Answer to Question #154896 in General Chemistry for Lynil Ruth Caburnay

Question

If an average O3 molecule "lives" only 100-200 seconds in the stratosphere before undergoing dissociation, how can O3 offer any protection from ultraviolet radiation?

Answer 1

1. Step: the O₂ molecule is broken down by the absorption of a photon of radiant energy (l = 240 nm).
2. Step: diatomic oxygen molecules bond with single oxygen atoms to form ozone.
3. Step: O₃ absorbs a photon and is broken down into a diatomic oxygen molecule and an oxygen atom (occurs simultaneously to step 2) - Rate of O₃ formation = rate of O₃ destruction.
4. Step: ozone combines with a single oxygen atom to form 2 diatomic oxygen molecules an O₃ molecule lives 100-200 seconds before it is dissociated. The chapman cycle is not flawless; concentration levels of ozone are lower than those predicted from the simple chapman cycle. Although, the concentration of ozone in the stratosphere is very low, it is sufficient to filter out (absorb) solar radiation in the range of 200 - 300 nm.