Chapter 15.2 - Ozone and organohalogen compounds

Question 1

Show how ozone is formed and broken by the action of UV radiation

Answer 1

1. O₂ -> 2O (radicals)
2. O₂ + O ⇌ O₃

Question 2

What are chlorofluorocarbons?

Answer 2

Compounds that contain carbon atoms with chlorine and fluorine atoms attached to them
E.g CCl₃F

Question 3

What are three uses of CFC?

Answer 3

1. Refrigerators
2. Propellants for aerosols
3. As solvents for dry cleaning

Question 4

Why do CFCs have many uses?

Answer 4

They are chemically inert as they are non-flammable and non-toxic

Question 5

Why do CFCs have devastating effects on the ozone layer?

Answer 5

1. They absorb a lot of UV radiation in the upper atmosphere
2. They are broken down by the UV light and form chlorine radicals (cl-cl has the lowest bond enthalpy and breaks)
3. Chlorine radicals react with ozone and break down the layer
   more uv radiation = increased genetic damage and risk of skin cancer in humans

Question 6

Write the equation that shows the break down of the ozone layer (Cl)

Answer 6

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

Question 7

Are CFCs responsible for all oxygen depleting reactions?

Answer 7

No as other radicals also catalyse the breakdown of ozone. For example nitrogen oxide radicals are formed naturally during lightning strikes

Question 8

Write the equation that shows the break down of the ozone layer (NO)

Answer 8

NO. + O₃ -> NO₂ + O₂
NO₂. + O -> NO. + O₂

Question 9

Write the overall equation that shows the break down of the ozone layer

Answer 9

O₃ + O -> 2O₂