1The fire triangle
Combustion needs fuel, heat and oxygen: the fire triangle. Take any one away and the fire goes out.
combustionfire triangle
Lesson 11.2 notes
Combustion and oxidation
The fire triangle, what burning fuels make, metals gaining oxygen, and rusting.
2Burning uses oxygen
A candle under a jar goes out when there is too little oxygen left. Combustion is a reaction with oxygen.
oxygen
3What burning makes
Most fuels contain carbon and hydrogen. Burning makes carbon dioxide, which turns limewater cloudy, and water, which turns cobalt chloride paper pink.
carbon dioxidewater
4Not enough oxygen
With the air hole open, the gas burns completely: a blue flame. With too little air, it makes soot and poisonous carbon monoxide: a yellow, sooty flame.
incomplete combustioncarbon monoxide
5Oxidation
When a substance gains oxygen it is oxidised. Copper heated in air turns into black copper oxide, and gets heavier.
oxidationoxide
6Rusting
Rusting is the slow oxidation of iron. It needs both oxygen (from the air) and water.
rusting
7Stopping rust
Paint, oil, grease or a coat of zinc (galvanising) keeps air and water away from iron, so it can't rust.
galvanising
Explore: Fire triangle
Take away the fuel, the heat or the oxygen, and see what happens to the fire.
Common mistake: Burning does not destroy the fuel's atoms
A candle seems to disappear, but its atoms have joined with oxygen to make carbon dioxide and water vapour, which escape into the air. Trapped, the products would weigh more than the wax.
Remember
- Combustion: fuel + oxygen → oxides, giving out heat and light. A fire needs fuel, heat and oxygen.
- Fuels with carbon and hydrogen make carbon dioxide (limewater turns cloudy) and water (cobalt chloride paper turns pink).
- Oxidation means gaining oxygen. Iron rusts only when it has both oxygen and water.
Going further at GCSE
GCSE: Complete combustion → GCSE: Pollutants from burning fuels → GCSE: Metal oxides →