CHEM20018 · Chemistry: Reactions And Synthesis
The Complete Exam Bible · S1 2026Chemistry: Reactions and Synthesis
CHEM20018 Chemistry: Reactions and Synthesis is the University of Melbourne's second-year subject where first-year chemistry grows teeth — five mini-courses taught by five lecturers and examined as five separate sections (A–E) in one paper. The whole grade rests on a 3-hour closed-book on-campus exam worth 80% (Section A organic synthesis alone is 60 marks, roughly half the paper), with the remaining 20% from five short online LMS tests across the semester. You stop memorising single reactions and start designing multi-step syntheses, predicting whether an ionic solid is stable from a thermodynamic cycle, and reading a redox diagram to decide whether a species disproportionates.
What CHEM20018 covers
The whole subject → one exam-ready map. Each topic links to its free chapter guide.
How CHEM20018 is assessed
| Component | Weight | Format |
|---|---|---|
| 5 online LMS tests (released end of Weeks 2, 4, 6, 8, 10; each covers the previous 2 weeks; 30 min once commenced, no save-and-return; open 1 week; equally weighted) | 20% total (4% each) | Online short tests via LMS |
| Written examination (3-hour closed-book on-campus; 15 min reading + 3 h writing; 5 sections A–E, all short answer, attempt ALL questions; Casio FX-82 + unassembled molecular models permitted; appendices booklet provided) | 80% | On-campus written exam |
Closed-book signature: Born–Mayer lattice enthalpy + thermal-stability reasoning (Section B)
- 2 marks — correct trend + the 1/d justification(a) Lattice enthalpy scales as ΔHL ∝ |z₊z₋| ÷ d. Charges are identical (+2/−2) across the group, so the only variable is the interionic distance d. Cation radius increases Mg2+ → Ca2+ → Sr2+ → Ba2+, so d rises and |ΔHL| falls steadily down the group.
- 2 marks — d and the charge product(b) Compute the interionic distance: d = r(Sr2+) + r(O2−) = 118 + 140 = 258 pm. Take zAzB = |(+2)(−2)| = 4.
- 2 marks — correct substitution and arithmeticSubstitute: ΔHL = (1.389×10⁵ × 1.7476 × 4 ÷ 258)(1 − 34.5÷258) = (9.71×10⁵ ÷ 258)(1 − 0.1337) = 3763 × 0.8663 ≈ 3.26×10³ kJ mol⁻¹ in magnitude (i.e. ΔHL ≈ −3.3×10³ kJ mol⁻¹, sign negative for lattice formation).
- 2 marks — correct lattice-mismatch reasoning, not just 'Ba is bigger'(c) Thermal-stability (lattice-mismatch) argument: decomposition is MSO₄(s) → MO(s) + SO₃(g). A large cation (Ba2+) is a poor size-match for the small oxide product but a good match for the large sulfate anion, so the sulfate is stabilised relative to the oxide; the small cation case (Sr2+) gains more lattice enthalpy on forming the small oxide, giving a larger driving force to decompose. Hence BaSO₄ needs a higher temperature to decompose than SrSO₄.
Key terms
- Enolate
- The resonance-stabilised conjugate base formed by removing an α-hydrogen next to a C=O; negative charge is delocalised over the α-carbon and oxygen, making the α-carbon a carbon nucleophile.
- Aldol condensation
- Base- or acid-promoted reaction of an enolate with a carbonyl that, on heating, loses water (E1cb) to give an α,β-unsaturated carbonyl; the un-dehydrated product is the β-hydroxy carbonyl 'aldol'.
- Born–Haber cycle
- A Hess's-law thermodynamic cycle relating the formation enthalpy of an ionic solid to atomisation, ionisation energy, electron affinity and lattice enthalpy; used to solve for any one unknown leg.
- Disproportionation
- A single species is simultaneously oxidised and reduced; favoured when the potential of the couple to its right exceeds that to its left (a convex 'bump' above its neighbours on a Frost diagram).
- Chelate effect
- The extra thermodynamic stability of complexes of multidentate ligands over comparable monodentate ones, driven mainly by a favourable entropy change as more free particles are released into solution.
- Carnot cycle
- An idealised reversible heat-engine cycle of two isothermal and two adiabatic steps; its efficiency η = 1 − TC/TH sets the maximum work obtainable between two reservoirs, and over a full cycle ΔU = 0 and ΔS = 0.
CHEM20018 FAQ
Is CHEM20018 really five separate subjects in one exam?
Effectively yes. Five lecturers each own a block — organic synthesis (Wong), inorganic thermodynamics (Abrahams), coordination chemistry (Donnelly), physical-chemistry thermodynamics (Smith) and materials (Hutchison) — and the exam is divided into Sections A–E that mirror them. You must attempt ALL questions, so there is nowhere to hide a weak section.
How is the mark split, and which section matters most?
The exam is 80% and the five online LMS tests are 20% (4% each). Inside the exam, Section A (organic synthesis) is 60 marks — about half the paper — while Sections B, C, D and E are 30 marks each. Organic synthesis is therefore the single biggest lever on your grade.
Is it open-book? What can I bring in?
It is closed-book. You may bring a Casio FX-82 calculator (any suffix) and an unassembled molecular model kit in a clear zip-lock bag, plus pens, rulers and mathematical instruments. An appendices booklet (periodic table, physical constants, thermodynamic relations, Madelung constants, the D-aldose family tree) is provided in the exam and collected at the end — so the value of a study guide is concept mastery and worked-method drills, not a smuggled formula sheet.
Do I have to memorise the Born–Mayer, Kapustinskii and Carnot formulae?
No — the key thermodynamic relations and constants sit in the provided appendix. Examiners are testing whether you can select the right relation and execute it cleanly: convert radii to a distance in pm, get the charge product, substitute, and check the sign. Drill the method, not the constants.
What background do I need before CHEM20018?
It builds directly on first-year chemistry (CHEM10003/CHEM10004). You should be comfortable with curly-arrow mechanisms, basic carbonyl chemistry, simple thermodynamics (ΔH, ΔG, equilibrium) and reading a periodic table. The subject's job is to turn that vocabulary into the ability to design syntheses and reason from thermodynamic cycles and redox diagrams.
How to study for the exam
Treat CHEM20018 as five exams stitched together and budget your revision by marks, not by interest. Front-load Section A (organic, 60 marks ≈ half the paper): build a personal 'reaction matrix' of every named reaction (HVZ → aldol/Claisen/Dieckmann → malonate/acetoacetate → Michael/Mannich → carbohydrate redox/Kiliani–Fischer), and for each one drill forward (reagents → product) and backward (retrosynthesis: which disconnection regenerates these synthons). Practise drawing mechanisms with curly arrows until they are automatic.
For the four 30-mark sections, the exam rewards method discipline over memorisation because the appendix supplies constants and relations. For B and D, rehearse the calculation pipelines (Born–Haber/Born–Mayer/Kapustinskii; reversible-isothermal w, q, ΔS; Carnot efficiency) and always carry units and signs. For B and the redox diagrams, learn to read Ellingham, Latimer, Frost and Pourbaix plots fast — slope = E°, convex bump = disproportionation. For C, master the qualitative arguments (Irving–Williams, chelate effect, HSAB, labile vs inert, associative Pt(II)) since they recur as short-answer. For E, the Coulomb, Lennard-Jones and band-gap (λ ≈ 1240/Eg) relations are quick marks if you can plug-and-chug.
Use the five LMS tests as a free progress diagnostic: each covers the previous two weeks, so a poor test result flags exactly which block to repair before the section goes cold. Finish with full mock-exam timing — 30 minutes per 30-mark section — because running out of time on Section A is the most common way strong students lose marks.
