Propane undergoes complete combustion. Explain what is meant by complete combustion and describe the environmental problems caused by the products of this reaction.
Written & reviewed by James Millett — Biology (Imperial College London), PGCE Science (University of Cambridge).
Propane (C₃H₈) is a hydrocarbon fuel used in gas-powered barbecues and central heating systems. It is a non-renewable fossil fuel.
Model answer (5 marks)
Complete combustion means that all the carbon in the fuel reacts with sufficient oxygen to give only carbon dioxide and water.
In the combustion of propane:
C3H8 + 5O2 → 3CO2 + 4H2O
The CO2 released is a greenhouse gas; it traps heat in the atmosphere and contributes to the greenhouse effect. The additional CO2 increases the atmospheric concentration of greenhouse gases, leading to climate change and higher global temperatures. The water vapour produced is also a greenhouse gas, and burning a fossil fuel releases CO2 that was previously stored underground, further raising atmospheric CO2 levels.
In the combustion of propane:
C3H8 + 5O2 → 3CO2 + 4H2O
The CO2 released is a greenhouse gas; it traps heat in the atmosphere and contributes to the greenhouse effect. The additional CO2 increases the atmospheric concentration of greenhouse gases, leading to climate change and higher global temperatures. The water vapour produced is also a greenhouse gas, and burning a fossil fuel releases CO2 that was previously stored underground, further raising atmospheric CO2 levels.
Examiner tips
- Define complete combustion and give the balanced equation
- State the products CO2 and H2O
- Explain CO2 as a greenhouse gas and link to climate change
- Mention water vapour and fossil‑fuel CO2 release
Common mistakes
- Confusing incomplete with complete combustion
- Saying only CO2 is released and ignoring H2O
- Not linking CO2 to greenhouse effect
Mark scheme (5 marks)
- Complete combustion requires sufficient oxygen
- The only products of complete combustion of a hydrocarbon are carbon dioxide and water
- Carbon dioxide is a greenhouse gas that contributes to the greenhouse effect
- Increased carbon dioxide concentration leads to climate change / increased global temperatures
- Water vapour produced is itself a greenhouse gas OR burning propane as a fossil fuel releases CO₂ previously locked away, increasing atmospheric concentration
Key terms in this question
Related
- All Edexcel A-Level Chemistry (9CH0) revision notes →
- How to answer a "Explain and Describe" question →
- Decode the mark scheme abbreviations →
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