Key Terms
- Complete combustion — excess O₂, produces CO₂ + H₂O
- Incomplete combustion — limited O₂, produces CO and/or C
- Carbon monoxide — toxic, colourless, odourless
Complete vs Incomplete
- Complete: blue flame, CO₂ + H₂O, max energy
- Incomplete: yellow flame, CO/C, less energy
- CO binds haemoglobin → prevents O₂ transport
Balancing Equations
- Balance C first → CO₂ count
- Balance H next → H₂O count
- Balance O last → O₂ count
- Check all atoms on both sides
Exam Checklist
- State symbols: CO₂(g), H₂O(l), C(s), CO(g)
- CO = colourless, odourless, toxic
- Yellow flame = incomplete combustion
- Complete = more energy released
Key Equations
- CH₄ + 2O₂ → CO₂ + 2H₂O (complete combustion of methane)
- 2CH₄ + 3O₂ → 2CO + 4H₂O (incomplete combustion — CO)
- CH₄ + O₂ → C + 2H₂O (incomplete combustion — soot/carbon)
Common Mistakes
- Saying incomplete combustion produces CO₂: Incomplete combustion produces carbon MONOXIDE (CO) and/or carbon soot — NOT CO₂
- Forgetting water is always produced in combustion: Both complete AND incomplete combustion of hydrocarbons always produce water — hydrogen atoms in the fuel always bond with oxygen
- Not knowing CO is toxic: Carbon monoxide binds irreversibly to haemoglobin, preventing oxygen transport — it is colourless and odourless (impossible to detect without equipment)
- Saying complete combustion produces more products: Complete combustion actually produces FEWER types of products (only CO₂ and H₂O) but releases MORE energy than incomplete combustion
This topic summary covers Knowledge Organiser: Combustion of Hydrocarbons 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 13 of 13 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
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]
Quick recall flashcards
What is combustion?
Combustion is the reaction of a substance with oxygen, releasing energy as heat and light (burning)
What is complete combustion?
Complete combustion occurs when there is plenty of oxygen, producing only carbon dioxide (CO₂) and water (H₂O)