In recent years ozone in the stratosphere has been depleted at an alarmingly fast rate by chlorofluorocarbons (CFCs). A CFC molecule such as \(\mathrm{CFCl}_{3}\) is first decomposed by UV radiation: $$ \mathrm{CFCl}_{3} \longrightarrow \mathrm{CFCl}_{2}+\mathrm{Cl} $$ The chlorine radical then reacts with ozone as follows: $$ \begin{array}{c} \mathrm{Cl}+\mathrm{O}_{3} \longrightarrow \mathrm{ClO}+\mathrm{O}_{2} \\ \mathrm{ClO}+\mathrm{O} \longrightarrow \mathrm{Cl}+\mathrm{O}_{2} \end{array} $$ (a) Write the overall reaction for the last two steps. (b) What are the roles of \(\mathrm{Cl}\) and \(\mathrm{ClO} ?\) (c) Why is the fluorine radical not important in this mechanism? (d) One suggestion to reduce the concentration of chlorine radicals is to add hydrocarbons such as ethane \(\left(\mathrm{C}_{2} \mathrm{H}_{6}\right)\) to the stratosphere. How will this Work?

Step by step solution

01

Combine the reactions

To finalize the overall reaction for the last two steps, simply add the two reactions together and cancel out any terms that appear on both sides of the reaction equations: \(\mathrm{Cl} + \mathrm{O}_3 \longrightarrow \mathrm{ClO} + \mathrm{O}_2\) and \(\mathrm{ClO} + \mathrm{O} \longrightarrow \mathrm{Cl} + \mathrm{O}_2\). Adding these gives \(\mathrm{Cl} + \mathrm{O}_3 + \mathrm{O} \longrightarrow \mathrm{ClO} + \mathrm{O}_2 + \mathrm{Cl} + \mathrm{O}_2\). Canceling out the \(\mathrm{Cl}\) on both sides and the \(\mathrm{O}_2\) on the right gives \(\mathrm{O}_3 + \mathrm{O} \longrightarrow 2 \mathrm{O}_2\).

02

Roles of \(\mathrm{Cl}\) and \(\mathrm{ClO}\)

\(\mathrm{Cl}\) acts as a catalyst in this sequence of reactions. It is used in the first reaction, and regenerated in the second, allowing it to participate again in the first reaction. \(\mathrm{ClO}\), on the other hand, is an intermediate. It is formed in the first reaction and used up in the second.

03

The role of fluorine

The fluorine radical is not important in this mechanism because it does not react readily with ozone. This is due to its low reactivity compared to chlorine.

04

The effect of adding hydrocarbons

Adding hydrocarbons such as ethane could reduce the concentration of chlorine radicals, as these hydrocarbons would react readily with chlorine, forming less reactive compounds and consuming the chlorine radicals in the process.

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