Why does the rate equation between hydrogen peroxide and iodide ions not follow the stoichiometry of the rate-determining step?

The ionic equation of the reaction between hydrogen peroxide and iodide ions can be written as $\ce{H2O2 +2I- + 2H+ -> 2H2O +I2}$ which is the rate-determining step as well.

From what I have learnt, the order of reaction with respect to each reactant in the rate equation should be the coefficients of the respective reactants in the rate determining step.

So that makes the rate equation $= K\ce{[H2O2][I-]^2[H+]^2}$

However, from an experiment conducted, the rate equation I have obtained is rate $= k\ce{[H2O2][I-]}$ instead. Why is it so?

• It is extremely unlikely that the rate determining step involves 5 separate species... – Zhe Jun 8 '18 at 17:19