.82 s-1 Thus k = 1.82 s-1/[S2O82-] = 1.82s-1 / 200 mM *(1000 mM/1M) = 9.1 M-1*S-1, orD