WACE Chemistry Practice Questions
The 64 practice questions inside the WACE Chemistry Mastery Pack, grouped by area of study. Every question comes with a full worked solution.
- Chemical equilibrium systems
- Multiple choice × 9
- Predict × 1
- Explain × 1
- Write × 1
- Acids and bases
- Multiple choice × 9
- Calculate × 1
- Explain × 1
- Determine × 1
- Oxidation and reduction
- Multiple choice × 8
- Write × 1
- Draw × 1
- Calculate × 1
- Properties and structure of organic materials
- Multiple choice × 13
- Name × 1
- Draw × 1
- Describe × 1
- Identify × 1
- Chemical synthesis
- Multiple choice × 9
- Calculate × 1
- Justify × 1
- Describe × 1
Sulfur trioxide is produced in the Contact process according to the equilibrium
2SO₂(g) + O₂(g) ⇌ 2SO₃(g) ΔH = −197 kJ mol⁻¹
The system is at equilibrium in a sealed vessel. For each of the following changes, made separately, predict the effect on the position of equilibrium (shifts left, shifts right or no change) and on the value of the equilibrium constant K (increases, decreases or no change).
- (a) The temperature is increased at constant volume.
- (b) The volume of the vessel is halved at constant temperature.
- (c) Argon gas is injected into the vessel at constant temperature and volume.
- (d) A vanadium(V) oxide catalyst is added.
Show the worked answer
Answer: Worked solution
| Change | Position of equilibrium | Value of K | Reason |
|---|---|---|---|
| (a) temperature increased | shifts left | decreases | the forward reaction is exothermic, so raising the temperature favours the endothermic reverse reaction; K is temperature dependent and falls for an exothermic reaction when the temperature rises |
| (b) volume halved | shifts right | no change | halving the volume doubles every partial pressure; the system responds by favouring the side with fewer moles of gas (2 mol on the right versus 3 mol on the left); K depends only on temperature |
| (c) argon added at constant volume | no change | no change | the total pressure rises, but the partial pressures (concentrations) of SO₂, O₂ and SO₃ are unchanged, so the forward and reverse rates are unchanged |
| (d) catalyst added | no change | no change | the catalyst lowers the activation energy of the forward and reverse reactions equally, so equilibrium is reached faster but at the same position |
One mark per row for both the position and the value of K. Exam tip: only a change in temperature changes the value of K. Changes in concentration, pressure or volume may shift the position of equilibrium, but the concentrations adjust until the same K is restored.
20 full-length practice exams with worked solutions, 20 revision notes, 64 practice questions and 200 flashcards.
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