Combustion of Alkenes
- These compounds undergo complete and incomplete combustion but because of the higher carbon to hydrogen ratio they tend to undergo incomplete combustion, producing a smoky flame in air.
- Complete combustion occurs when there is excess oxygen so water and carbon dioxide form e.g:
C4H8 + 6O2 → 4CO2 + 4H2O
butene + oxygen → carbon dioxide + water
- Incomplete combustion occurs when there is insufficient oxygen to burn so a mixture of products can form, e.g:
C4H8 + 4O2 → 4CO + 4H2O
butene + oxygen → carbon monoxide + water
- In addition to carbon monoxide, carbon in the form of soot can be produced:
C4H8 + 2O2 → 4C + 4H2O
butene + oxygen → carbon + water
- This is more likely to occur in higher alkenes with larger number of carbons
- This is seen as smoky yellow flames when the alkenes burn
Smoky flames indicates a higher carbon to hydrogen ratio in organic molecules, such as alkenes.