Freon

From Chempedia

Ozone Depletion from Freon

Nathan Davis
Chantha Tes

Freons, more commonly known as CFCs or chlorofluorocarbons, are Haloalkanes consisting of an alkane linked with one or more halogens[1]. Due to the generally inert nature of Freon, they are used as propellants and have served in many applications including fire extinguishers, aerosol accelerants and refrigerants. While production of aerosol sprays that use Freons has been banned in the United States, Freons are still commonly used in third world countries throughout the world[2]. Commonly used Freons include CFC-11, CFC-12, CFC-113, CFC-114, and CFC-115. The major concern over Freons is their impact on the ozone levels in the troposphere and stratosphere of Earth\’s atmosphere.

Image:freon_1.jpg

CFC11 and O3 Decomposition[3] CFC11, a common Freon decomposes in the troposphere of the Earth. This chemical reaction takes on this form:

CFCl3+ hν → CFCl2 + Cl

One molecule of CFC11 breaks down into CFC12 plus a highly reactive Cl free radical. This reaction only takes place in the troposphere where the light photons from the sun have enough energy to break apart the molecule.

After CFC11 is broken down, the Cl free radical interacts with O3 to produce ClO + O2:

Cl + O3 → ClO + O2

The resulting ClO molecule then further reacts with O3 in the following manner:

O3 + hν -> O + O2 ClO + O -> Cl + O2 O + O3 -> O2 + O2

Environmental Impacts of Ozone Depletion Ozone acts as a buffer between the sun’s energy and the Earth’s surface, blocking a significant amount of UV radiation from reaching the Earth’s surface. Uninhibited, this excessive UV radiation would have negative health effects. As a secondary effect, depletion of ozone can lead to global warming. When holes form in the ozone layer, UV radiation is able to pass through unimpeded. This radiation then stays trapped between the Earth’s surface and the ozone causing a net increase in heat[4].

Image:freon_2.gif

Ozone Regeneration and Decreasing O3 Depletion Contrary to popular belief, ozone will regenerate without the presence of other ozone molecules. Ozone is formed by the following process:

Image:freon_3.jpg

This process takes place at a very slow pace is comparison to the rapid rate that the catalyzed decomposition of ozone takes place at. This results in a net breakdown of ozone molecules.

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Footnotes

  1. ^ Haloalkanes-1, http://www.chem.ucalgary.ca/courses/351/Carey5th/nomenclature/halkanes/halkanes-1.html (accessed 9/26/05).
  2. ^ Energy and Global Warming, http://www.is.wayne.edu/drbowen/thw01/GlobalWarming.htm (accessed 9/26/05).
  3. ^ Ozone in the Atmosphere, http://www.science.uwaterloo.ca/~cchieh/cact/applychem/ozone.html (accessed 9/26/05).
  4. ^ Global waming, www.ecocentre.org.uk/images/ozone.gif (accessed on 9/26/05).
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