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 $w.r.t. H_2O_2.$
  2. What is the molecularity of each individual step?

Answer

  1. Rate $= K[H_2O_2]^1 [I^-]^1$
  1. Order of reaction $w.r.t.H_2O_2 = 1.$
  2. Molecularity of step $I = 2$ amd step $II = 2.$

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