Page 73 - Science Coursebook

5.1 Burning

Burning other substances
Hydrogen can be used as a fuel in a model rocket. string mixture of hydrogen
The combustion of hydrogen is an exothermic reaction. and air
The hydrogen and oxygen combine to form water. paper
hydrogen + oxygen → water clips

When the atoms of hydrogen and oxygen rearrange
themselves and combine together, energy is released. This
chemical energy is changed to kinetic energy, heat energy, stopper
sound energy and light energy. plastic bottle
to spark

In this experiment, a large soda bottle filled with hydrogen generator
and air is attached to a string across the room. The stopper
in the bottle has wires that allow a spark to be generated. Burning hydrogen can propel a plastic
The hot spark provides energy to start the reaction. The bottle like a rocket.
hydrogen and oxygen then react together.

The reaction releases a lot of energy and pushes the stopper out.
This energy makes the bottle shoot (move quickly) along the string.

The reactions of other substances burning in air are also exothermic
reactions. In Stage 8 you burnt magnesium and saw the formation of
magnesium oxide. Energy is given out as heat and light as the
magnesium and oxygen atoms rearrange themselves.
magnesium + oxygen → magnesium oxide

Oxidation reactions Burning magnesium.

When a substance burns, it combines with oxygen and a new
substance called an oxide is formed. Any reaction where a substance combines with
oxygen is also known as an oxidation reaction. Combustion is an oxidation reaction.
When iron rusts, it combines with oxygen from the air. Iron oxide is formed. Although
rusting is a much slower and less vigorous reaction than combustion, it is also an
oxidation reaction.

Questions
4 What sort of reaction is rusting?
5 Which compound is formed when copper reacts with oxygen?
6 When magnesium burns in air what types of energy is the chemical energy
changed into?

Summary
• An exothermic reaction is one in which heat energy is given out.
• Burning (combustion) is an exothermic reaction.
• Burning is a reaction in which a substance combines with oxygen.
• When a substance combines with oxygen, we say that oxidation has taken place.

5 Energy changes 71