Haloalkanes (synthesis of chloroalkanes)

Question 1

What are the causes of the depletion of our ozone layer?

Answer 1

The release of free radicals, the use of CFC’s, the excessive burning of fossil fuels

Question 2

What are the three stages of the reaction mechanism?

Answer 2

Initiation, Propagation and Termination

Question 3

Define photodissociation

Answer 3

The sunlight energy which provides energy to break the Cl-Cl bond

Question 4

What is the chemical reaction that displays how ozone is created?

Answer 4

UV + O2 –> 2O + heat / O2 + O –> O3 / O3 + O –> 2O2

Question 5

Which reactions demonstrate the destruction of the ozone layer?

Answer 5

Cl2 2Cl•
Cl• + O3 –> ClO• + O2
ClO• + O3 –> 2O2 + Cl•

Question 6

How do CFC’s destroy the ozone layer?

Answer 6

The atomic chlorine freed from CFC reacts in a catalytic manner with ozone and atomic oxygen to make more oxygen molecules

Question 7

Chlorofluorocarbons (CFCs) and chloroalkanes can be used as what?

Answer 7

Solvents- they both used to be used in dry cleaning and degreasing.

Question 8

Give the end products of the following reactions.
Cl.+CH3. —–>
CH3.+CH3. —–>

Answer 8

Cl.+CH3. —–> CH3Cl

CH3.+CH3. —–>C2H6

Question 9

What factor is responsible for breaking up stable molecules?

Answer 9

Ultraviolet rays from the sun

Question 10

Ultraviolet rays can cause what kinds of medical problems?

Answer 10

Sunburn, skin cancer, eye cataracts, premature ageing

Question 11

Explain what is meant by the term substitution

Answer 11

Replacement of one atom or group of atoms by another

Question 12

What is a photochemical reaction?

Answer 12

Halogens reacting with alkanes in the presence of UV light.

Question 13

The first part of the propagation step is outlined below. What is the second part?
Cl.+CH4 —–> CH3.+HCl

Answer 13

CH3.+Cl2 —–> CH3Cl+Cl.

Question 14

What will be produced if methane is in excess?

Answer 14

Mostly chloromethane

Question 15

What will be produced if chlorine is in excess?

Answer 15

Dichloromethane CH2Cl2, trichloromethane CHCl3 and tetrachloromethane CCl4. This is because the Cl. free radicals attack the chloromethane molecules.

Question 16

Chlorofluorocarbons (CFCs) and chloroalkanes can be used as what?

Answer 16

Solvents- they both used to be used in dry cleaning and degreasing.

Question 17

Give the end products of the following reactions.
Cl.+CH3. —–>
CH3.+CH3. —–>

Answer 17

Cl.+CH3. —–> CH3Cl

CH3.+CH3. —–>C2H6

Question 18

What are the properties of CFCs?

Answer 18

Un reactive, non flammable and non toxic

Question 19

Why is the ozone layer important?

Answer 19

The ozone, formed naturally in the upper atmosphere, absorbs ultraviolet radiation, preventing most of it from reaching the ground. (Protects us from skin cancer)

Question 20

What is a CFC?

Answer 20

A haloalkane molecule that has H atoms replaced by Cl or F atoms.

Question 21

What are CFCs used for?

Answer 21

Used as solvents and in aerosols

Question 22

Explain what is meant by the term homolytic

Answer 22

Breaking a covalent bond evenly so that one electron goes to each atom

Question 23

Explain what is meant by the term free radical

Answer 23

A species with an unpaired electron

Question 24

Explain what is meant by the term substitution

Answer 24

Replacement of one atom or group of atoms by another

Question 25

How do CFCs cause ozone depletion?

Answer 25

The Cl• free radicals react with the ozone in the upper atmosphere and remove it, causing the so-called hole in the ozone layer.
The chlorine free radical is effectively behaving as a catalyst in that it is regenerated at the end of the reaction. This allows one chlorine free radical to cause the breakdown of hundreds of ozone molecules, before finally meeting another free radical (termination).

Question 26

What are the alternatives to CFCs?

Answer 26

Hydrochlorofluorocarbons (HCFCs) and Hydrofluorocarbons (HFCs)