15.2 Organohalogen compounds in the environment Flashcards
(27 cards)
What are the properties of CFC’s that make it suitable for use as an aerosol?
-low reactivity, non flammable
-volatile
-non-toxic
-very stable
What are the two sources of nitrogen oxides in the stratosphere?
aircraft
lightening
What are the two sources of nitrogen oxides in the stratosphere?
aircraft
lightening
What are organohalogen compounds?
Molecules that contain at least one halogen atom joined to a carbon chain
What are the uses of organohalogen compounds?
-pesticides
Where is the ozone layer found?
Outer edge of the stratosphere
What is the formula of ozone?
O3
What does the ozone layer do?
Absorbs most of the biologically damaging UV-B radiation allowing only a small amount to reach the Earths surface
What will happen is there is continued depletion of the ozone layer?
More UV-B rates will reach Earths surface, causing sunburn, genetic damage and skin cancer is humans
How is ozone broken down?
By ultraviolet (UV) radiation
What are the equations showing the equilibrium of ozone formation and breakdown
O2 + O ⇌ O3
How is the ozone equilibrium beign upset?
Human activity, rate of ozone breakdown (O2 → 2O radicals) if more than ozone formation (O2 + O ⇌ O3)
How do CFC’s affect the ozone layer?
They remain stable until they reach the stratosphere where they begin to break down due to UV light, which provides energy to brea the C-X bond by homolytic fission and form chlorine radicals which catalyse the breakdown of the ozone layer
What are CFCs?
Chlorofluorocarbons, contain chlorine, fluorine and carbon
What are the uses of CFCs?
Coolants in fridges, propellants in aerosols, dry cleaning solvents, degreasing circuit boards
Why are CFCs so stable?
Due to the strength of the carbon-halogen bonds
How many ozone molecules are broken down by 1 CFC?
1 CFC can break down 100 000 ozone molecules (estimate)
What is the initiation reaction for breakdown of ozone?
-radiation initiates the breakdown of CFCs by photodissociation
What are the propagation steps for the breakdown of ozone by CFCS
Why is the C-Cl bond broken down first in the breakdown of CFCs to catalyse the breakdown of ozone?
It has the lowest bond enthalphy
What is the overall equation for the breakdown of ozone by CFCs?
Are CFCs the only one responsive for the breakdown of ozone?
No, other radicals catalyse the breakdown of ozone like nitrogen oxide radicals
How are nitrogen oxide radicals formed?
During lightning strokes, as a result of aircraft travel is the stratosphere
