Explain the rate determining step with an example.

Explanation

(i) Let us consider reaction, the decomposition of hydrogen peroxide catalysed by `I^(-)`.
`2H_(2)O_(2(aq))rarr 2H_(2)O_((l))+O_(2(g))`
(ii) It is experimentally found that the reaction is first order with respect to both `H_(2)O_(2)` and `I^(-)`, which indicates that `I^(-)` is also involved in the reaction. The mechanism involves the following steps.
Step : 1
`H_(2)O_(2(aq))+I_((aq))^(-)rarr H_(2)O_((l))+OI_((aq))^(-)`
Step : 2
`H_(2)O_(2(aq))+OI_((aq))^(-)rarr H_(2)O_((l))+I_((aq))^(-)+O_(2(g))`
Overall reaction is
`2H_(2)O_(2(aq))rarr 2H_(2)O_((l))+O_(2(g))`
(iii) Thesetwo reactions are elementary reactions. Adding equ (1) and (2) gives the overall reaction. Step 1 is the rate determining step, since it involves both `H_(2)O_(2)` and `I^(-)`, the overall reaction is bimolecular.