Trichlorofluoromethane (CFCl3\text{CFCl}_3CFCl3) undergoes photolysis in the stratosphere, initiating a chain reaction that depletes the ozone layer. Which of the following statements correctly describes a feature of this depletion mechanism?
The photolytic initiation step involves the homolytic fission of the C−F\text{C}-\text{F}C−F bond rather than the C−Cl\text{C}-\text{Cl}C−Cl bond due to the higher electronegativity of fluorine.
In the propagation steps, the chlorine radical (Cl∙\text{Cl}^\bulletCl∙) acts as a reaction intermediate, whereas the chlorine monoxide radical (ClO∙\text{ClO}^\bulletClO∙) acts as the catalyst.
Chlorine radicals catalyze the overall decomposition of ozone (2O3→3O22\text{O}_3 \rightarrow 3\text{O}_22O3→3O2) by providing an alternative reaction pathway with a lower activation energy.
Hydrofluorocarbons (HFCs) are equally destructive to the ozone layer because stratospheric ultraviolet radiation easily breaks the C−H\text{C}-\text{H}C−H bonds to release reactive hydrogen radicals.
25 exam-style questions on AQA A Level Chemistry Halogenoalkanes, covering Nucleophilic substitution, Elimination, and Ozone depletion. Each one has a worked solution and a mark scheme showing where the marks go.