Alkanes

Question 1

What are Alkanes?

Answer 1

Alkanes are saturated hydrocarbons with the general formula CnH2n+2

Question 2

Describe the process of of the Fractional Distillation of Crude Oil

Answer 2

Crude oil, a mixture of different length hydrocarbons, is vaporised using a furnace to about 350°C.
The vaporised oil enters the temperature gradient column and rises through the trays.
As the vapour rises parts of the mixture condense at different levels.

Question 3

Why do the fractions condense at different levels in Fractional Distillation?

Answer 3

Fractions condense at different levels in fractional distillation because the hydrocarbons in crude oil are of different lengths so they will have different boiling points.

Question 4

Name two fractions of fractional distillation and their uses

Answer 4

Two from:
Gas - stove gas
Kerosene - jet fuel
Petrol - cars
Bitumen - tarmac
Diesel oil - diesel fuel
Fuel oil - power stations

Question 5

What is cracking?

Answer 5

Cracking is the breaking of long chain hydrocarbons into highly demanded shorter hydrocarbons

Question 6

What conditions are required for Thermal Cracking?

Answer 6

High temperature (1000°C) and high pressure (70atm)

Question 7

What are the main products of Thermal Cracking?

Answer 7

Alkanes used to make polymers (ex, plastics)

Question 8

What conditions are required for Catalytic Cracking?

Answer 8

High temperature (450°C) and slight pressure

Question 9

What catalyst is used in Catalytic Cracking and why?

Answer 9

A zeolite catalyst is used to lower the temperature needed for catalytic cracking, hence costs are lowered and the process speeds up.

Question 10

What are the main products of Catalytic Cracking?

Answer 10

Aromatic hydrocarbons useful in fuels for vehicles

Question 11

Describe the complete combustion of alkanes

Answer 11

Alkanes burn in oxygen completely to form carbon dioxide and water.
A large amount of energy is produced which is used to power vehicles and generate electricity.

Question 12

Describe the incomplete combustion of alkanes

Answer 12

When alkanes burn with a limited oxygen supply carbon monoxide and carbon (soot) are produced.
Carbon monoxide is poisonous as it bond to the haemoglobin on red blood cells and prevents oxygen bonding.
Soot causes breathing problems and clogs up engines.

Question 13

What is the name given to the gases that are given off when burning fossil fuels?

Answer 13

Greenhouse gasses

Question 14

What is the Greenhouse Effect?

Answer 14

Carbon dioxide absorbs infra red radiation from the Sun but simultaneously emits some of it back into the Earth.

Question 15

What is the name given to the increasing global temperatures caused by an increasing amount of carbon dioxide in the atnosphere?

Answer 15

Global warming

Question 16

How is Photochemical Smog produced?

Answer 16

Ozone occurs in the lowest level of the atmosphere, and is produced by the mixing of sunlight, hydrocarbons and nitrogen dioxide.
Mixing solid carbon particulates and ozone creates photochemical smog.

Question 17

What are the damaging capabilities of Photochemical Smog and Ozone?

Answer 17

Photochemical smog harms the respiratory system in animals and can cause damage to plants.
Ozone is toxic to humans.

Question 18

How are nitrogen oxides produced?

Answer 18

Car engines provide high pressure and temperature for nitrogen and oxygen found in the air to combine under producing nitrogen oxides.

Question 19

What do catalytic convertors do?

Answer 19

Catalytic convertors help to reduce the amount of unburnt hydrocarbons and nitrogen oxides going into the atmosphere

Question 20

How is acid rain formed?

Answer 20

Fossil fuels, containing sulfur based impurities, when burned react with oxygen to produce sulfur dioxide, an acidic gas.
Sulfur dioxide reacts with water in the atmosphere to form sulfuric acid which falls as acid rain.

Question 21

Name three negative consequences of acid rain

Answer 21

Damages plants
Kills fish
Erodes buildings

Question 22

What is wet scrubbing?

Answer 22

An alkali is used to neutralise sulfur dioxide in flue gasses. This involves dissolving calcium carbonate/oxide in water and spraying it on acidic sulfur dioxide gas.

Question 23

What is the Initiation stage of Free Radical Chain Reactions?

Answer 23

Radicals are produced normally using visible light or ultra violet light. This is a photochemical reaction. The bond breaks producing 2 radicals.

Question 24

What is the Propagation stage of Free Radical Chain Reactions?

Answer 24

When a radical reacts with a non-radical molecule new radicals are created which then go on to react with other non-radicals, hence why this is a chain reaction.

Question 25

What is the Termination stage of Free Radical Chain Reactions?

Answer 25

When 2 radicals react the from a non-radical molecule. Tis ends the chain reaction.