CHEMISTRY 253
Spring, 2015 - Dixon
Group Assignment #3
Open Book – But 30 min. time limit
Group Names _________________________________________________
1. Ozone in the stratosphere is catalytically destroyed by Mechanism I and Mechanism II with X being Cl, Br, NO or OH.
If one is only looking at one X species (e.g. only Cl), the Mechanism I and Mechanism II reactions only lead to O3 loss. However, if we are looking at two different species (e.g. X = Cl and X’ = OH), reactions could lead to increased or decreased O3 loss.
a. Give an example of a reaction between X or XO with X’ or X’O (where X ≠ X’) that will decrease ozone loss. Explain how this reaction decreases ozone loss (compared to having just independent single catalyst cycles).
b. An example of a reaction between X/XO and X’/X’O (where X ≠ X’) that increases ozone loss over independent cycles is where X = Cl and X’ = Br in a Mechanism II reaction. Explain i) why one would see additional ozone loss over independent cycles? and ii) what species could possibly be measured to indicate if this reaction occurs to a significant extent?
2. Two key steps in ozone hole reactions are: 1) activation of Cl from reservoir species and 2) removal of compounds that are capable of inactivating Cl.
a) Give one reservoir species that will activate Cl in ozone hole chemistry and explain (words or reactions) how Cl is reactivated.
b) Give the species removed in ozone holes that could otherwise inactivate Cl.
3. Mechanism II is not very important in the upper tropical stratosphere despite there being sunlight for photolysis. Give one reason why mechanism II is not important under those conditions.