This topic summary covers Topic Summary: Alkenes within Alkenes for GCSE Chemistry. Revise Alkenes in Organic Chemistry for GCSE Chemistry with 20 exam-style questions and 15 flashcards. This is a high-frequency topic, so it is worth revising until the explanation feels precise and repeatable. It is section 14 of 14 in this topic. Use this topic summary to connect the idea to the wider topic before moving on to questions and flashcards.
Topic position
Section 14 of 14
Practice
20 questions
Recall
15 flashcards
Topic Summary: Alkenes
Key Terms
- Alkene — unsaturated hydrocarbon, CₙH₂ₙ
- Unsaturated — contains C=C double bond
- Addition reaction — atoms add across C=C
- Decolourisation — bromine water turns colourless
First Four Alkenes
- Ethene — C₂H₄
- Propene — C₃H₆
- Butene — C₄H₈
- Pentene — C₅H₁₀
Addition Reactions
- + H₂ → alkane (Ni catalyst, 150°C)
- + Br₂ → dibromoalkane (test)
- + H₂O → alcohol (H₃PO₄, 300°C, 70 atm)
Exam Checklist
- CₙH₂ₙ formula (not CₙH₂ₙ₊₂)
- Bromine water: say "decolourised"
- Unsaturated = C=C double bond
- Source of alkenes: cracking