organohalogen compounds in the environment

what are the most common organohalogens?

chloroflurocarbons (CFCs)

what were three commercial uses of CFCs and why?

refrigerants, propellants for aerosols, solvents for dry cleaning
CFCs are chemically inert as they are non-flammable and non-toxic

what is the behaviour of ozone in the stratosphere?

ozone is continually being formed and broken down by UV radiation, where oxygen molecules are broken into oxygen radicals - O2 -> 2O
oxygen and oxygen radicals forms ozone which then breaks down
O2 + O ⇌ O3

how do CFCs deplete the ozone layer?

CFCs break down to form chlorine radicals that catalyse the break down of ozone

what are the two steps for the breakdown of ozone by CFCs?

initiation and propagation

what is the process of initiation for the breakdown of ozone by CFCs?

sunlight breaks the C-Cl bond in a CFC molecules and produces 2 radicals
CF2CL2 → CFCL2• + Cl•

what is the process of propagation for the breakdown of ozone by CFCs?

step 1: the Cl• reacts with O3 to form the ClO• intermediate and O2
Cl• + O3 → ClO• + O2
step 2: the ClO• reacts with more O3 to make O2 and Cl•
ClO• + O → Cl• + O2

what is the overall equation for the breakdown of ozone by CFCs?

O3 + O → 2O2

what other radical can also catalyse the breakdown of ozone?

nitrogen oxide radicals formed during lightning strikes and aircraft travel

what are the two propagation equations for the breakdown of ozone by nitrogen oxide radicals?

NO• + O3 → NO2• + O2
NO2• + O → NO• + O2

what is the overall equation for the breakdown of ozone by nitrogen oxide radicals?

O3 + O → 2O2

why is ozone harmful to humans?

ozone absorbs most harmful UV radiation that causes skin cancer

what alternative to CFCs is now used?

hydrofluorocarbons as they don’t contain chlorine atoms, so will not effect the ozone layer