Chapter 21, Problem 21.63QP

 (a)

Interpretation Introduction

Interpretation: The given conditions for the process of formation of OH free radical the reason for the low concentration of OH in the troposphere (a), the property which makes OH a strong oxidizing agent (b) the reaction equation for the reaction between OH and ${\text{NO}}_{\text{2}}$(c) and the balanced chemical reaction equation for the oxidation reaction of ${\text{SO}}_{\text{2}}$ to ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ by OH radical (d) should be determined.

Concept Introduction:

• Free radicals are the reaction intermediate that contain at least one unpaired electron.
• Troposphere is the lowest region of the atmosphere, extending from the earth's surface to a height of about 6–10 km .
• Concentration is a quantitative measure of the number of atoms per unit volume in a sample of a matter. The matter might be in the solid, liquid, or gaseous state.
• Reactivity is the impetus for which a chemical reaction undergoes a chemical reaction. Small concentration of substance in a reaction is the results of its high reactivity.
• Oxidizing agent are the substances that being reduced to bring a chemical reaction by gaining electrons. Free radicals are always good oxidizing agent.
• Reaction equation is the symbolic representation of a chemical reaction in which the reactants are placed on the left hand side and the product formed in the reaction is placed on the right hand side.
• Balanced chemical equation of a reaction is written according to law of conservation of mass
• To find: the reason for the small concentration of OH radical in the troposphere.

Answer to Problem 21.63QP

Its small concentration is the result of the high reactivity of the OH radical

Explanation of Solution

Troposphere is the lowest region of the atmosphere, extending from the earth's surface to a height of about 6–10 k. In troposphere region of atmosphere free radicals especially hydroxyl free radical (OH) is present in trace amount.

Free radicals are the reaction intermediate that contain at least one unpaired electron. The hydroxyl free radical (OH) is formed by the following reaction,

               $\begin{array}{l}{\text{O}}_{\text{3}}\stackrel{\text{λ=320}\text{nm}}{\to }{\text{O}}^{\text{*}}\text{+}{\text{O}}_{\text{2}}\\ \text{O}\text{+}{\text{H}}_{\text{2}}\text{O}\to \text{2OH}\end{array}$

Where ${\text{O}}^{\text{*}}$ denotes an electrically excited atom.

The concentration of hydroxyl free radicals produced by this reaction is so small even though the concentration of ${\text{O}}_{\text{3}}$ and ${\text{H}}_{\text{2}}\text{O}$ are quite large in the troposphere. Its small concentration is the result of the high reactivity of the OH radical.

Reactivity is the impetus for which a chemical reaction undergoes a chemical reaction.

(b)

Interpretation Introduction

Interpretation: The given conditions for the process of formation of OH free radical the reason for the low concentration of OH in the troposphere (a), the property which makes OH a strong oxidizing agent (b) the reaction equation for the reaction between OH and ${\text{NO}}_{\text{2}}$(c) and the balanced chemical reaction equation for the oxidation reaction of ${\text{SO}}_{\text{2}}$ to ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ by OH radical (d) should be determined.

Concept Introduction:

• Free radicals are the reaction intermediate that contain at least one unpaired electron.
• Troposphere is the lowest region of the atmosphere, extending from the earth's surface to a height of about 6–10 km .
• Concentration is a quantitative measure of the number of atoms per unit volume in a sample of a matter. The matter might be in the solid, liquid, or gaseous state.
• Reactivity is the impetus for which a chemical reaction undergoes a chemical reaction. Small concentration of substance in a reaction is the results of its high reactivity.
• Oxidizing agent are the substances that being reduced to bring a chemical reaction by gaining electrons. Free radicals are always good oxidizing agent.
• Reaction equation is the symbolic representation of a chemical reaction in which the reactants are placed on the left hand side and the product formed in the reaction is placed on the right hand side.
• Balanced chemical equation of a reaction is written according to law of conservation of mass

Answer to Problem 21.63QP

1. (a) Its small concentration is the result of the high reactivity of the OH radical
2. (b) OH has an unpaired electron; free radicals are always good oxidizing agent.
3. (c) The reaction equation for the reaction between $\text{OH}\text{}$ and  ${\text{NO}}_{\text{2}}$ is, 

   $\text{OH}\text{+}{\text{NO}}_{\text{2}}\to {\text{HNO}}_{\text{3}}$

4. (d) The hydroxyl free radical can oxidize ${\text{SO}}_{\text{2}}$ to ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$  the reaction equation for this is,

   $\begin{array}{l}\text{OH}\text{+}\text{}{\text{SO}}_{\text{2}}\to {\text{HSO}}_{\text{3}}\\ {\text{HSO}}_{\text{3}}\text{+}{\text{O}}_{\text{2}}\text{+}{\text{H}}_{\text{2}}\text{O}\to {\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}\text{+}{\text{HO}}_{\text{2}}\end{array}$

To find: the property behind the strength of oxidizing power of OH radical.

Explanation of Solution

Free radicals are the reaction intermediate that contain at least one unpaired electron. The hydroxyl free radical (OH) is formed by the following reaction,

               $\begin{array}{l}{\text{O}}_{\text{3}}\stackrel{\text{λ=320}\text{nm}}{\to }{\text{O}}^{\text{*}}\text{+}{\text{O}}_{\text{2}}\\ \text{O}\text{+}{\text{H}}_{\text{2}}\text{O}\to \text{2OH}\end{array}$

Where ${\text{O}}^{\text{*}}$ denotes an electrically excited atom

Here the hydroxyl radical (OH) has an unpaired electron it can accept a pair of electron then it can bring a chemical reaction by being reduced by itself. This type of chemical process is known as oxidation reaction.

Therefore hydroxyl free radical acts as good oxidizing agents because it has an unpaired electron.

(c)

Interpretation Introduction

Interpretation: The given conditions for the process of formation of OH free radical the reason for the low concentration of OH in the troposphere (a), the property which makes OH a strong oxidizing agent (b) the reaction equation for the reaction between OH and ${\text{NO}}_{\text{2}}$(c) and the balanced chemical reaction equation for the oxidation reaction of ${\text{SO}}_{\text{2}}$ to ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ by OH radical (d) should be determined.

Concept Introduction:

• Free radicals are the reaction intermediate that contain at least one unpaired electron.
• Troposphere is the lowest region of the atmosphere, extending from the earth's surface to a height of about 6–10 km .
• Concentration is a quantitative measure of the number of atoms per unit volume in a sample of a matter. The matter might be in the solid, liquid, or gaseous state.
• Reactivity is the impetus for which a chemical reaction undergoes a chemical reaction. Small concentration of substance in a reaction is the results of its high reactivity.
• Oxidizing agent are the substances that being reduced to bring a chemical reaction by gaining electrons. Free radicals are always good oxidizing agent.
• Reaction equation is the symbolic representation of a chemical reaction in which the reactants are placed on the left hand side and the product formed in the reaction is placed on the right hand side.
• Balanced chemical equation of a reaction is written according to law of conservation of mass
• To write: the balanced chemical reaction equation for the oxidation reaction of ${\text{SO}}_{\text{2}}$ to ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ by OH radical
• To write: the balanced chemical reaction equation for the reaction between $\text{OH}\text{}$ and ${\text{NO}}_{\text{2}}$.

Answer to Problem 21.63QP

The reaction equation for the reaction between $\text{OH}\text{}$ and  ${\text{NO}}_{\text{2}}$ is,

$\text{OH}\text{+}{\text{NO}}_{\text{2}}\to {\text{HNO}}_{\text{3}}$

Explanation of Solution

In the given reaction, hydroxyl free radical is reacting with sulfur dioxide hydroxide leads to the formation of hydrogen sulfite.

Therefore,

The chemical equation for this reaction is,

                  ${\text{OH+SO}}_{\text{2}}\to {\text{HSO}}_{\text{3}}$

Balanced chemical equation of a reaction is written according to law of conservation of mass.

Therefore,

The total number of each atoms in the reactant side should equal to the total number of each atoms in the product side.

So, in order to balance a chemical equation, the coefficients of compounds or atoms are needed to be changed in such a way that total number of each atoms in the reactant side and the total number of each atoms in the product side is to become equal.

Hence,

The above chemical equation is a balanced chemical equation.

Therefore,

The balanced equations for the given reaction is

        ${\text{OH+SO}}_{\text{2}}\to {\text{HSO}}_{\text{3}}$

(d)

Interpretation Introduction

Interpretation: The given conditions for the process of formation of OH free radical the reason for the low concentration of OH in the troposphere (a), the property which makes OH a strong oxidizing agent (b) the reaction equation for the reaction between OH and ${\text{NO}}_{\text{2}}$(c) and the balanced chemical reaction equation for the oxidation reaction of ${\text{SO}}_{\text{2}}$ to ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$ by OH radical (d) should be determined.

Concept Introduction:

• Free radicals are the reaction intermediate that contain at least one unpaired electron.
• Troposphere is the lowest region of the atmosphere, extending from the earth's surface to a height of about 6–10 km .
• Concentration is a quantitative measure of the number of atoms per unit volume in a sample of a matter. The matter might be in the solid, liquid, or gaseous state.
• Reactivity is the impetus for which a chemical reaction undergoes a chemical reaction. Small concentration of substance in a reaction is the results of its high reactivity.
• Oxidizing agent are the substances that being reduced to bring a chemical reaction by gaining electrons. Free radicals are always good oxidizing agent.
• Reaction equation is the symbolic representation of a chemical reaction in which the reactants are placed on the left hand side and the product formed in the reaction is placed on the right hand side.
• Balanced chemical equation of a reaction is written according to law of conservation of mass

Answer to Problem 21.63QP

The hydroxyl free radical can oxidize ${\text{SO}}_{\text{2}}$ to ${\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}$  the reaction equation for this is,

$\begin{array}{l}\text{OH}\text{+}\text{}{\text{SO}}_{\text{2}}\to {\text{HSO}}_{\text{3}}\\ {\text{HSO}}_{\text{3}}\text{+}{\text{O}}_{\text{2}}\text{+}{\text{H}}_{\text{2}}\text{O}\to {\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}\text{+}{\text{HO}}_{\text{2}}\end{array}$

Explanation of Solution

Explanation   

In the given reaction, hydroxyl free radical is reacting with sulfur dioxide hydroxide leads to the formation of hydrogen sulfite. And the hydrogen sulfite reacts with oxygen and water in the troposphere to form sulfuric acid and hydroxyl free radical.

Therefore,

The chemical equation for this reaction is,

                      ${\text{OH+SO}}_{\text{2}}\to {\text{HSO}}_{\text{3}}$

                           ${\text{HSO}}_{\text{3}}{\text{+O}}_{\text{2}}{\text{+H}}_{\text{2}}\text{O}\to {\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}\text{+}{\text{HO}}_{\text{2}}$

Balanced chemical equation of a reaction is written according to law of conservation of mass.

Therefore,

The total number of each atom in the reactant side should equal to the total number of each atoms in the product side.

So, in order to balance a chemical equation, the coefficients of compounds or atoms are needed to be changed in such a way that total number of each atoms in the reactant side and the total number of each atoms in the product side is to become equal.

Hence,

The above chemical equation is a balanced chemical equation.

Therefore,

The balanced equations for the given reaction is

           ${\text{OH+SO}}_{\text{2}}\to {\text{HSO}}_{\text{3}}$

${\text{HSO}}_{\text{3}}{\text{+O}}_{\text{2}}{\text{+H}}_{\text{2}}\text{O}\to {\text{H}}_{\text{2}}{\text{SO}}_{\text{4}}\text{+}{\text{HO}}_{\text{2}}$