[djenko]

Hi, im a high school student doing a project on the iodine clock reaction. The particular reaction im looking at is also known as the "Harcourt-Essen" reaction. The reaction is thus:

H2O2(aq) + 2I-(aq) + 2H+(aq)  -->  I2(aq) + 2H2O(l)

Having carried out an experiment to find the order of this reaction with respect to [H+], i have worked this out to be 1/2 . Also, I've heard other people say that they have found the order with respect to [H+] to be other numbers. Can anyone tell me:
1. What kind of reaction mechanism could cause the order with respect to [H+] to be 1/2 ?
2. Why the order with respect to [H+] might be found different in separate experiments on the same reaction?

Thankyou