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Write Brief Answer · Q15

Q.On the basis of chemical reactions involved, explain how do CFC's cause depletion of ozone layer in stratosphere?

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Step 1. CFCs (Freons) are stable enough to survive the troposphere and slowly drift up into the stratosphere, where they persist for 50-100 years.

Step 2. In the presence of UV radiation there, CFCs break apart, releasing a chlorine free radical:

CF2Cl2→hνCF2Cl∙+Cl∙CF_2Cl_2 \xrightarrow{h\nu} CF_2Cl^{\bullet} + Cl^{\bullet}

CFCl3→hνCFCl2∙+Cl∙CFCl_3 \xrightarrow{h\nu} CFCl_2^{\bullet} + Cl^{\bullet}

Step 3. The chlorine radical attacks an ozone molecule, forming chlorine monoxide and molecular oxygen: Cl∙+O3→ClO∙+O2Cl^{\bullet} + O_3 \rightarrow ClO^{\bullet} + O_2.

Step 4. The chlorine monoxide then reacts with atomic oxygen, REGENERATING the chlorine radical: ClO∙+O→Cl∙+O2ClO^{\bullet} + O \rightarrow Cl^{\bullet} + O_2. …

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