Page 72 - Science Coursebook

5.1 Burning

When something burns, a chemical reaction is taking
place. Burning is a chemical reaction in which a substance
combines with oxygen.

In Stage 7 you learnt about different types of energy and

how energy can be changed from one form to another. In a
burning reaction there are energy changes.
The substance that combines with oxygen is called a fuel.
Fuels store energy in the form of chemical energy. Charcoal,
wood, coal, natural gas and oil are examples of fuels.
When you burn a fuel, such as charcoal, for cooking or to
keep warm, heat energy is given out (released). The chemical
energy in the fuel is changed to heat energy and light energy.

Sometimes you can hear the fire burning so you know
that some of the chemical energy is also changed to
sound energy.
Combustion is another term used for burning. Combustion
is often a fast reaction. Combustion of coal.

Reactants and products of combustion

Here is the word equation for the reaction that takes place
when charcoal burns. Charcoal is a form of carbon.

carbon + oxygen → carbon dioxide

There is oxygen in the air around us. About 20% of the air is oxygen. The oxygen is
in the form of oxygen molecules, each made up of two oxygen atoms
bonded together.

When charcoal burns, the oxygen and carbon atoms rearrange themselves and new
bonds are created to form molecules of carbon dioxide. When this rearrangement
happens, energy is given out and the temperature rises.
A chemical reaction in which energy is given out is called an exothermic reaction.

Questions
1 What is needed for combustion to take place?
2 What is an exothermic reaction?
3 How can you tell that burning is an exothermic reaction?

70 5 Energy changes

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