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Most of the compounds in crude oil are hydrocarbons.

Chemistry - Hydrocarbons and Fuels (AQA)

Hydrocarbons are key chemicals in fuels. In GCSE Chemistry you learn how their structure affects properties like burning, viscosity and everyday uses from car petrol to heating.

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Fascinating Fact:

Long chain hydrocarbons are viscous and hard to ignite. They are used as lubricants and bitumen.

In GCSE Science (Chemistry), you study hydrocarbons as the main ingredients of fossil fuels. You learn how chain length alters boiling point, flammability and viscosity, and why different fuels suit different jobs.

Key Terms

Hydrocarbon: A compound made only from hydrogen and carbon atoms, found in fuels like petrol, diesel and bottled gas.
Fossil fuel: A fuel such as coal, oil or gas, formed from dead organisms over millions of years under heat and pressure.
Viscosity: A measure of how easily a liquid flows, with high-viscosity liquids being thick and slow moving.

Frequently Asked Questions (Click to see answers)

What is a hydrocarbon in GCSE Chemistry?

In GCSE Chemistry, a hydrocarbon is defined as a compound containing only hydrogen and carbon atoms. Crude oil and natural gas are important natural mixtures of hydrocarbons.

How does chain length affect hydrocarbon properties?

As chain length increases, hydrocarbons usually have higher boiling points, become thicker liquids and are often less flammable. Shorter chains tend to be more volatile and easier to ignite.

What are the products of complete combustion of a hydrocarbon?

In complete combustion, a hydrocarbon reacts with plenty of oxygen to form carbon dioxide and water, releasing energy as heat. This is the ideal process in a well-maintained burner.

Try These Related Quizzes

1 .

During the combustion of hydrocarbons, what happens to the carbon and hydrogen atoms?

They change into new elements

They are destroyed completely

They are reduced

They are oxidised

All combustion reactions involve oxidation of the atoms of the fuel

2 .

Which of the following is an alkane?

C₂H₂

C₄H₆

C₆H₁₂

C₈H₁₈

Testing to see if you know that the general formula for alkanes is C_nH_2n+2 where n is the number of carbon atoms in the hydrocarbon

3 .

What is a hydrocarbon?

A compound containing only hydrogen and carbon

A compound containing mainly hydrogen and carbon

A compound containing only hydrogen, carbon and oxygen

The only type of chemical that we ever use as a fuel

It's all in the name! Although hydrocarbons are probably the most important fuel we use, they are by no means the only one

4 .

Which of the following is not a product of burning hydrocarbons as fuels?

Carbon monoxide

Water vapour

Oxygen

Carbon dioxide

Oxygen is required for burning hydrocarbons as fuels

5 .

Some properties of hydrocarbons depend on the size of their molecules. These properties influence how hydrocarbons are used as fuels. A hydrocarbon with 30 carbon atoms is unlikely to be used as a fuel in vehicles. Why not?

Because it is a solid

Because it is a liquid

Because it is a gas

Because it is not possible to burn it

Liquids are the only practical fuels for vehicles

6 .

When we use hydrocarbons as fuels they produce particulates (small particles of solids e.g. soot). What environmental problem is caused by the release of these solids?

Global dimming

Global warming

Acid rain

Ozone depletion

They block some of the Sun's rays from reaching the surface of the Earth

7 .

Which of these is the correct equation for the complete combustion of propane?

CH₄ + 2O₂ → CO₂ + H₂O

2C₂H₄ + 6O₂ → 2CO₂ + 2H₂O

C₃H₈ + 5O₂ → 3CO₂ + 4H₂O

2C₃H₈ + 7O₂ → 6CO + 8H₂O

You should have immediately dismissed the first two as they are not propane. The third and fourth answers are correctly balanced equations for propane but the fourth one shows the incomplete combustion of propane

8 .

There are environmental costs when using hydrocarbons as fuels. Using them in this way produces a number of pollutants. Which one of the following contributes to acid rain?

Carbon monoxide

Carbon dioxide

Methane

Sulfur dioxide

Whilst carbon dioxide does make rainwater slightly acidic, it is the sulfur dioxide (and nitrogen oxides) that takes the pH below 6, creating the acid rain

9 .

Soot is mainly particles of what?

Unburned hydrocarbons

Sulfur

Carbon

Solidified nitrogen oxides

Soot is a product of the incomplete combustion of hydrocarbons

10 .

16g of methane required 64g of oxygen to burn completely producing 44g of carbon dioxide. How many grams of water were produced?

The examiners could throw something like this at you in any question in order to test your knowledge of the law of conservation of mass in chemical reactions. To get the right answer, you only need to be able to add and subtract! Work out how many grams of chemical that you started with then look how many are missing at the end. That is your answer

You can find more about this topic by visiting BBC Bitesize - Crude oil, hydrocarbons and alkanes - AQA

Author: Kev Woodward (PGCE, Science & Chemistry Teacher, Quiz Writer)