AQA GCSE Chemistry
AQA GCSE Chemistry 4.6.2 Reversible Reactions and Dynamic Equilibrium Exam Questions
Free AQA GCSE Chemistry exam questions for 4.6.2 Reversible Reactions and Dynamic Equilibrium, with a mark scheme for every pack. Covers reversible reactions, energy changes in reversible reactions, dynamic equilibrium and the effects of concentration, temperature and pressure on equilibrium.
4.6.2 Reversible Reactions and Dynamic Equilibrium exam questions
3 question packs of real past exam questions, each with its mark scheme. Do not stop after a few: answer as many as you can without notes, then mark every answer with the mark scheme. The more questions you do, the more quickly you will spot how examiners ask about each idea.
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About AQA GCSE Chemistry 4.6.2 Reversible Reactions and Dynamic Equilibrium
AQA GCSE Chemistry 4.6.2 looks at reactions that can go both ways. You learn the symbol for reversible reactions, how energy changes reverse when the direction changes, and what happens when a reversible reaction reaches dynamic equilibrium in a closed system. At Higher tier you apply Le Chatelier's principle to predict how changes in concentration, temperature and pressure move the position of equilibrium. It is assessed on Paper 2 and links directly to the Haber process in 4.10.4. Examiners use unfamiliar reactions, so you must apply the rules rather than memorise one example.
What you need to know
- Reversible reactions Products can react to re-form the reactants. Example: ammonium chloride ⇌ ammonia + hydrogen chloride. Changing conditions, such as heating, can change the direction.
- Energy changes If a reversible reaction is exothermic in one direction it is endothermic in the opposite direction, and the same amount of energy is transferred. Example: hydrated copper sulfate (blue) ⇌ anhydrous copper sulfate (white) + water; adding water to the white solid is exothermic.
- Dynamic equilibrium In a closed system, when the forward and reverse reactions happen at exactly the same rate, equilibrium is reached. The concentrations of reactants and products stay constant but are not necessarily equal.
- Le Chatelier's principle (Higher tier only) If a system at equilibrium is subjected to a change in conditions, the position of equilibrium shifts to counteract the change.
- Concentration and temperature (Higher tier only) Increasing the concentration of a reactant shifts equilibrium to the right, forming more products. Increasing temperature shifts equilibrium in the endothermic direction; decreasing temperature favours the exothermic direction.
- Pressure (Higher tier only) For gaseous reactions, increasing pressure shifts equilibrium to the side with fewer molecules (moles of gas); decreasing pressure favours the side with more molecules.
Common mistakes in 4.6.2 Reversible Reactions and Dynamic Equilibrium
- Saying the reactions stop at equilibrium. Both reactions continue at the same rate; this is why it is 'dynamic'.
- Saying concentrations of reactants and products are equal at equilibrium. They are constant, not equal.
- Forgetting that pressure only matters when there are different numbers of gas molecules on each side.
- Saying a catalyst changes the position of equilibrium. A catalyst speeds up both reactions equally so equilibrium is reached faster, but the position does not change.
- Stating the shift without explaining it. Link the shift to opposing the change, for example 'to reduce the pressure, equilibrium moves to the side with fewer molecules'.
Try three 4.6.2 Reversible Reactions and Dynamic Equilibrium exam-style questions
1. Hydrated copper sulfate is heated and turns white. Water is then added. Describe and explain what happens. (3 marks)
Show the mark scheme answer
The white anhydrous copper sulfate turns blue; the reaction is reversible; the reverse reaction is exothermic so the mixture gets hot (same energy as taken in when heated).
2. N2(g) + 3H2(g) ⇌ 2NH3(g). Explain the effect of increasing pressure on the yield of ammonia. (3 marks) Higher tier only
Show the mark scheme answer
Yield increases; there are 4 molecules of gas on the left and 2 on the right; equilibrium shifts to the side with fewer molecules to reduce the pressure.
3. State two features of a reaction at dynamic equilibrium. (2 marks)
Show the mark scheme answer
The forward and reverse reactions happen at the same rate; concentrations of reactants and products remain constant (in a closed system).
4.6.2 Reversible Reactions and Dynamic Equilibrium FAQs
What does AQA GCSE Chemistry 4.6.2 cover?
It covers reversible reactions, energy changes in reversible reactions, dynamic equilibrium in closed systems and, at Higher tier, how concentration, temperature and pressure affect the position of equilibrium.
Which paper is equilibrium on?
Section 4.6 is assessed on AQA GCSE Chemistry Paper 2.
Which parts of 4.6.2 are Higher tier only?
Le Chatelier's principle and the effects of changing concentration, temperature and pressure on equilibrium are Higher tier only. Reversible reactions, energy changes and the idea of equilibrium are on both tiers.
