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Unformatted text preview: ce toxic and corrosive ammonia and sulfur dioxide then in commercial use as
refrigerants. Fluorocarbon-12 (CF2 Cl 2 ) was their answer, and it quickly found application in refrigerators,
freezers, and air conditioners. In the 1950s, fluorocarbon-11 (CFCl3 ) became a basic propellant for the new
aerosol can industry, fostering the development of the spray can. Soon, it was also developed as a blowing agent
for Styrofoam in insulation, cushions, plastic furniture, and sealants. While there are many fluorocarbon
compounds, fluorocarbon-11 and fluorocarbon-12 find the widest applications. The advantage of CFCs was that
they were nontoxic, noncorrosive, and nonreactive.
There are no known chemical reactions in the troposphere that destroy CFCs. Because of their inertness,
CFCs accumulate in the troposphere and gradually diffuse up to the stratosphere. Since ozone filters out UV
light, there is more UV light in the ozone layer than below it. In the ozone layer CFCs are bombarded by highenergy UV radiation and break apart. This photodissociation of fluorocarbon molecules breaks a C—Cl bond,
and releases a chlorine atom. In the case of chlorofluorocarbon-12 the reaction is:
CCl 2 F 2 + h ν → C ClF 2 + C l Back Forward Main Menu TOC Study Guide TOC Textbook Website MHHE Website Chemistry in the Atmosphere 3 59
The Cl atom attacks an ozone molecule, converting it to the more stable oxygen molecule, and forming an
intermediate molecule, chlorine monoxide ClO. Compounding the problem is that once a chlorine atom has
destroyed an ozone molecule, then it is regenerated when the intermediate ClO reacts with an O atom. Recall
that O atoms are prevalent in the stratosphere.
Cl(g) + O3 (g) → ClO(g) + O2 (g)
ClO(g) + O(g) → O 2 (g) + Cl(g)
O(g) + O3 (g) → 2O 2 (g) net Since Cl atoms accelerate the destruction of ozone and are regenerated, they are true catalysts. An increased rate
of destruction of ozone has the expected effect of lowering the atmospheric ozone concentration.
The net result of ozone depletion is that...
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This note was uploaded on 09/15/2009 for the course CHEM 102 taught by Professor Bastos during the Spring '08 term at Adelphi.
- Spring '08