Page 210 - Chemistry ICSE Class IX

198 ICSE Chemistry – 9

Excessive use of chlorofluorocarbons
The major cause for the destruction of the ozone layer is the release of
chloro uorocarbons (CFCs) called freons into the atmosphere. CFCs are
used in aerosol sprays, as solvent, as refrigerants and as blowing agents for
plastic foams, such as Thermocol and Styrofoam. Chloro uorocarbons are
chemically nonreactive, nontoxic and odourless compounds. Some typical
chloro uorocarbons are
Š CF Cl (CFC-12) Dichlorodi uoromethane
2
2
Š CFCl (CFC-11) Trichloro uoromethane
3
When CFCs enter the atmosphere, they get decomposed by the action
of ultraviolet (UV) radiation coming from the sun.

CF Cl (g) + hv o Cl (g) + CClF 2
2
2
ultraviolet chlorine radical
radiation (highly reactive)

The Cl produced then reacts with ozone to permit the following
chain reaction:

Cl (g) + O (g) o ClO(g) + O (g)
3
2
Ozone

ClO(g) + O(g) o Cl (g) + O (g)
2
chlorine monoxide atomic chlorine
radical oxygen radical

The regenerated radical ( Cl) reacts with more ozone and the chain
thus continues.
Burning of aviation fuel
During the burning of aviation fuel in aeroplanes; oxides of carbon, oxides
of nitrogen and hydroxyl free radicals are formed. The nitric oxide (NO)

and hydroxyl radical ( OH) destroy ozone as follows:
O (g) + NO(g) o O (g) + NO (g)
2
2
3
ozone nitrogen dioxide
O (g) + O(g) o 2O (g)
2
3

O (g) + OH(g) o O (g) + HOO (g)
3
2

HOO (g) + O(g) o HO (g) + O 2
How can the destruction of ozone be minimised
Destruction of ozone can be minimised by reducing the production
and use of chloro uorohydrocarbons (CFCs) and replacing these by
hydro uorocarbons (HFCs).
ASSIGNMENT 6

Ozone depletion, Formation and function of ozone layer,
Destruction of ozone-Ozone hole, Chemicals responsible for ozone destruction

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ϱ͘ EĂŵĞ ƚǁŽ ĐŚĞŵŝĐĂůƐ ƌĞƐƉŽŶƐŝďůĞ ĨŽƌ ƚŚĞ ŽnjŽŶĞ ĚĞƐƚƌƵĐƟŽŶ͘
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