Chapter 18, Problem 100A

(a)

Interpretation Introduction

Interpretation: The intermediate is to be identified.

Concept Introduction: The rate is a method for determining how much something changes over a predetermined period of time. The amount of reactant or product that changes per unit of time is the reaction rate.

Answer to Problem 100A

The intermediate formed is ${\text{IO}}^{-}$ .

Explanation of Solution

The mechanism for the decomposition of hydrogen peroxide is given as follows:

  $\begin{array}{l}{\text{H}}_{\text{2}}{\text{O}}_{\text{2}}\left(aq\right)+{\text{I}}^{-}\left(aq\right) \to {\text{H}}_{\text{2}}\text{O}\left(l\right)+{\text{IO}}^{-}\left(aq\right)\left(slow\right)\hfill \\ {\text{IO}}^{-}\left(aq\right)+{\text{H}}_{\text{2}}{\text{O}}_{\text{2}}\left(aq\right) \to {\text{H}}_{\text{2}}\text{O}\left(l\right)+{\text{O}}_{\text{2}}\left(g\right)+{\text{I}}^{-}\left(aq\right)\left(fast\right)\hfill \end{array}$

The term "activated complex" refers to the state of the particles that are situated between reactants and products.

A temporary atomic configuration at the top of the activation energy barrier is known as an activated complex.

The intermediate formed is ${\text{IO}}^{-}$ .

(b)

Interpretation Introduction

Interpretation: The minimum number of activated complexes is to be described.

Concept Introduction: The rate is a method for determining how much something changes over a predetermined period of time. The amount of reactant or product that changes per unit of time is the reaction rate.

Answer to Problem 100A

The minimum number of activated complexes is two.

Explanation of Solution

The mechanism for the decomposition of hydrogen peroxide is given as follows:

  $\begin{array}{l}{\text{H}}_{\text{2}}{\text{O}}_{\text{2}}\left(aq\right)+{\text{I}}^{-}\left(aq\right) \to {\text{H}}_{\text{2}}\text{O}\left(l\right)+{\text{IO}}^{-}\left(aq\right)\left(slow\right)\hfill \\ {\text{IO}}^{-}\left(aq\right)+{\text{H}}_{\text{2}}{\text{O}}_{\text{2}}\left(aq\right) \to {\text{H}}_{\text{2}}\text{O}\left(l\right)+{\text{O}}_{\text{2}}\left(g\right)+{\text{I}}^{-}\left(aq\right)\left(fast\right)\hfill \end{array}$

In stepwise chemical processes with numerous elementary steps, an intermediate is a molecular entity that is created from the reactants (or previous intermediates) but consumed in subsequent reactions.

The minimum number of activated complexes needed to explain the reaction is two.

(c)

Interpretation Introduction

Interpretation: The two reactions that has the smaller specific rate constant is to be identified.

Concept Introduction: The rate is a method for determining how much something changes over a predetermined period of time. The amount of reactant or product that changes per unit of time is the reaction rate.

Answer to Problem 100A

The slow reaction will have smaller specific rate constant.

Explanation of Solution

The mechanism for the decomposition of hydrogen peroxide is given as follows:

  $\begin{array}{l}{\text{H}}_{\text{2}}{\text{O}}_{\text{2}}\left(aq\right)+{\text{I}}^{-}\left(aq\right) \to {\text{H}}_{\text{2}}\text{O}\left(l\right)+{\text{IO}}^{-}\left(aq\right)\left(slow\right)\hfill \\ {\text{IO}}^{-}\left(aq\right)+{\text{H}}_{\text{2}}{\text{O}}_{\text{2}}\left(aq\right) \to {\text{H}}_{\text{2}}\text{O}\left(l\right)+{\text{O}}_{\text{2}}\left(g\right)+{\text{I}}^{-}\left(aq\right)\left(fast\right)\hfill \end{array}$

The reaction that has the smaller specific rate constant is the reaction that takes place slowly.

The reaction with small specific rate constant is as follows:

  ${\text{H}}_{\text{2}}{\text{O}}_{\text{2}}\left(aq\right)+{\text{I}}^{-}\left(aq\right) \to {\text{H}}_{\text{2}}\text{O}\left(l\right)+{\text{IO}}^{-}\left(aq\right)\left(slow\right)$

(d)

Interpretation Introduction

Interpretation: The overall balanced chemical equation for the reaction is to be written.

Concept Introduction: The rate is a method for determining how much something changes over a predetermined period of time. The amount of reactant or product that changes per unit of time is the reaction rate.

Answer to Problem 100A

The overall chemical equation is as follows:

  ${\text{2H}}_{\text{2}}{\text{O}}_{\text{2}}\left(aq\right) \to 2{\text{H}}_{\text{2}}\text{O}\left(l\right)+{\text{O}}_{\text{2}}\left(g\right)$

Explanation of Solution

The mechanism for the decomposition of hydrogen peroxide is given as follows:

  $\begin{array}{l}{\text{H}}_{\text{2}}{\text{O}}_{\text{2}}\left(aq\right)+{\text{I}}^{-}\left(aq\right) \to {\text{H}}_{\text{2}}\text{O}\left(l\right)+{\text{IO}}^{-}\left(aq\right)\left(slow\right)\hfill \\ {\text{IO}}^{-}\left(aq\right)+{\text{H}}_{\text{2}}{\text{O}}_{\text{2}}\left(aq\right) \to {\text{H}}_{\text{2}}\text{O}\left(l\right)+{\text{O}}_{\text{2}}\left(g\right)+{\text{I}}^{-}\left(aq\right)\left(fast\right)\hfill \end{array}$

On combining the above two equations, the overall chemical equation is written.

The overall chemical equation is as follows:

  ${\text{2H}}_{\text{2}}{\text{O}}_{\text{2}}\left(aq\right) \to 2{\text{H}}_{\text{2}}\text{O}\left(l\right)+{\text{O}}_{\text{2}}\left(g\right)$

(e)

Interpretation Introduction

Interpretation: ${\text{I}}^{-}$ as catalyst is to be explained.

Concept Introduction: The rate is a method for determining how much something changes over a predetermined period of time. The amount of reactant or product that changes per unit of time is the reaction rate.

Answer to Problem 100A

  ${\text{I}}^{-}$ does not qualify as a catalyst.

Explanation of Solution

The mechanism for the decomposition of hydrogen peroxide is given as follows:

  $\begin{array}{l}{\text{H}}_{\text{2}}{\text{O}}_{\text{2}}\left(aq\right)+{\text{I}}^{-}\left(aq\right) \to {\text{H}}_{\text{2}}\text{O}\left(l\right)+{\text{IO}}^{-}\left(aq\right)\left(slow\right)\hfill \\ {\text{IO}}^{-}\left(aq\right)+{\text{H}}_{\text{2}}{\text{O}}_{\text{2}}\left(aq\right) \to {\text{H}}_{\text{2}}\text{O}\left(l\right)+{\text{O}}_{\text{2}}\left(g\right)+{\text{I}}^{-}\left(aq\right)\left(fast\right)\hfill \end{array}$

A catalyst is a chemical that can be included in a reaction to speed up the process without being consumed.

Typically, catalysts shorten the activation energy of a process or alter its mechanism.

  ${\text{I}}^{-}$ is not a catalyst as it is involved in the reaction as a reactant.

The catalyst can not be a reactant, product or intermediate.