Edexcel A Level Chemistry
Edexcel A Level Chemistry Topic 10: Equilibrium I Exam Questions
Free Edexcel A Level Chemistry exam questions for Topic 10: Equilibrium I, with a mark scheme for every pack. Covers reversible reactions, dynamic equilibrium, Le Chatelier’s principle, effects of concentration, pressure, temperature and catalysts, and writing Kc expressions.
Topic 10: Equilibrium I exam questions
1 question pack 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 Edexcel A Level Chemistry Topic 10: Equilibrium I
Topic 10 of Edexcel A Level Chemistry, Equilibrium I, introduces reversible reactions and dynamic equilibrium in closed systems. You use Le Chatelier's principle to predict how changes in concentration, pressure and temperature affect the position of equilibrium, and explain why a catalyst does not affect the position but helps equilibrium be reached faster. The topic covers compromise conditions in industrial processes, balancing rate, yield, cost and safety, and introduces the equilibrium constant expression Kc for homogeneous systems. It is assessed in Paper 1 and leads directly into Topic 11 (Equilibrium II), where Kc and Kp are calculated and the effect of temperature on K is explained.
What you need to know
- Dynamic equilibrium In a closed system the rates of the forward and backward reactions are equal and the concentrations of reactants and products remain constant.
- Le Chatelier's principle If a system at equilibrium is disturbed, the position of equilibrium shifts to oppose the change. Increasing concentration of a reactant shifts it to the right.
- Pressure Increasing pressure shifts equilibrium towards the side with fewer gas molecules. Pressure has no effect when both sides have the same number of gas moles.
- Temperature Increasing temperature shifts the equilibrium in the endothermic direction. This is the only change that alters the value of the equilibrium constant.
- Catalysts A catalyst increases the rates of the forward and backward reactions equally, so equilibrium is reached faster but its position is unchanged.
- Kc expressions For aA + bB ⇌ cC + dD, Kc = [C]^c[D]^d/([A]^a[B]^b) using equilibrium concentrations. Write expressions for homogeneous equilibria.
- Industrial compromise Processes such as ammonia and methanol production use moderate temperatures and pressures with a catalyst to balance yield, rate, energy costs and safety.
Common mistakes in Topic 10: Equilibrium I
- Saying the forward and backward reactions stop at equilibrium; both continue at equal rates.
- Saying concentrations of reactants and products are equal at equilibrium; they are constant, not necessarily equal.
- Claiming a catalyst increases yield; it only speeds up the time taken to reach equilibrium.
- Applying the pressure argument using the total number of molecules including solids and liquids; count only gaseous moles.
- Writing a Kc expression upside down with reactants on top.
Try three Topic 10: Equilibrium I exam-style questions
1. For 2SO2(g) + O2(g) ⇌ 2SO3(g), delta H = -197 kJ mol-1, state and explain the effect of raising the temperature on the yield of SO3. (2 marks)
Show the mark scheme answer
Yield decreases; forward reaction is exothermic so equilibrium shifts in the endothermic (backward) direction to absorb the added heat.
2. Write the Kc expression for N2(g) + 3H2(g) ⇌ 2NH3(g). (1 mark)
Show the mark scheme answer
Kc = [NH3]^2/([N2][H2]^3).
3. Explain why a moderate temperature is used in the Haber process rather than a low temperature. (2 marks)
Show the mark scheme answer
Low temperature would give a higher yield because the reaction is exothermic; but the rate would be too slow, so a compromise temperature gives an acceptable yield at an acceptable rate.
Topic 10: Equilibrium I FAQs
What does Edexcel A Level Chemistry Topic 10 Equilibrium I cover?
It covers reversible reactions, dynamic equilibrium, Le Chatelier's principle, effects of conditions and catalysts, and writing Kc expressions.
Which paper is Equilibrium I examined in?
Topic 10 is assessed in Paper 1, and equilibrium ideas also appear in Paper 3.
How do I answer Le Chatelier questions for full marks?
State the direction of the shift, then give the reason linked to the change, such as fewer gas moles or the endothermic direction.
