Chemistry • Year 12 • Module 7 • Lesson 8
Hydrocarbon Reactions Mastery
Recall and organise the complete set of hydrocarbon reaction conditions — reagents, catalysts, temperatures and pressures — for combustion, free-radical substitution, addition and polymerisation.
1. Complete the hydrocarbon reactions reference table
Fill in every blank cell. Use the lesson's Conditions Table (L05–L07) as your source. Abbreviations: r.t. = room temperature; atm = atmospheres. 18 marks (1 per correct cell)
| Reaction | Reaction type | Reagent(s) | Catalyst / initiator | Conditions (T, P) | Main organic product |
|---|---|---|---|---|---|
| Alkane + O2 (excess) | O2 (excess) | ignition | |||
| Alkane + Cl2 / Br2 | r.t.; UV light | ||||
| Alkene + H2 | H2 | 150–200 °C; high P | |||
| Alkene + Br2 | Br2 (aq or CCl4) | none | |||
| Alkene + HX | none | r.t. | haloalkane (Markovnikov product) | ||
| Alkene + H2O | H2O (steam) | ~300 °C; ~65 atm | |||
| Alkyne + H2 (2 eq) | H2 (excess) | Ni, Pd or Pt | |||
| Alkyne + H2 (1 eq) | partial hydrogenation | H2 (1 eq) | mild; low T | ||
| Alkyne + HX (1 eq) | HX (1 eq) | none | vinyl halide (Markovnikov) | ||
| Alkyne + HX (2 eq) | two-step hydrohalogenation | none | r.t. | ||
| Alkyne + H2O | H2O | ~60 °C | |||
| Alkene polymerisation | monomer (alkene) | initiator (peroxide) |
2. Term–definition match
Match each term to the correct definition. Write the letter in the right-hand column. 8 marks
Terms: A – vicinal dihalide • B – geminal dihalide • C – Markovnikov’s rule • D – hydration • E – hydrogenation • F – free-radical substitution • G – Lindlar catalyst • H – enol tautomerisation
| # | Definition | Your answer (A–H) |
|---|---|---|
| 2.1 | The addition of water across a double or triple bond, requiring an acid catalyst. | |
| 2.2 | A compound with both halogen atoms on the same carbon atom. | |
| 2.3 | A poisoned palladium catalyst that stops hydrogenation at the alkene stage. | |
| 2.4 | The process by which an unstable enol intermediate converts to a ketone. | |
| 2.5 | In addition of HX to an unsymmetrical alkene, H attaches to the carbon already bonded to more hydrogen atoms. | |
| 2.6 | A compound with halogen atoms on two adjacent carbons, formed by halogenation of an alkene. | |
| 2.7 | A chain reaction initiated by UV light where a halogen atom replaces an H on an alkane. | |
| 2.8 | The addition of H2 across a multiple bond using a metal catalyst. |
3. True or false — with correction
Circle T or F. If false, write the correct version on the line. 8 marks (1 T/F + 1 correction)
3.1 Alkene hydration only needs water and heat; no catalyst is required. T / F
3.2 Bromine water (Baeyer’s reagent) can distinguish between an alkene and an alkyne. T / F
3.3 UV light is a catalyst in the free-radical halogenation of alkanes. T / F
3.4 Alkyne hydration with dilute H2SO4 and Hg2+ produces a ketone (except for ethyne, which gives ethanal). T / F
4. Function recall
Answer each question in 1–2 sentences using precise terms. 10 marks (2 each)
4.1 What is the role of Hg2+ in the hydration of an alkyne?
4.2 Why does partial hydrogenation of an alkyne require the Lindlar catalyst rather than ordinary Ni?
4.3 What distinguishes a vicinal dihalide from a geminal dihalide?
4.4 Why is complete combustion preferred over incomplete combustion in the context of petroleum refining at Ampol’s Lytton refinery (Brisbane)?
4.5 What structural feature must be present in a monomer for addition polymerisation (e.g. polyethylene production at Qenos Altona) to occur?
5. Connect the reaction types
Draw labelled arrows between the six terms below to show how they connect. Each arrow must carry a linking phrase (e.g. “converts to”, “produces”, “requires”). Aim for at least 5 labelled arrows. 5 marks
Supplied terms: alkene • alkane • alkyne • alcohol • haloalkane • polymer
Q1 — Complete conditions table
Row 1 (combustion): Reaction type: complete combustion. Conditions: high temperature (flame). Product: CO2 + H2O.
Row 2 (free-radical halogenation): Reaction type: free-radical substitution. Reagents: Cl2 or Br2. Catalyst/initiator: UV light (not a catalyst — it is the initiation energy). Product: haloalkane + HX.
Row 3 (hydrogenation of alkene): Reaction type: addition (hydrogenation). Catalyst: Ni, Pd or Pt. Product: alkane.
Row 4 (halogenation of alkene): Reaction type: addition (halogenation). Conditions: r.t., no catalyst. Product: vicinal dihalide.
Row 5 (hydrohalogenation): Reaction type: addition (hydrohalogenation). Reagents: HX (HCl, HBr, HI).
Row 6 (hydration of alkene): Reaction type: addition (hydration). Catalyst: H3PO4 or dil. H2SO4. Product: alcohol (Markovnikov).
Row 7 (full hydrogenation of alkyne): Reaction type: addition (hydrogenation). Conditions: 150–200 °C, high pressure. Product: alkane.
Row 8 (partial hydrogenation): Catalyst: Lindlar catalyst (poisoned Pd). Product: cis-alkene.
Row 9 (alkyne + HX 1 eq): Reaction type: addition (hydrohalogenation). Conditions: r.t.
Row 10 (alkyne + HX 2 eq): Reagents: HX (2 eq). Product: geminal dihalide.
Row 11 (alkyne hydration): Reaction type: addition (hydration). Catalyst: dil. H2SO4 + Hg2+. Product: ketone (or ethanal from ethyne).
Row 12 (polymerisation): Reaction type: addition polymerisation. Conditions: high temperature, high pressure, peroxide initiator. Product: polymer (e.g. polyethylene from ethene).
Q2 — Term–definition matches
2.1 D • 2.2 B • 2.3 G • 2.4 H • 2.5 C • 2.6 A • 2.7 F • 2.8 E
Q3 — True/false with correction
3.1 False. Correction: alkene hydration requires dilute H2SO4 (or H3PO4) as acid catalyst plus steam at ~300 °C and ~65 atm. Without acid catalysis the reaction is impractically slow.
3.2 False. Correction: both alkenes and alkynes decolourise bromine water (Baeyer’s reagent) by addition. The test confirms unsaturation (C=C or C≡C) but cannot distinguish between an alkene and an alkyne.
3.3 False. Correction: UV light is the initiation energy source, not a catalyst. A catalyst speeds up a reaction without being consumed; UV light is consumed (absorbed) to generate halogen radicals and initiate the chain.
3.4 True. Alkyne hydration with dil. H2SO4 + Hg2+ gives a ketone for all alkynes except ethyne (which gives ethanal because only one carbon can bear the —OH-equivalent group).
Q4 — Function recall
4.1 Hg2+ acts as a Lewis acid catalyst that activates the C≡C bond toward nucleophilic attack by water. Without it, the activation energy for alkyne hydration is too high at ~60 °C and the reaction does not proceed at a useful rate.
4.2 Ni is too active and reduces the alkyne all the way to the alkane. The Lindlar catalyst (Pd poisoned with lead acetate and quinoline) deactivates the surface just enough to stop at the alkene stage, giving cis selectivity.
4.3 In a vicinal dihalide the two halogen atoms are on adjacent (neighbouring) carbon atoms; in a geminal dihalide both halogens are on the same carbon atom.
4.4 Complete combustion releases more energy per mole of fuel and produces CO2 + H2O (less toxic products). Incomplete combustion produces CO and/or soot (carbon particulates), which are both atmospheric pollutants and represent wasted fuel value.
4.5 The monomer must contain a C=C double bond (an alkene or similar unsaturated compound). The pi bond opens during the polymerisation to allow covalent bonding between monomers, forming the polymer backbone.
Q5 — Sample concept map connections
Acceptable labelled arrows include: alkyne →partial hydrogenation (Lindlar)→ alkene; alkyne →full hydrogenation (Ni)→ alkane; alkene →hydrogenation (Ni)→ alkane; alkene →hydration (H2SO4)→ alcohol; alkene →hydrohalogenation (HX)→ haloalkane; alkyne →hydrohalogenation (HX 2eq)→ haloalkane; alkene →polymerisation (peroxide)→ polymer. Award 1 mark per correctly directed and labelled arrow (max 5).