Chem and the Environment supp

Chem and the Environment supp - Chemistry and the...

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Chemistry and the Environment (Supplement) Spring 2084 1. Background. a) Although there are many natural chemical cycles (N, C) and naturally generated pollutants (SO 2 , H 2 S from volcanoes; CO 2 from forest fires; NO and NO 2 and O 3 from lightning) humankind has succeeded in creating massive environmental problems of many kinds over the past two centuries. 2. Atmospheric Composition. a) At sea level, dry air consists of the following percentages by volume: N 2 78.03 O 2 20.99 Ar 0.94 CO 2 0.033 Ne, He, Kr, Xe ~0.002 b) The different regions of the atmosphere are hosts to different kinds of chemical processes. i) 0 to 10 km: Troposhpere: contains 80 % of total mass and almost all of the water vapor. Temperature decreases almost linearly from 0 to 10 km above earth’s surface. ii) 10 to 50 km: Stratosphere: consists of nitrogen, oxygen, and ozone. Temperature increases with altitude due to exothermic chemical reactions. iii) 50 to 200 km: Mesophere: low concentration of gases; temperature decreases with altitude. iv) above 200 km: Thermosphere: temperature again increases due to bombardment of N 2 , N, O 2 by electrons, protons from sun; Recombinations such as those below are exothermic: 2 N N 2 N + + e N + 2 O + e O 2 c) Note: Above 90 km, a series of photoionizations and photodissociations absorb dangerous photons. λ < 242 nm O 2(g) 2 O (g) photo dissociation λ max = 134.5 nm NO(g) + + ) g ( NO + photoionization N 2 + + 2 N + λ max = 80.1 nm
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Chemistry and the Environment (Supplement) Spring 2084 d) Example Calculation: The bond dissociation energy of O 2(g) is 498.7 kJ/mol. What is the maximum λ needed for a photon to dissociate an O
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This note was uploaded on 04/07/2008 for the course CHEM 0970 taught by Professor Kogut during the Spring '08 term at Pittsburgh.

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Chem and the Environment supp - Chemistry and the...

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