Alkanes & Alkenes
Year 10 (IGCSE) 🌿 Materials & Environment Compare saturated and unsaturated hydrocarbons; describe key reactions.
🔗 Alkanes (Saturated)
Alkanes contain only C-C single bonds. General formula CₙH₂ₙ₊₂. They are relatively unreactive — undergo combustion and substitution only.
Substitution with Cl₂ (in UV): CH₄ + Cl₂ → CH₃Cl + HCl (free radical mechanism).
🔗 Alkenes (Unsaturated)
Alkenes have at least one C=C double bond. General formula CₙH₂ₙ. More reactive — undergo addition reactions.
Test: Add bromine water — alkenes decolourise it (orange → colourless). Alkanes do not.
Reaction: CH₂=CH₂ + Br₂ → CH₂BrCH₂Br (1,2-dibromoethane)
🧪 Addition Reactions of Alkenes
Hydrogenation: CH₂=CH₂ + H₂ → CH₃CH₃ (Ni cat, 150°C) — making margarine.
Hydration: CH₂=CH₂ + H₂O → CH₃CH₂OH (ethanol) at 300°C, H₃PO₄ cat.
Addition polymerisation: n(CH₂=CH₂) → (–CH₂–CH₂–)ₙ
Hydration: CH₂=CH₂ + H₂O → CH₃CH₂OH (ethanol) at 300°C, H₃PO₄ cat.
Addition polymerisation: n(CH₂=CH₂) → (–CH₂–CH₂–)ₙ
Ready to test yourself? Click the Quiz tab above to practise questions on this topic!
Interactive Demonstration — Alkanes & Alkenes
Compare alkanes (saturated) and alkenes (unsaturated). Test with bromine water.
🔗 Alkane/Alkene Formula Calculator
Calculate CO₂ and H₂O produced in complete combustion.