Ozone

Question 1

Why is the ozone upper layer important

Answer 1

Filters out harmful UV radiation from the sun

Question 2

Why is the ozone bottom layer harmful

Answer 2

Pollutant and contributes to smog formation

Question 3

Why are man made CFCs harmful?

Answer 3

They contribute to forming a hole in the ozone layer
This is because it causes chlorine free radicals to form in the upper atmosphere when UV light causes the C-CL bond to break in CFCs
Chlorine free radicals catalyse the decomposition of ozone
CF2CL2 = CF2Cl :+ Cl:

Question 4

How do chlorine free radicals contribute to the decomposition of ozone in the upper layer

Answer 4

The chlorine free radicals catalyse the decomposition of ozone as they are regenerated
They provide an alternative route with a lower activation energy

Question 5

Give equations of chlorine free radicals reacting with ozone and the overall equation

Answer 5

Cl: + O3 = ClO:+ O2
ClO:+ O3= 2O2+ Cl:
Overall equation= 2O3 = 3O2
The regenerated chlorine free radical means one Cl radical can destroy thousands of ozone molecule

Question 6

What is used now as a replacement for CFCs?

Answer 6

HFCs hydrogen flouro carbons
Used for refridgerators as they dont contain the C-Cl bond which could be broken easily due to UV light to produce chlorine free radicals
The C-F bond is stronger and is not affacted byb UV light
This means ozone depletion if now minimised and global warming is prevented

Question 7

Give initiation equation for cfcs free rad

Answer 7

CF2Cl2= CF2Cl+ :Cl
Homolytic fission
Under UV light

Question 8

Give propagation equation for cfcs free rad

Answer 8

;Cl+ O3= O2+ ClO:
ClO:+ O3= 2O2+Cl:
Catalyst for chain reaction

Question 9

Give termination equation for cfcs free rad

Answer 9

;Cl+:Cl= Cl2

Question 10

Overall eq depletion

Answer 10

2O3= 3O2