VCE Chemistry 2025

Walkthrough of the 2025 VCE chemistry exam: what it assessed, strategy tips, and the common errors flagged in the official marker report.

Marks: 120
Time: 150 min
Authority: VCAA
Updated: 2026-05-29

Open the official PDF ->Official marking notes

What this paper assessed

The VCE Chemistry Units 3 and 4 examination (120 marks, 150 minutes) assesses the VCAA study design across:

Unit 3 - How can chemical processes be designed to optimise efficiency: chemical energy (fuels, calorimetry, thermochemical equations), redox reactions, galvanic and electrolytic cells and the electrochemical series, rates of reaction and the collision theory, and equilibrium including $K_{c}$ and Le Chatelier's principle.
Unit 4 - How are organic compounds categorised, analysed and used: the structure, naming and reactions of organic families (alkanes, haloalkanes, alcohols, carboxylic acids, esters), reaction pathways, analytical techniques (mass spectrometry, IR, ¹H and ¹³C NMR, chromatography), and the chemistry of food (proteins, carbohydrates, fats, vitamins).

You are given the VCAA data book and periodic table. The exam combines multiple choice (Section A) with short and extended answer (Section B). It rewards balanced thermochemical and ionic equations with states, calculations that show the relationship before the arithmetic, and answers to correct significant figures.

Structure and timing

The paper is 120 marks in 150 minutes (plus 15 minutes reading time) - about 1.25 minutes per mark.

Section A - Multiple choice (~30 marks): budget about 35 minutes.
Section B - Short and extended answer (~90 marks): budget about 115 minutes, with multi-step calculations and structure-determination items getting a brief plan.

Use the 15 minutes reading time to flag the heaviest calculation (often calorimetry or electrolysis with charge) and the spectroscopy structure-determination question. Keep the last ~10 minutes to check states, units and significant figures.

Worked practice questions (exam-style)

Worked example

Question 1 (5 marks): In an electrolysis experiment, a current of $2.0\ \text{A}$ is passed through molten copper(II) chloride for $30$ minutes. Calculate the mass of copper deposited at the cathode. ( $F = 96\,500\ \text{C mol}^{-1}$ , $M(\text{Cu}) = 63.5\ \text{g mol}^{-1}$ .)

The cathode half-equation is $\text{Cu}^{2+} + 2e^- \rightarrow \text{Cu}$ , so $2$ mol of electrons deposit $1$ mol of copper.

Charge passed: $Q = It = 2.0 \times (30 \times 60) = 2.0 \times 1800 = 3600\ \text{C}$ .

Moles of electrons: $n(e^-) = \dfrac{Q}{F} = \dfrac{3600}{96\,500} = 0.0373\ \text{mol}$ .

Moles of copper: $n(\text{Cu}) = \dfrac{0.0373}{2} = 0.01865\ \text{mol}$ (since 2 electrons per Cu).

Mass: $m = n \times M = 0.01865 \times 63.5 = 1.18\ \text{g}$ .

So about $1.2\ \text{g}$ of copper is deposited. The common slip is forgetting the factor of 2 from the two-electron reduction.

Worked example

Question 2 (4 marks): For the equilibrium $\text{N}_2\text{O}_4(g) \rightleftharpoons 2\text{NO}_2(g)$ , $\Delta H = +57\ \text{kJ mol}^{-1}$ . Explain, using Le Chatelier's principle, the effect on the amount of NO₂ of (a) increasing temperature and (b) decreasing the volume of the container.

(a) Increasing temperature: the forward reaction is endothermic ( $\Delta H>0$ ), so heat behaves as a reactant. Adding heat shifts the equilibrium right (the endothermic direction) to absorb it, increasing the amount of NO₂ and increasing $K_c$ .

(b) Decreasing the volume raises the pressure, so the system shifts to the side with fewer moles of gas to partially oppose the change. The left has 1 mol; the right has 2 mol. The equilibrium shifts left, decreasing the amount of NO₂ (though $K_c$ is unchanged, since only temperature affects $K_c$ ).

Each mark requires the driver: endothermic direction for temperature, moles of gas for volume - and noting that $K_c$ changes only with temperature.

Worked example

Question 3 (6 marks): A compound with molecular formula $\text{C}_3\text{H}_6\text{O}_2$ gives an IR absorption near $1700\ \text{cm}^{-1}$ and a broad absorption around $2500$ - $3300\ \text{cm}^{-1}$ , and its ¹H NMR shows three peaks. Deduce the structure and justify using the data.

The molecular formula $\text{C}_3\text{H}_6\text{O}_2$ has one degree of unsaturation (consistent with a C=O group).

The IR absorption near $1700\ \text{cm}^{-1}$ indicates a carbonyl (C=O), and the broad absorption over $2500$ - $3300\ \text{cm}^{-1}$ is characteristic of the O-H of a carboxylic acid (broadened by hydrogen bonding). Together these point to a carboxylic acid functional group, $-\text{COOH}$ .

With three carbons, the structure is propanoic acid, $\text{CH}_3\text{CH}_2\text{COOH}$ . The ¹H NMR showing three peaks matches its three proton environments: the $-\text{CH}_3$ (triplet), the $-\text{CH}_2-$ (quartet), and the acidic $-\text{COOH}$ proton (a distinct, often downfield, singlet). The justification must tie each spectroscopic feature to the structural conclusion, not just name the compound.

Common errors students made

The VCAA assessor's report patterns flagged students omitting state symbols, mixing up oxidising and reducing agents, and quoting Le Chatelier shifts without naming the driver; energy diagrams were often unlabelled or drawn without an activation-energy marker. Further recurring traps:

Dropping the electron-ratio factor in Faraday/electrolysis calculations (e.g. forgetting Cu²⁺ needs 2 electrons).
Confusing the oxidant and reductant, or misidentifying which species is oxidised (loses electrons) versus reduced.
Significant-figure and unit errors, including rounding mid-calculation.
Assigning a single spectroscopic peak to a structure without using the molecular formula and degrees of unsaturation to corroborate.
Stating that $K_c$ changes with pressure or concentration - it changes only with temperature.

How to use this paper

Sit Section A in 35 minutes and Section B in 115 minutes under exam conditions. Mark strictly against the official VCAA assessment report and answers at the links in the frontmatter. Rebuild every calculation that lost more than half its marks, writing the governing relationship on its own line before substituting and re-checking sig figs. For structure-determination items, practise combining molecular formula, IR and NMR before naming a compound. Keep an error log of recurring slips (states, oxidant/reductant, electron ratios, $K_c$ conditions) and re-test the exact class next session.

Use this paper well

Sit the paper under exam conditions (150 minutes, 120 marks).
Mark yourself against the official VCAA marking notes.
Compare against the Chemistry hub to find the syllabus dot points this paper tested.

What this paper assessed

Structure and timing

Worked practice questions (exam-style)

Common errors students made

How to use this paper

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