Question
For a reaction
\[\ce{2H2O2->[I^-][Alkaline medium]2H2O + O2}\]
The Proposed mechanism is given below:
(1) H2O2+I- → H2O+IO-(slow)
(2) H2O2+IO-→H2O+I-+O2(fast)
(i) Write the rate law for the reaction.
(ii) Write the overall order of a reaction.
(iii) Out of steps(1) and (2), which one is the rate-determining step?
Solution
Let us consider the problem:
\[\ce{2H2O2->[I^-][Alkaline medium]2H2O + O2}\]
In Some cases, the rate of reaction depends not only on the reactant but may also depend on the substance present as a catalyst. This is also seen in the above reaction. The rate of reaction depends on the slowest step in case of a complex reaction.
(1) \[\ce{H2O + I^- ->[slow]H2O + IO^- }\]
(2) \[\ce{H2O2 + IO^- ->[fast]H2O + I^- + O2}\]
(i) Rate law:
Rate =`-1/2("d"["H"_2"O"_2])/"dt"="k"["H"_2"O"_2]["I"^-]`
(ii) The overall order of reaction:
Rate = k[[H2O2] `["I"^-]`
Order = 1 + 1 = 2
(iii) Slowest step is the rate determining step. Hence, step 1 is rate determining step.
