3 - Ozone depletion

Question 1

Where is the ozone layer found?

Answer 1

In the upper atmosphere

Question 2

Why is the ozone layer beneficial?

Answer 2

It acts as a protective barrier by absorbing UV radiation, preventing harm to life on earth

Question 3

What are chlorofluorocarbons (CFC’s)?

Answer 3

A type of halogenoalkane that contains only carbon, fluorine and chlorine

Question 4

What were CFC’s used for before they were banned?

Answer 4

• Refridgerants
• Propellants
• Solvents

Question 5

What 4 properties of CFC’s made them useful?

Answer 5

• High stability due to C-X bond
• Low toxicity
• Non-flammable
• Volatile so easily vapourised

Question 6

Why was the use of CFC’s banned?

Answer 6

When CFC’s reach the upper atmosphere ozone layer they break down and form radicals
These radicals destroy the ozone layer

Question 7

How do CFC’s destroy the ozone layer?

Answer 7

Energy from UV radiation causes the C-Cl bonds in CFC’s to break forming a chlorine free radical

Question 8

Write the 2 equations and the overall equation of the process of chlorine free radicals catalysing the decomposition of ozone

Answer 8

Cl radicals will react with ozone:
Cl^. + O₃ → ClO^. + O₂

The Cl radical is regenerated:
ClO^. + O₃ → 2O₂ + Cl^.

Overall: 2O₃ → 3O₂

Question 9

How do chlorine radicals act as a catalyst in the decomposition of ozone?

Answer 9

They provide an alternative route with a lower activation energy