Lesson focus: combustionA reaction in which a substance reacts with oxygen, releasing energy as heat and light; it is exothermic and a type of oxidation. transfers energy when a fuelA substance that is burned to release energy, such as petrol or wood. reacts with oxygen, and products depend on the fuel and oxygen supply.
Describe complete and incomplete combustion and evaluate evidence about products and hazards.
Build on earlier learning
Word equationsWord-equation patterns now describe burning reactions.
Practical
What burning produces
- Watch a teacher burn a fuel under an upturned funnel connected to a cooled tube and limewater.
- Water collects in the cooled tube; limewater turns cloudy.
- Compare a yellow, sooty flame with a clean blue flame.
Record: Observations and the products they show (water and carbon dioxide).
Safety: Demonstration only.
You will be successful when you can…
- Define combustion and fuel.
- Write a general combustion equation.
- Distinguish complete and incomplete combustion.
- Explain carbon monoxide risk.
Words that carry the science
- combustion
- A reaction with oxygen that transfers energy to the surroundings.
- fuel
- A substance used to release energy in a reaction.
- oxidation
- A reaction involving gain of oxygen at this level.
- complete combustion
- Combustion with sufficient oxygen.
- carbon monoxide
- A toxic, colourless gas formed by incomplete combustion of carbon-containing fuels.
Combustion is reaction with oxygen
01Combustion is reaction with oxygen
Burning is combustionA reaction in which a substance reacts with oxygen, releasing energy as heat and light; it is exothermic and a type of oxidation.. The fuelA substance that is burned to release energy, such as petrol or wood. reacts with oxygen and usually transfers energy by heating and light.
For a hydrocarbon fuel, complete combustionBurning a fuel in plenty of oxygen; a fuel made of carbon and hydrogen then makes only carbon dioxide and water. forms carbon dioxide and water. Other fuels can contain different elements and form different oxides.
02Oxygen supply changes products
With insufficient oxygen, carbon-containing fuels can undergo incomplete combustionA reaction in which a substance reacts with oxygen, releasing energy as heat and light; it is exothermic and a type of oxidation., forming carbon monoxideA poisonous gas with no colour or smell, made when fuels burn without enough oxygen. and/or soot as well as water.
A yellow smoky flame can indicate incomplete combustion, while a well-mixed blue flame often indicates more complete combustion. Flame colour alone is not a gas test.
03Product tests and ventilation matter
Carbon dioxide turns limewater cloudy; water can turn blue cobalt chloride paper pink. These tests require control experiments and careful handling.
Carbon monoxide interferes with oxygen transport in blood. It cannot be seen or smelled, so appliances need correct ventilation and maintenance.
Combustion: burning fuels
Burning (combustion) is a reaction with oxygen. A hydrocarbon fuel such as methane burns to make carbon dioxide and water. The atoms are rearranged: none are made or destroyed, so mass is conserved.
Black: carbon. Red: oxygen. White: hydrogen.
Controls
Test for carbon dioxide: it turns limewater milky. Test for water: it turns blue cobalt chloride paper pink.
Explain a yellow gas flame
A burner produces a yellow, sooty flame.
- The fuel is reacting with oxygen.
- Air mixing is insufficient for complete combustion.
- Carbon particles form and glow yellow before depositing as soot.
- Carbon monoxide may also form, so ventilation and burner adjustment matter.
How to make the reasoning visible: The observations support incomplete combustion, but do not quantify each gas product.
Combustion evidence demonstration
Use the evidence from each condition to identify the products of burning.
| Condition | Flame | Deposit | Gas evidence |
|---|---|---|---|
| open air hole | blue | little soot | CO₂ + water |
| closed air hole | yellow | black soot | possible CO |
| candle under jar | dims then stops | possible soot | oxygen falls |
| magnesium in oxygen | bright white | white solid | magnesium oxide |
Which examples show why one product pattern cannot cover every fuel?
Why is the closed-air-hole condition hazardous?
Check your understanding
Answer from memory, then check against the suggested answer.
What is combustion?
Products of complete hydrocarbon combustion?
Name one incomplete product.
Why must a gas heater have an adequate air supply?
Why can mass increase when magnesium burns?
Exam Question Practice
Exam Question Practice
Mark points shown after marking
A carbon-fuel heater is used in a room with poor ventilation.
Explain what happens to the combustion of the fuel.
(3)Explain why carbon monoxide is dangerous.
(2)Total for this question: 5 marks
Command word: For explainA command word: say how or why something happens, giving reasons with words like "because" or "so"., link the environmental condition to chemistry and then to harm.