Ozone

Question 1

What is the molecular formula for ozone?

Answer 1

O₃

Question 2

What is the ozone layer?

Answer 2

A layer of O₃ surrounding the planet that absorbs very HIGH energy UV radiation (that’s harmful)

Question 3

What does CFCs stand for?

Answer 3

Chlorofluorocarbons

Question 4

Explain what CFCs are responsible for and are used for?

Answer 4

Chlorofluorocarbons in the atmosphere DEPLETE the ozone layer

They are man-made chemicals

USES:
> solvents
> coolants

Question 5

How is ozone made? What reactions are involved?

Answer 5

Ozone is made naturally when O₂ absorbs UV radiation in the following reactions…

1) Initiation
UV
O₂ ――> 2O*

2)
UV
O₂ + O* ――> O₃

Question 6

How do CFCs deplete the ozone layer? What are the reactions involved?

Answer 6

1) CFCs break up in the atmosphere to form chlorine radicals.
CF₂Cl₂ ――> CF₂Cl* + Cl*

2) Chlorine radicals react with ozone
O₃ + Cl* ――> O₂ + ClO*

3) Chlorine radicals are regenerated
ClO * + O₃ ――> 2O₂ + Cl*

Overall Reaction:
2O₃ ――> 3O₂

Question 7

When a CFC such as CF₂Cl₂ breaks up, why are fluorine radicals not formed? [2 marks]

Answer 7

Because the C-F bond had a higher bond enthalpy so is too strong to be broken - requires more energy.

C-Cl bond is broken because it is weaker than the C-F bond AND C-H bonds.

Question 8

(a) Identify the condition that causes a bond in CCl₄ to break in the upper atmosphere.

(b) Deduce an equation for the formation of the reactive species [2 marks]

(c) One of the reactive species formed from CCl₄ acts as a catalyst in the decomposition of ozone.

Write 2 equations to show how this species acts as a catalyst [2 marks]

Answer 8

(a) High energy UV radiation

(b) CCl₄ ――> CCl₃ * + Cl*

(c)
O₃ + Cl* ――> ClO* + O₂
O₃ + ClO* ――> Cl* + 2O₂