WACE Chemistry — Unit 3
Hydrocarbons — Flashcards & Quiz
Hydrocarbons are compounds of carbon and hydrogen only, and WACE Chemistry Year 12 expects you to distinguish alkanes, alkenes and alkynes by their bonding, predict reactions, and use IUPAC nomenclature to name and draw structures. Combustion equations and Markovnikov's rule for alkene addition are high-yield exam content.
Key Points
- Alkanes (CₙH₂ₙ₊₂): saturated, single bonds only, react by substitution with halogens under UV light.
- Alkenes (CₙH₂ₙ): at least one C=C double bond, react by addition (Br₂, H₂, H₂O, HX) breaking the π bond.
- Alkynes (CₙH₂ₙ₋₂): at least one C≡C triple bond, also react by addition.
- Combustion: complete combustion in excess O₂ gives CO₂ + H₂O; incomplete gives CO and/or soot.
- Isomerism: structural (different connectivity) or geometric (cis/trans in alkenes with two different groups on each C=C carbon).
- IUPAC naming: longest chain containing the functional group, number to give lowest locants, alphabetise substituents.
Common Mistakes to Avoid
- Confusing alkanes (substitution) with alkenes (addition).
- Writing incomplete combustion as CO₂ only — incomplete gives CO and/or carbon soot.
- Forgetting that alkanes don't decolourise bromine water without UV light, but alkenes do.
- Missing cis/trans isomerism in alkenes with identical groups on the same side.
- Using common names instead of IUPAC in formal exam responses.
Exam Strategy
SCSA Unit 3 hydrocarbon questions ask you to name structures, predict reaction products, or balance combustion equations. Method: (1) identify the hydrocarbon type, (2) match to the characteristic reaction, (3) write and balance the equation with catalysts/conditions, (4) apply IUPAC naming rules to products.
Revision Tip
Hydrocarbon reactions are pattern-based — build a Revizi deck with 3-4 reactions per hydrocarbon type (combustion, substitution, addition) for fluency.
Related Concepts
Last updated: March 2026