Types of Chemical Reaction
Identify and describe four types of chemical reaction: combustion (burning in oxygen), oxidation (gain of oxygen), thermal decomposition (breaking down by heat), and displacement (more reactive metal replaces less reactive one)
What a learner can do afterwards
- Writes a word equation for each type of reaction with an example
- Identifies the type of reaction from a given word equation or description
- Explains what makes a displacement reaction happen (relative reactivity)
- Distinguishes complete combustion (CO₂ and H₂O) from incomplete combustion (CO and soot)
The lesson
A chemical reaction makes a new substance that you can't turn back into the old one. Scientists group common reactions by what happens to the atoms inside them. Four groups you'll meet again and again are combustion, oxidation, thermal decomposition, and displacement.
When a candle burns, the wax reacts with oxygen in the air. This is combustion: a substance burning in oxygen. Word equation: wax + oxygen → carbon dioxide + water. With plenty of oxygen, combustion is complete, and you get carbon dioxide and water, like a clean flame. With too little oxygen, combustion is incomplete, and you get carbon monoxide and soot instead, like a smoky, sooty flame.
Rusting is a slower reaction called oxidation: a substance gains oxygen. Iron reacts slowly with oxygen in damp air and forms iron oxide, the orange-brown coating we call rust. Word equation: iron + oxygen → iron oxide. Oxidation doesn't need a flame. It just needs time, oxygen, and usually some water.
Thermal decomposition works the opposite way. Instead of substances joining, one substance breaks apart when it's heated. Heating calcium carbonate (limestone) in a kiln splits it into calcium oxide and carbon dioxide gas. Word equation: calcium carbonate → calcium oxide + carbon dioxide. The clue is that decomposition starts with only one substance.
In a displacement reaction, a more reactive metal pushes a less reactive metal out of its compound. Drop an iron nail into blue copper sulfate solution, and the blue fades as iron takes copper's place, leaving a coating of copper on the nail. Word equation: iron + copper sulfate → iron sulfate + copper. This only works because iron is more reactive than copper. A less reactive metal could never displace iron this way.
Spot the type: burning in oxygen is combustion, a slow gain of oxygen is oxidation, heat splitting one substance apart is decomposition, and a reactive metal swap is displacement.
Watch it
Where it sits
Where this leads
Jobs that lean on this skill. Follow one to see everything it is built on.
8 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.