1) In order to destroy ozone in the upper stratosphere, why is the mechanism inv

Question

1) In order to destroy ozone in the upper stratosphere, why is the mechanism involving dichloroperoxide of negligible importance compared to the one that proceeds by ClO + O?

2) Reactions of the type OH + CF2Cl2 --> HOF + ·CFCl2are conceivable tropospheric sinks for CFCs. Can you deduce why they do not occur, given that C-F bonds are much stronger than O-F bonds

3) For the compounds CFCl3, CHFCl2, CF3Cl and CHF3, Assuming that equal numbers of moles of each were released into the air at ground level, rank these four compounds in terms of their potential to catalytically destroy ozone in the stratosphere and explain why this is the case.   

Explanation / Answer

1) In upper atmosphere the concentration of O is high. It reacts with ClO, and keeps the concentration of ClO very low. For dimeriation reaction the concentration of ClO must be very high because the rate of reaction is second order with respect to ClO.
2) Yes, it is difficult to break C-F bonds ans they are very strong bonds so the reaction is not feasible.

3) The destruction of ozone is done due to

CFCl3 + UV Light ==> CFCl2 + Cl
Cl + O3 ==> ClO + O2

so more the free Cl atoms more the destruction

each mole of CFCl3 will give three moles of Cl while CHFCl2 will give two and CFCl will give one while CHF3 will not give Cl atoms

So the increaseing order of thier potenital to destroy ozone will be

CHF3 < CF3Cl < CHFCl2 < CFFl3

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