CFCs

Question 1

How do CFCs destroy ozone

Answer 1

CFCs break down to chlorine radicals to catalyse break down of ozone

Question 2

What is the initiation step in this reaction- How do Cl radicals form?

Answer 2

Sunlight (UV) breaks the C-Cl bond in CFC molecule and produces two radicals.

Question 3

Initiation Equation: CFC breakdown

Answer 3

CCl3F + UV –> ‘CCl2F + Cl’

Question 4

CFC + Ozone Propagation step 1

Answer 4

Cl’ + O3 –> O2 + ClO’

Question 5

CFC + Ozone propagation step 2

Answer 5

ClO’ + O –> O2 + Cl’

Question 6

Overall Equation for Cl’ + O3

Answer 6

O3 + O –> 2O2
Cl’ is a catalyst.

Question 7

What other radicals destroy ozone?

Answer 7

Nitrogen oxide radicals

Question 8

Equation for nitrogen oxide radical formation

Answer 8

NO2 + UV –> NO’ + O

Question 9

NO’ + O3 propagation step 1

Answer 9

NO’ + O3 –> O2 + NO2’

Question 10

Nitrogen Oxide Propagation step 2

Answer 10

NO2’ + O –> NO’ + O2

Question 11

NO overall equation

Answer 11

O3 + O –> 2O2

Question 12

Where does the O come from in the propagation steps?

Answer 12

O is formed when O2 in the atmosphere is broken down by UV.

Question 13

Original uses of CFCs

Answer 13

1. In fridges as refrigerants
2. As propellant in deodorant.

Question 14

What restricted use of CFCs?

Answer 14

Montreal treaty signed 1987 and came in 1989-introduced steps for complete removal of CFCs.

Question 15

Alternatives to CFCs (with their own issues)

Answer 15

1. HFCs (hydrofluorocarbons)- don’t have chlorine. However, are potent greenhouse gases.
2. Hydrocarbons - However greenhouse gases.

Question 16

What we use instead nowadays

Answer 16

1. Pump sprays and inert gases e.g. N2 as propellants
2. Ammonia used as refrigerant.