What are chlorofluorocarbons (CFCs)?

Chlorofluorocarbons (CFCs) are compounds containing carbon, chlorine, and fluorine atoms.


They are halogenoalkanes in which all of the hydrogen atoms in the molecule have been replaced by chlorine and fluorine atoms.

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Explain the consequence of chlorofluorocarbons being released into the atmosphere.

UV light can break the C-Cl bonds in CFCs, releasing chlorine radicals that destroy ozone molecules in the stratosphere.

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Explain, with the use of equations, how chlorine free radicals (Cl•) catalyse the breakdown of ozone (O3) in the atmosphere.

  1. Breakdown of ozone by chlorine radicals:

Cl• + O3 ➔ ClO• + O2

  1. Regeneration of chlorine radicals:

ClO• + O3 ➔ 2O2 + Cl•

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What is the role of the ozone layer in Earth's atmosphere?

The ozone layer absorbs harmful ultraviolet radiation from the Sun, preventing it from reaching the Earth's surface.

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Why are CFCs so stable in the lower atmosphere?

CFCs are very stable in the lower atmosphere due to the strong carbon-halogen bonds within their molecules.


This stability allows CFCs to persist long enough to reach the upper atmosphere, where they break down when exposed to high energy UV radiation.

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How do CFCs produce chlorine radicals in the upper atmosphere?

In the upper atmosphere, high-energy UV radiation breaks the carbon-chlorine bonds in CFCs, causing the molecules to split apart. This initiation reaction releases highly reactive chlorine radicals (Cl•).


The equation for this initiation is: Cl2 ➔ Cl• + Cl•.

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Explain how one chlorine radical can catalyse the decomposition of many ozone molecules.

The chlorine radical starts a chain reaction that regenerates chlorine radicals while breaking down ozone. So each radical can repeatedly break down many ozone molecules.

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What are some alternatives to CFCs?

Hydrofluorocarbons (HFCs) and hydrocarbons.

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What is the overall equation for the breakdown of ozone (O3) in the atmosphere?

2O3 ➔ 3O2

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