SC20 Fuels

Question 1

Define hydrocarbon

Answer 1

A compound that contains hydrogen and carbon only

Question 2

What is crude oil?

Answer 2

• complex mixture of hydrocarbons of different sizes
• thick, sticky black liquid that is found in porous rock

Question 3

What is crude oil used for?

Answer 3

• fuel for vehicles such as aircraft, ship, heating and power stations
• feedstock or raw materials for the petrochemical industry

Question 4

Define petrochemicals

Answer 4

Substances made from crude oil, such as poly(ethene) and other polymers

Question 5

Define finite resource

Answer 5

Resources that are not made anymore (or are being made extremely slowly) which limits the amount available to us

Question 6

Why is crude oil a finite resource?

Answer 6

It is being used up faster than it is being produced

Question 7

Why is crude oil important fror the petrochemical industry?

Answer 7

• The fuels that are used in most modern methods of transport are all based on oil products
• these are all product obtained from crude oil

Question 8

Define non renewable

Answer 8

Fuels that are being used up faster than they can be formed

Question 9

How is crude oil formed?

Answer 9

• ancient remains of microscopic animals and plants that once lived in the sea
• became covered in layers of sediments
• the high temperatures and pressure caused the sediments to turn into rocks, therefore trapping the gas and the oil

Question 10

How do we separate crude oil into different hydrocarbon?

Answer 10

Using fractional distillation

Question 11

Describe how crude oil is separated by fractional distillation

Answer 11

• crude oil enters fractionating column, so vapours rise
• vapours with very high boiling points will immediately condense, into liquids lower down and are tapped off
• vapours of hydrocarbons with low boiling points will rise up and condense at the top of the column

Question 12

What are the different compounds obtained from crude oil?

Answer 12

• natural gas
• petrol
• kerosene
• diesel oil
• fuel oil
• bitumen

Question 13

Define fractional distillation

Answer 13

The separation of a liquid mixture into fractions differing in boiling point by means of distillation, typically using a fractionating column

Question 14

What determines what fraction a molecule will go into?

Answer 14

The size and length of the hydrocarbon

Question 15

Explain how the fractional distillation of crude oil works

Answer 15

The different hydrocarbons in crude oil have different boiling points, due to the differing chain lengths. This allows the hydrocarbons to be grouped into fractions of a similar boiling point, allowing for the separation of them

Question 16

What is natural gas used for?

Answer 16

Domestic heating and cooking

Question 17

What is petrol used for?

Answer 17

Fuels for cars

Question 18

What is kerosene used for?

Answer 18

Jet fuel

Question 19

What is diesel used for?

Answer 19

Fuel for some cars and trains

Question 20

What is fuel oil used for?

Answer 20

Ships and power stations

Question 21

What is bitumen used for?

Answer 21

Surfacing roads and roofs

Question 22

What is common in each fraction

Answer 22

• similar properties
• similar boiling points
• similar chain lengths of hydrocarbons

Question 23

Define viscosity

Answer 23

Refers to the ease of the flow of a liquid

Question 24

Why does the boiling point increase as the chain length increases?

Answer 24

As the molecules get larger, the intermolecular forces of attraction between the molecules becomes greater as there is more surface area in contact between them. This means more heat is required to separate the molecules, leading to an increase in boiling point

Question 25

Why does the viscosity increase with chain length?

Answer 25

Due to intermolecular forces of attraction increasing as the molecular size increases

Question 26

Why does the ease of ignition decrease as the chain length increases?

Answer 26

As the molecule size increases, they become harder to ignite as more energy is needed to do so, and therefore the smaller molecules are more flammable

Question 27

Explain why the properties of different fractions differ

Answer 27

Due to the chain length

Question 28

Describe the main features of a homologous series

Answer 28

- same general formula - difference between one molecular formula and the next is CH2 - graduation in their physical properties - same functional group - similar chemical group

Question 29

Why do alkanes form a homologous series?

Answer 29

They have the same general formula and the same functional group, which also means that they differ by CH2 each time

Question 30

Describe the complete combustion of a hydrocarbon

Answer 30

Reaction in which: - only carbon dioxide and water are produced - energy is given out

Question 31

When does incomplete combustion occur?

Answer 31

When there is a limited supply of oxygen

Question 32

What happens during the incomplete combustion of a hydrocarbon?

Answer 32

- water is produced - energy is given out - carbon monoxide and soot are produced

Question 33

State the names of some fossil fuels

Answer 33

- coal - oil - natural gas

Question 34

What is the main hydrocarbon found in crude oil?

Answer 34

Alkanes

Question 35

Why is carbon monoxide a toxic gas?

Answer 35

- it combines with the haemoglobin in red blood cells - which prevents oxygen from combining - this reduces the amount of oxygen carried in the bloodstream - causing suffocation and even death

Question 36

What gases are released through the burning of fossil fuels?

Answer 36

- carbon monoxide - oxides of nitrogen - carbon dioxide - sulfur dioxide

Question 37

What causes acid rain?

Answer 37

Sulfur and nitrogen oxides

Question 38

Describe the effects of acid rain

Answer 38

- causes corrosion to metal structures, buildings and stattues made of carbonate rocks - crops do not grow if soil is too acidic - excess acidity in rivers and lakes prevents fish eggs from hatching, and it can kill fish and insects

Question 39

How is sulfur dioxide formed?

Answer 39

- part of hydrocarbon fuels as impurities, such as petrol and diesel - release when burnt

Question 40

How does sulfur dioxide cause acid rain?

Answer 40

- sulfur dioxide formed from combustion dissolves in rainwater droplets to form sulfuric acid - which then falls with rainwater

Question 41

How are oxides of nitrogen produced?

Answer 41

Formed when nitrogen and oxygen react at high temperatures in internal combustion engines and blast furnaces

Question 42

How do oxides of nitrogen cause acid rain?

Answer 42

- Nitrogen dioxide reacts with rain water to form a mixture of nitrous and nitric acids - which contribute to acid rain - when droplets containing these acids are heavy enough, they will fall as acid rain

Question 43

What are installed in cars to prevent the formation of nitrogen oxides?

Answer 43

Catalytic convertors

Question 44

What is an alternative fuel we can use instead of petrol and diesel?

Answer 44

Hydrogen fuel

Question 45

What are the advantages of using hydrogen fuel?

Answer 45

- releases more energy per kg as compared to other fuels - does not pollute as it only produces water on combustion, no other product is formed

Question 46

What are the disadvantages of using hydrogen fuel?

Answer 46

- expensive and requires energy for the production process - difficult and dangerous to store as it is stored in highly pressurised containers

Question 47

Define **cracking**

Answer 47

Involves breaking covalent bonds in hydrocarbon molecules

Question 48

What are the two types of cracking?

Answer 48

Catalytic cracking and thermal cracking

Question 49

How is cataylitic cracking carried out?

Answer 49

- crude oil fractions are heated to evaporate them - vapours are passed over a catalyst containing aluminium oxides - this breaks the covalent bonds when they come into contact with the surface of the catalyst, causing thermal decomposition reactions - this produces a random selection of alkanes and alkenes

Question 50

How is steam/thermal cracking carried out?

Answer 50

- process carried out similar to catalytic cracking, but at higher temperatures - vapourised hydrocarbons are mixed with steam and heated to a high temperature, which induces cracking

Question 51

Why is cracking necessary?

Answer 51

The demand for certain fractions of crude oil is higher than its supply, so therefore we must convert the surplus unwanted fractions into more useful ones to supply the demand

Question 52

Is cracking an endothermic or exothermic reaction?

Answer 52

Endothermic

Question 53

What are the two hydrocarbons formed by cracking?

Answer 53

An alkane and an alkene

Question 54

What is the difference between a saturated and an unsaturated bond?

Answer 54

- saturated: single bonds between the carbon atoms eg: alkanes - unsaturated: form double bonds between the carbon atoms