The decomposition of hydrogen peroxide is catalyzed by...

The decomposition of hydrogen peroxide is catalyzed by iodide ion. The catalyzed reaction is thought to proceed by a two-step mechanism: $$ \begin{array}{c}{\mathrm{H}_{2} \mathrm{O}_{2}(a q)+\mathrm{I}^{-}(a q) \longrightarrow \mathrm{H}_{2} \mathrm{O}(l)+\mathrm{IO}^{-}(a q) \text { (slow) }} \\ {\mathrm{IO}^{-}(a q)+\mathrm{H}_{2} \mathrm{O}_{2}(a q) \longrightarrow \mathrm{H}_{2} \mathrm{O}(l)+\mathrm{O}_{2}(\mathrm{g})+\mathrm{I}^{-}(a q) \text { (fast) }}\end{array} $$ $\begin{array}{l}{\text { (a) Write the chemical equation for the overall process. }} \\ {\text { (b) Identify the intermediate, if any, in the mechanism. }} \\ {\text { (c) Assuming that the first step of the mechanism is rate }} \\ {\text { determining, predict the rate law for the overall process. }}\end{array}$

Key Concepts

Reaction Mechanism

A reaction mechanism describes the step?by?step process by which reactants are converted into products. It involves multiple elementary steps that, when combined, provide the overall reaction. Understanding a mechanism allows chemists to deduce how catalysts work, identify intermediates, and predict reaction kinetics.

Intermediate

An intermediate is a transient species formed in one step of a reaction mechanism that is consumed in a subsequent step. Intermediates do not appear in the overall balanced equation because they are produced and then used up during the reaction process.

Rate-Determining Step

The rate-determining step is the slowest step in a reaction mechanism and thus controls the overall rate of the reaction. Because of its slow nature, the kinetics of this step typically dictates the form of the rate law for the entire reaction.

Rate Law

The rate law expresses the relationship between the reaction rate and the concentrations of the reactants, often derived from the rate-determining step if it is significantly slower than the other steps. This derivation provides insight into the kinetic order of each reactant.

Overall Reaction Equation

The overall reaction equation is obtained by summing the elementary steps of the mechanism and canceling out any species that appear on both sides of the equation. It provides the global stoichiometry of the reactants and products without showing intermediate species.

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