Chapter 15

Question 1

What is an organohalogen compound ?

Answer 1

• organohalogen compounds are compounds that contain at least one halogen atom joined to carbon chain

Question 2

What happens in the stratosphere ?

Answer 2

• Oxone is continuously being made and broken by UV
• very high energy UV breaks O2 to form oxygen radicals
• A steady state forms rate of formation of ozone = rate at the breaking down for ozone
• O₂ + O -> O₃

Question 3

What happens with CFCs and the Ozone?

Answer 3

• CFC’s - Chlorofluorocarbons
• CFC’s remain stable until the stratosphere where they break down, forming Chlorine radicals
• these catalyse the breakdown of the ozone layer

Question 4

What is the reactions that happen in the ozone with CFC’s ?

Answer 4

• due to the stability of CFC’s, they can spend a long time in the troposphere
• once they reach the stratosphere, once here the UV gives the necessary energy to break C-halogen -> homolytic fission
• C-Cl has lowest bond enthalpy so breaks first
• photodissociation radiation starts the breakdown

Question 5

What are the radical steps in the ozone ?

Answer 5

CF₂Cl₂ -> CF₂Cl (radical) + Cl (radical)
- chlorine radical is formed which is very reactive
- it will react with an ozone molecule:
1) Cl (radical) + O₃ -> ClO(radical) + O₂
2) ClO (radical) + O -> Cl (radical) + O₂
3) overall: O₃ + O -> 2O₂

Question 6

What are the other radicals that catalyse the breakdown of ozone ?

Answer 6

• Nitrogen dioxide radical are formed naturally during a lighting strike and aircraft in stratosphere
• NO radical causes breakdown of ozone
  1) NO(radical) + O₃ -> NO₂ (radical) + O₂
  2) NO₂(radical) + O -> NO(radical) + O₂
  3) overall: O₃ + O -> 2O₂