Alkanes
Section: Chemistry | Syllabus: Cambridge IGCSE Combined Science (0653)
Alkanes
The bonding in alkanes is single covalent throughout, so alkanes are saturated hydrocarbons.
| Name | Molecular formula | Structural formula |
|---|---|---|
| Methane | CH₄ | CH₄ |
| Ethane | C₂H₆ | CH₃CH₃ |
| Propane | C₃H₈ | CH₃CH₂CH₃ |
| Butane | C₄H₁₀ | CH₃CH₂CH₂CH₃ |
Reactivity of Alkanes
Alkanes are generally unreactive, because the C-C and C-H single bonds are strong. The one reaction they readily undergo is combustion.
Combustion
- Complete combustion (plenty of oxygen): alkane + oxygen → carbon dioxide + water
- Incomplete combustion (limited oxygen): produces carbon monoxide and/or carbon (soot) instead of carbon dioxide
Worked Example
- Question (based on a real exam question): name two substances produced when ethane undergoes complete combustion. [2]
- Answer: carbon dioxide and water [2]. C₂H₆ + 3½O₂ → 2CO₂ + 3H₂O.
Common Mistakes
- ❌ Thinking alkanes are highly reactive, like alkenes
- ✓ alkanes are generally unreactive because their C-C and C-H single bonds are strong - combustion is the main reaction they undergo
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