4. haloalkanes and the environment Flashcards
what are CFCs
haloalkane
Chlorofluorocarbons
contain only chlorine fluorine and carbon
why did we stop using CFCs
destroy ozone layer
ozone O3 purpose
chemical sunscreen
absorbs UV which causes sunburn/skincancer
how is ozone formed
naturally when a O2 molecule is broken down into 2 free radicals by UV radiation.
free radicals attack O2 molecules forming ozone
O2->O+O
O2+O->O3
how were CFCs causing destruction of ozone
- CFCs absorb UV radiation and split to form chlorine free radicals
- chlorine free radicals catalyse destruction of ozone- destroy ozone and are regenerated to destroy more ozone
mecanism for CFC’s destroying ozone
- chlorine free radicals *Cl formed when C-Cl bonds in CFCs broken by UV radiation
CF2Cl2(g) -> *CF2Cl(g) + *Cl(g) - free radicals are catalysts. react with ozone to form intermediate *ClO & an Oxygen molecule
*Cl(g) + O3(g) -> O2(g) + *ClO(g)
*ClO(g) + O(g) -> O2(g) + *Cl(g)
(O comes from break down of O2 by UV. *Cl(g) regenerated can attack more O3)
overall reaction of the breakdown of ozone by CFCs / or nitrogen oxide
O3(g) + O(g) -> 2O2(g)
other than CFCs what else can break ozone down
*NO free radicals from Nitrogen oxides
Nitrogen oxides are produced by
car and aircraft engines.
thunderstorms.
general equations for break down of Ozone by CFCS of Nitrogen oxides
R + O3 -> RO + O2
RO + O -> R + O2
(O formed when UV breaks down O2)
alternatives to CFCS
HCFCs (hydrochlorofluorocarbons)
HFcs (hydroflourocarbons)
Hydrocarbonds
+ves and -ves to HCFCs
- still damage ozone (although less affect that CFCS)
greenhouse gas
+ves and -ves to HFCs
+ dont contain chlorine = dont affect ozone layer
- green house gas
-ves to hydrocarbons
greenhouse gases
aerosols replaced by
pump spray systems OR use nitrogen as propellant
