# Reaction Rate Question

Question
The rate of appearance of I2 in aqueous solution, in the reaction of the I- ion with hydrogen peroxide, was found to change from 3.7*10^-5 mol/dm^3 to 7.9*10^-5 mol/dm^3 over a time interval of 1.0 to 3.0s.
2H+(aq) + 2I-(aq) + H2O2(aq) --> I2(aq) + 2H2O(l)
a)What is the rate of appearance of H2 during this period?
b) At what rate should the concentration of the H+ ion be changing during this same time period?
c) Is this mechanism likely to occur in one step?

Attempt
a) rate(H2) = rate(I2)
rate(H2)=delta[H2]/delta t
rate(H2)=(7.9*10^-5 mol/dm^3-3.7*10^-5 mol/dm^3)/(3.0s-1.0s)
rate(H2)=2.1*10^-5 mol/(dm^3*s)
b)mol(H+)/mol(H2)=2/1 = 2
Therefore rate(H+)=2*(-2.1*10^-5 mol/(dm^3*s))
=-4.2*10^-5 mol/(dm^3*s)
c) No, it is not likely to occur in one step, as the overall reaction is not elementary: it has a molecularity of 5, and a molecularity of 3 or less must exist to ensure a one-step (elementary) mechanism.

I am unsure about the whole process. Please tell me if I did this correctly.