Year 8 · Science · Chemical reactions · Lesson 2

Combustion

Combustion of fuels, word equations for complete combustion, incomplete combustion and carbon monoxide, the fire triangle, and the tests for the products.

24-minute video lesson

Teaching, worked examples and 20 practice questions solved step by step.

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What your child will learn

Describe combustion as a reaction with oxygen
Write word equations for complete combustion
Explain incomplete combustion and its dangers
Use the fire triangle to explain how fires are put out
Describe tests for carbon dioxide and water

The method

Combustion is a fuel reacting with oxygen, releasing heat and light (exothermic, oxidation).
Complete combustion of a hydrocarbon: fuel + oxygen → carbon dioxide + water.
Incomplete combustion (too little oxygen) makes carbon monoxide and soot.
A fire needs fuel, heat and oxygen; remove one to put it out.

Key words: combustion, fuel, hydrocarbon, oxidation, fire triangle, carbon monoxide, incomplete combustion, exothermic.

Worked examples

The first three practice questions from the lesson, with every step.

Question 1

Write the word equation for the complete combustion of propane.

Step 1: propane + oxygen
Step 2: → carbon dioxide + water

Answer: propane + oxygen → carbon dioxide + water

Question 2

Write the word equation for the complete combustion of butane.

Step 1: butane + oxygen
Step 2: → carbon dioxide + water

Answer: butane + oxygen → carbon dioxide + water

Question 3

Why is combustion an exothermic reaction?

Step 1: It gives out heat (and light)

Answer: It gives out heat