Chapter 14: Problem 136
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: $$ \begin{array}{l} \mathrm{Cl}+\mathrm{O}_{3} \longrightarrow \mathrm{ClO}+\mathrm{O}_{2} \\ \mathrm{ClO}+\mathrm{O} \longrightarrow \mathrm{Cl}+\mathrm{O}_{2} \end{array} $$ (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? (e) Draw potential-energy versus reaction progress diagrams for the uncatalyzed and catalyzed (by Cl) destruction of ozone: \(\mathrm{O}_{3}+\mathrm{O} \longrightarrow 2 \mathrm{O}_{2} .\) Use the thermodynamic data in Appendix 2 to determine whether the reaction is exothermic or endothermic.
Short Answer
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Key Concepts
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