This exam tips covers Exam Tips: Combustion within Combustion for GCSE Chemistry. Revise Combustion in Organic Chemistry for GCSE Chemistry with 25 exam-style questions and 15 flashcards. Use this page as part of a wider topic revision path rather than treating it as an isolated fact. It is section 12 of 13 in this topic. Treat this as a marking guide for what examiners are looking for, not just a fact list.
💡 Exam Tips: Combustion
🎯 Common Question Types:
- Balance a combustion equation (2-3 marks)
- Compare complete and incomplete combustion (3-4 marks)
- Explain why CO is dangerous (2 marks)
- Suggest why a gas appliance has a yellow flame (1-2 marks)
📝 Key Command Words:
- Balance: Balance C, then H, then O. Check atom counts
- Compare: State differences in products, flame colour, energy
- Explain: Link CO to haemoglobin and oxygen transport
⚠️ Common Mistakes to Avoid:
- Forgetting soot/carbon as a possible product
- Saying ONLY CO₂ and H₂O are produced in incomplete combustion — incomplete combustion produces CO and/or carbon (soot) in addition to or instead of CO₂
- Forgetting state symbols in 6-mark questions
Quick Check: Write the balanced equation for the complete combustion of ethane (C₂H₆).
C₂H₆(g) + 3½O₂(g) → 2CO₂(g) + 3H₂O(l) OR: 2C₂H₆(g) + 7O₂(g) → 4CO₂(g) + 6H₂O(l). Step-by-step: 2 carbons → 2CO₂; 6 hydrogens → 3H₂O; oxygens needed = (2×2)+(3×1) = 7 → 3.5O₂ (or multiply through by 2).
Quick Check: A gas fire in a room with poor ventilation begins to produce a yellow flame. Suggest two risks this creates.
1. Carbon monoxide (CO) is produced — a colourless, odourless toxic gas that binds to haemoglobin and prevents oxygen transport, potentially causing death. 2. Soot/carbon particles are released into the air, causing respiratory problems and settling on surfaces.
Practice questions for Combustion
What are the only products formed during the complete combustion of a hydrocarbon?
Explain why carbon monoxide (CO) is toxic to humans. [3 marks]