Environmental Concerns from the use of Organohalogen Compounds

Question 1

what are the use of organohalogen compounds?

Answer 1

• pesticides
• general solvents
• refrigerators
• flame retardants
• aerosol propellants

Question 2

what are organohalogens?

Answer 2

molecules that contain at least on halogen joined to a carbon chain

Question 3

what is the role of the ozone layer?

Answer 3

absorbs most of the UV radiation(UV-B)
- UV-B is linked to sunburn

Question 4

what does the complete depletion of the ozone mean?

Answer 4

allows more UV-B radiation to reach the Earth’s surface
- which can lead to an increase in genetic damage and greater risk of skin cancer in humans

Question 5

where is ozone formed?

Answer 5

• in the stratosphere(above the troposphere) the ozone is being formed and broken down by action of UV radiation

Question 6

what happens when there is high energy of UV?

Answer 6

• UV breaks down oxygen molecules to oxygen radicals
• O2 –> 2O(radical)

Question 7

what happens at a steady state? and what happens to equilibrium when humans produce and use CFC’s?

Answer 7

• rate of formation of ozone is the same rate as when oxygen radicals are broken
• O2 + O(radical) <–> O3, this equilibrium changes when we use or produce CFC’s

Question 8

what are chlorofluorocarbons (CFC’s)?

Answer 8

• they are very stable due to the strength of carbon-halogen bonds

Question 9

how long are CFC’s stable for?

Answer 9

• they are only stable until they reach the stratosphere
• at the stratosphere the CFC’s break down and chlorine radicals are formed

Question 10

what are the uses of chlorine radicals?

Answer 10

• catalyse the breakdown of the ozone layer

Question 11

what happens to CFC’s at the stratosphere?

Answer 11

• UV radiation provides sufficient energy to break carbon-halogen bond in CFC’s by homolytic fission to form radicals

Question 12

what is the photodissociation of CF2CL2?

Answer 12

CF2Cl2 –> CF2Cl* + Cl*

Question 13

what is the intermediate in the photodissociation of CFC’s?

Answer 13

Cl*
- this reacts with ozone molecule, breaking the ozone into oxygen
- *ClO + O3 –> *ClO + O2

Question 14

what are the propagation steps for the breakdown of the ozone? and what is the overall equation?

Answer 14

Cl* + O3 –> ClO* + O2
ClO* + O –> Cl* + O2
- regenerates a chlorine radical which can react with an ozone
OVERALL: O3 –> 2O2

Question 15

what are the molecules that can cause the breakdown of ozone?

Answer 15

• chlroine radicals
• nitrogen oxide radicals

Question 16

what are nitrogen oxide radicals?

Answer 16

• naturally occurring during lightning strikes

Question 17

what are the propagation steps for the nitrogen oxide radicals? and what is the overall equation?

Answer 17

NO* + O3 –> NO2* + O2
NO2* + O –> NO* + O2

OVERALL: O3 + O –> O2
- radical acts as a catalyst (the overall equation is the same in both)