3.3.2. Alkanes

Question 1

What is a saturated hydrocarbon?

Answer 1

A hydrocarbon with only single bonds

Question 2

What is crude oil?

Answer 2

A mixture of mainly alkanes that can be separated by fractional distillation

Question 3

What is fractional distillation?

Answer 3

The process of separating the alkanes in crude oil by use of their different melting points

Question 4

What is cracking?

Answer 4

The process of breaking C-C bonds in alkanes to make shorter molecules

Question 5

What are the two types of cracking?

Answer 5

Thermal cracking and catalytic cracking

Question 6

How is thermal cracking carried out?

Answer 6

At high pressure and temperature

Question 7

What is thermal cracking used for?

Answer 7

Producing a high percentage of alkenes

Question 8

How is catalytic cracking carried out?

Answer 8

Slight pressure, high temperature, zeolite catalyst

Question 9

What is catalytic cracking used for?

Answer 9

Production of motor fuels and aromatic hydrocarbons

Question 10

Why is cracking carried out?

Answer 10

The products of cracking are in greater demand than the long chain alkanes

Question 11

What is combustion?

Answer 11

The exothermic reaction of a fuel with oxygen

Question 12

What is complete combustion?

Answer 12

A combustion reaction where there is enough oxygen to ensure products are purely carbon dioxide and water

Question 13

What is incomplete combustion?

Answer 13

A combustion reaction where the lack of oxygen results in products other than carbon dioxide and water

Question 14

What can the products of incomplete combustion be?

Answer 14

Carbon monoxide, carbon

Question 15

Which pollutants are produced by the internal combustion engine?

Answer 15

Nitrogen oxides, carbon monoxide, carbon, unburned hydrocarbons

Question 16

What is the purpose of a catalytic convertor?

Answer 16

To remove gaseous pollutants produced by internal combustion engines

Question 17

How is sulphur dioxide released from combustion engines?

Answer 17

Through the combustion of hydrocarbons containing sulphur impurities

Question 18

What is a flue gas?

Answer 18

The gas released from large industrial plants and power plants

Question 19

How can sulphur dioxide be removed from flue gases?

Answer 19

By using calcium oxide or calcium carbonate to neutralise it

Question 20

What is a free radical?

Answer 20

A reactive species containing an unpaired electron

Question 21

How are chlorine free radicals produced?

Answer 21

Exposure to UV light

Question 22

What is free radical substitution?

Answer 22

Where an atom bonded to a carbon is substituted for a free radical atom

Question 23

Which steps are involved in a free radical substitution?

Answer 23

Initiation, propagation, termination

Question 24

What is an initiation step?

Answer 24

The generation of a free radical

Question 25

Give an example of an initiation step

Answer 25

Cl? ? 2Cl?

Question 26

What is a propagation?

Answer 26

Intermediate steps in a free radical reaction which cause the regeneration of the original free radical

Question 27

Give an example of a propagation step

Answer 27

CH? + Cl? ? CH?? + HCl, CH?? + Cl? ? CH?Cl + Cl?

Question 28

What is a termination?

Answer 28

A reaction involving two free radicals and resulting in no free radicals

Question 29

Give an example of a termination step

Answer 29

CH?? + Cl? ? CH?Cl

Question 30

Why do free radical substitutions result in impure products?

Answer 30

Because there are many possible side reactions e.g. further substitution with chlorine or alkyl radical-radical reactions