How do halogenoalkanes cause depletion of the ozone layer?

Question 1

Common halogenoalkanes are chlorofluorocarbons (CFCs) which contain carbon, chlorine and fluorine atoms, e.g. CCl3F. They are…. properties and old uses

Answer 1

chemically inert and non-flammable and non-toxic. They have many uses due to their properties, e.g. as refrigerants, as propellants in aerosols and as solvents for dry cleaning

Question 2

Ozone, O, is formed naturally in the upper atmosphere. It is beneficial because it

Answer 2

3

absorbs ultraviolet radiation, preventing the majority of harmful UV radiation from reaching the Earth’s surface

Question 3

When CFCs reach the upper atmosphere, UV radiation……….

Answer 3

breaks the C–Cl bonds to form chlorine radicals, Cl*. Chlorine radicals catalyse the decomposition of ozone and contribute to the hole in the ozone layer:

Question 4

CFC’s ozone layer reaction

Answer 4

Propagation step 1: Cl* + O3 → ClO* + O2

Propagation step 2: ClO* + O3 → 2O2 + Cl*

Overall equation: 2O3 → 3O2

Question 5

Scientific research has provided sufficient evidence of the harmful effects of CFCs which has led to legislation to ban the use of CFCs as solvents as refrigerants. Chlorine-free alternatives, such as

Answer 5

such as HFCs, have been developed by chemists to replace CFCs.