What does strong UV (lambda < 220 nm) do to a CFC such as CCl2F2 in the stratosphere?

Breaks the C-Cl bond, releasing a chlorine atom (Cl.)

Breaks the C-F bond releasing fluorine atoms

Does nothing, since CFCs absorb no UV

What is the chain reaction of chlorine with ozone?

Cl. + O3 -> ClO. + O2, then ClO. + O -> Cl. + O2

Cl. + O2 -> ClO2, then ClO2 -> Cl. + O2

Cl. + O3 -> ClO3 which is stable

What is the net reaction and role of Cl?

O3 + O -> 2O2; Cl is regenerated (catalyst)

Why does net ozone decrease?

Chlorine adds an extra catalytic destruction cycle to the normal formation-destruction balance

UV no longer reaches the stratosphere

2068 Bhadra · 2 marks

Photochemistry behind ozone layer depletion

Short answer

CFCs photolyse under UV, releasing chlorine atoms. Chlorine catalytically destroys ozone: Cl + O3 -> ClO + O2; ClO + O -> Cl + O2, net O3 + O -> 2O2. One Cl atom can destroy about 10^5 ozone molecules before removal, depleting the layer.

What is the photochemistry behind ozone layer depletion?

Because CFCs are so stable, they slowly rise to the stratosphere, where strong UV radiation (λ < 220 nm) breaks the C–Cl bond and releases chlorine atoms:

CCl₃F  + hν → •CCl₂F + Cl•
CCl₂F₂ + hν → •CClF₂ + Cl•

The free chlorine atom then destroys ozone in a chain reaction:

Cl• + O₃  → ClO• + O₂
ClO• + O  → Cl• + O₂
-------------------------------
Net:  O₃ + O → 2O₂        (Cl• is regenerated)

A single Cl atom can destroy about 10⁵ ozone molecules before it is removed (for example, as HCl by reaction with CH₄, or as ClONO₂ when ClO combines with NO₂).

Ozone is normally formed and destroyed in balance: O₂ + hν → 2O; O + O₂ → O₃; O₃ + hν → O₂ + O. The chlorine released from CFCs adds an extra, catalytic destruction cycle, so net ozone decreases.

✓ Answer checked by Claude Opus 5.5 (high effort)

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