Question
Consider the decomposition of hydrogen peroxide in alkaline medium which is catalysed by iodide ions.
$\text{2H}_2\text{O}_2\xrightarrow{\text{OH}^-}2\text{H}_2\text{O}+\text{O}_2$
This reaction takes place in two step as given below:
Step-I $\text{H}_2\text{O}_2+\text{I}^-\rightarrow\text{H}_2\text{O}_2+\text{IO}^-\text{ (slow)}$
Step-II $\text{H}_2\text{O}_2+\text{IO}^-\rightarrow\text{H}_2\text{O}_2+\text{I}+\text{O}_2\text{ (fast})$
  1. Write the rate law expression and determine the order of reaction w.r.t. H2O2.
  2. What is the molecularity of each individual step?

Answer

  1. Rate = K[H2O2]1 [I-]1

Order of reaction w.r.t.H2O2 = 1.

  1. Molecularity of step I = 2 amd step II = 2.

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