Topic 8 - Fuels And Earth Science

Question 1

What are hydrocarbons?

Answer 1

Compounds that contain hydrogen and carbon atoms only.

Question 2

What is crude oil?

Answer 2

A complex mixture of hydrocarbons
Contains molecules with rings or chains of carbon atoms
An important source of useful substances like fuels and feedstocks for the petrochemical industry
A finite resource

Question 3

Where can crude oil be found?

Answer 3

Under the sea and ground

Question 4

What does it mean when crude oil is described as “finite”?

Answer 4

It will run out.

Question 5

How can crude oil be separated?

Answer 5

Fractional distillation

Question 6

How does the process of fractional distillation work to separate crude oil?

Answer 6

Crude oil is vaporised before it enters a fractionating column.
The fractionating column is hotter at the bottom than at the top. The vapours rise up and condense at different fractions depending on their boiling points.
Hydrocarbons with low boiling points will be tapped off the top of the column and hydrocarbons with high boiling points will be tapped off the bottom of the column.

Question 7

Why is crude oil separated?

Answer 7

Unseparated crude oil isn’t very useful but the separated products (such as petrol) are very useful.

Question 8

Refinery gas is a fraction of crude oil. What are its common uses?

Answer 8

Heating and cooking.

Question 9

Which fraction of crude oil is used as fuel in cars?

Answer 9

Petrol (gasoline)

Diesel is also less commonly used.

Question 10

Kerosene is a fraction of crude oil. What is a common use of kerosene?

Answer 10

Aircraft fuel.

Question 11

Diesel oil is fraction of crude oil. What is it commonly used for?

Answer 11

Fuel for some cars and trains.

Question 12

Which fraction of crude oil is used for road surfacing and roofs?

Answer 12

Bitumen

Question 13

Fuel oil is fraction of crude oil. What is it commonly used for?

Answer 13

Fuel for large ships and in some power stations.

Question 14

How do hydrocarbons at each faction differ?

Answer 14

Boiling points
Ease of ignition
Viscosity
The number of hydrogen and carbon atoms their molecules have

Question 15

Where in the fractionating column do hydrocarbons with the highest viscosity condense?

Answer 15

Viscosity is how thick and sticky a substance is.
The hydrocarbons with the highest viscosity (like bitumen) are collected at the bottom of the fractionating column.

Question 16

What are the properties of hydrocarbons that are tapped from the top of the fractionating column, like petrol and refinery gas?

Answer 16

Low boiling point
Highly volatile
Easily ignited
Shorter carbon chains (small molecules)

Question 17

What is a homologous series?

Answer 17

Series of compounds which:
have the same general formula
Have similar chemical properties
Differ by CH2 (subscript) in molecular formula form neighbouring molecules.
Slight variation in physical properties.

Question 18

Products from crude oil mostly belong to which homologous series?

Answer 18

Alkane homologous series

Question 19

What are the only products when a hydrocarbons fuel undergoes complete combustion?

Answer 19

Water (H20) and carbon dioxide (CO2)

Question 20

True or false?
Energy is given out when a fuel undergoes complete combustion?

Answer 20

True
The reaction is exothermic.

Question 21

Write a balanced symbol equation for the complete combustion of ethane

Answer 21

2C2(subscript)H6(subscript) + 7O2(subscript) arrow 4CO2 (subscript) + 6H2 (subscript)O

Question 22

When does incomplete combustion occur? What is required to ensure complete combustion occurs?

Answer 22

Incomplete combustion occurs when there is an insufficient supply of oxygen.
To ensure complete combustion occurs, the reaction should be carried out with excess oxygen.

Question 23

What are the products of incomplete combustion?

Answer 23

Carbon particulates - soot (C)
Carbon monoxide (CO)
Water (H20)

Question 24

Write a balanced symbol equation for the incomplete combustion of methane to form carbon monoxide

Answer 24

2CH4 (subscript) 3O2 (subscript) arrow 2CO + 4H2 (subscript) O

Question 25

Write a balanced symbol equation for the incomplete combustion of methane to form carbon particulates

Answer 25

CH4 (subscript) + O2 (subscript) arrow C + 2H2O (2 subscript)

Question 26

What are the problems with carbon monoxide?

Answer 26

Carbon monoxide is a toxic gas
It is colourless and odourless and if breathed in can cause death by preventing the red blood cells from carrying oxygen around the body.

Question 27

What are the problems with incomplete combustion?

Answer 27

Produces carbon monoxide which is toxic and can be fatal if breathed in.
Produces carbon particulates (soot) which cause global dimming and respiratory problems.

Question 28

Why is sulfur dioxide sometimes produced when burning hydrocarbon fuels?

Answer 28

Some hydrocarbon fuels contain sulfur impurities. When the fuel is burned, the sulfur reacts with oxygen to form sulfur dioxide.

Question 29

How is acid rain produced?

Answer 29

Sulfur dioxide (produced when combusting impure hydrocarbon fuels) evaporates into the air. It reacts with water in the clouds to form sulfuric acid. This is acid rain.

Question 30

What problems can acid rain cause?

Answer 30

Corrodes buildings and statues made of limestone.
Kills/damages the vegetation.
Lower the pH of large bodies of water, killing the wildlife.

Question 31

How are oxides of nitrogen produced from car engines?

Answer 31

The high temperature and pressure of a car engine causes nitrogen and oxygen from the air to react together.

Question 32

What problems are associated with oxides of nitrogen?

Answer 32

Pollutants.
Produce acid rain with similar effects as SO2 (subscript)
Cause respiratory problems.

Question 33

What are the advantages of using hydrogen as a fuel in cars?

Answer 33

It releases more energy per kg compared to most other fuels.
Water is the only product so no pollutants.
Renewable source of hydrogen can be extracted from water.

Question 34

What are the disadvantages of using hydrogen as a fuel in cars?

Answer 34

It is expensive to produce and a lot of energy is required for the electrolysis of water to acquire the hydrogen.
Difficult and dangerous to store hydrogen because it is very volatile and easily ignites.

Question 35

Name the non-renewable fossil fuel found in natural gas

Answer 35

Methane

Question 36

Are petrol, kerosene and diesel renewable fuels?

Answer 36

No, they are non-renewable.
They are finite resources which are not being readily replaced.

Question 37

What is cracking?

Answer 37

Breaking down large hydrocarbons into smaller more useful ones.
Saturated alkanes are cracked into shorter chain alkanes and short chain unsaturated alkenes.

Question 38

What do the terms saturated and unsaturated mean?

Answer 38

Saturated - only contains single bonds
Unsaturated - contains some C=C double bonds

Question 39

What type of reaction is cracking?

Answer 39

Thermal decomposition

Question 40

Why is cracking necessary?

Answer 40

The demand for shorter chain alkenes and alkanes is much greater than the demand for long chain alkanes.

Question 41

What produced the gases that formed Earth’s early atmosphere?

Answer 41

Volcanic activity

Question 42

Describe how Earth’s early atmosphere formed

Answer 42

Initially the Earth’s surface was molten with no atmosphere
Cooling caused land masses to solidify
Volcanoes formed on the land masses and released gases which formed the early atmosphere.

Question 43

What was the Earth’s early atmosphere thought to contain?

Answer 43

Little or no oxygen
Large amount of carbon dioxide
Water vapour
Small amounts of other gases