Question

Write the uses of freon. What is its impact on the environment?

Hint:

Freons are CFCs such as CCl₂F₂, used as refrigerants and propellants; in the stratosphere they release Cl radicals that deplete the ozone layer.

Answer 1

Step 1: Identity. 'Freon' is the trade name for chlorofluorocarbons (CFCs). Typical members are Freon-12 (CCl₂F₂) and Freon-11 (CCl₃F). They are colourless, non-toxic, non-flammable and chemically inert.
Step 2: Where they are used. Because they are non-toxic and easily liquefiable, freons are used as cooling fluids (refrigerants) in fridges and ACs, as spray propellants in aerosol cans, and as foaming and cleaning agents in industry.
Step 3: Journey to the stratosphere. Their inertness is exactly the problem: they are not destroyed in the lower atmosphere and drift up to the ozone layer.
Step 4: Radical chain that destroys ozone. UV light splits the weak C-Cl bond to give a chlorine atom (radical), which turns ozone into oxygen and is then set free again to repeat the cycle:
\[CCl_2F_2 \xrightarrow{h\nu} Cl^{\bullet} + CClF_2^{\bullet}\]
\[Cl^{\bullet} + O_3 \rightarrow ClO^{\bullet} + O_2, \qquad ClO^{\bullet} + O \rightarrow Cl^{\bullet} + O_2\]
Step 5: Damage caused. Thinning of the ozone layer increases UV-B at ground level, raising the risk of skin cancer and cataracts in humans and lowering crop yields. This is why CFCs are being replaced by safer alternatives under the Montreal Protocol.