Depletion of the ozone layer

Question 1

CFC symbol

Answer 1

CF₂Cl₂

Question 2

Where is the ozone layer?

Answer 2

The ozone layer is in the stratosphere. There are only tiny amounts of ozone in this layer, but it still absorbs most of the ultraviolet (UV) radiation from the Sun.

Question 3

What happens as the ozone layer gets depleted?

Answer 3

The more depleted the layer of ozone gets, the more UV light can get through to the Earth’s surface.

Question 4

How have the opinions of chlorofluorocarbons changed?

Answer 4

• When chlorofluorocarbons (CFCs) were first discovered, they were thought to be totally safe.
• Scientists now know that CFC molecules slowly move upwards, into the stratosphere where they attack the ozone layer.
• Society agreed with the scientists’ views that it is CFCs that deplete the ozone layer. This is why the use of CFCs has been banned in the UK but is a global problem.

Question 5

What can replace CFCs?

Answer 5

CFCs can be replaced with alkanes or hydrofluorocarbons (HFCs) which will not damage the ozone layer.

Question 6

How does ozone work?

Answer 6

• UV radiation is part of the electromagnetic spectrum. Visible light can pass through the ozone layer easily, but UV radiation is absorbed by it.
• The UV part of the electromagnetic spectrum has exactly the right frequency to make ozone molecules vibrate.
• The energy of the UV radiation is converted into movement energy inside each molecule.
• The thicker the ozone layer, the more radiation is absorbed.

Question 7

History of CFCs

Answer 7

• When CFCs were discovered in the 1930s, scientists were excited because these substances were inert.
• In the 1970s scientist began to link the depletion of the ozone layer with the CFCs.

Question 8

What happens to the stratosphere to CFCs?

Answer 8

• In the stratosphere, the UV radiation from the sun breaks down the CFC molecules to give highly reactive chlorine atoms. A single chlorine atom is called a chlorine radical.
• These chlorine atoms react with ozone molecules, turning the ozone back into oxygen gas and depleting the ozone layer.
• Chlorine atoms are regenerated so they can react with more ozone molecules.
• UV light breaks down CFCs very slowly, so they last for a long time.
• CF₂Cl₂ ⇒UV ⇒ CF₂Cl + Cl•

Question 9

The main choices are for alternatives to CFCs are

Answer 9

Alkanes and HFCs. HCFs do not contain chlorine, so they cannot make chlorine radicals which is safer.

Question 10

When a covalent bond breaks

Answer 10

It can split into equal halves to make radicals.

Question 11

What does UV cause?

Answer 11

UV radiation causes radicals. Each radical sets of a chain reaction. One chlorine radical causes the breakdown of more than 100,000 ozone molecules

Question 12

The chain reaction has three stages:

Answer 12

1. UV light breaks a bond in CFC molecules to form chlorine radicals.
2. Chlorine radicals react with ozone molecules, creating more chlorine Radicals.

Cl• + O₃ ⇒ OCl• + O₂

OCl• + O₃ ⇒ Cl• + 2O₂

Combining these two equations gives: 2O₃ ⇒ 3O₂

3.One possible termination reaction is: Cl• + Cl• ⇒ Cl₂

Question 13

How long do CFCs last?

Answer 13

It is common for CFCs to last 20 to 50 years before they are broken down by UV radiation. CFCs will continue to deplete ozones long after they have been banned.