Pearson Edexcel International GCSE in Chemistry · 4CH1 · Free · no account needed
Dynamic Equilibrium — exam questions
12 original Incandio exam-style questions on Dynamic Equilibrium, 26 marks, about 26 minutes of writing. Each one carries the command word, the tariff and the specification statement it assesses, exactly as a paper presents them. This is an original Incandio practice question, written to reflect the structure and demands of the qualification. It is not an official Pearson Edexcel past-paper question.
This is the practice set for Dynamic Equilibrium — the lesson that teaches it. Read the lesson first if the idea is new; come here when you want to find out whether you can turn it into marks. Completely free, no account needed to read.
What these questions ask of you
6 command words run through this set, and on Pearson Edexcel International GCSE Chemistry each one means something precise. Answering the wrong command is the commonest way a candidate who understands the lesson still loses the mark.
- Which (1 mark)
- one option chosen from the set given
- Give (1–2 marks)
- a short factual answer — the most common chemistry command
- State (1 mark)
- one precise fact, no justification
- Describe (2–5 marks)
- developed, linked statements of what happens or what is observed Misread as: giving one bare observation where the tariff asked for a developed account
- Explain (2–4 marks)
- the reason, in terms of particles, bonding, energy or equilibrium Misread as: describing the observation without giving the chemistry that causes it
- Suggest (1–3 marks)
- a plausible answer applying taught chemistry to an unfamiliar substance
Assessed on Paper 1 (4CH1/1C) and Paper 2 (4CH1/2C), against AO1, AO2, AO3.
Where these sit in the specification
Pearson Edexcel International GCSE Chemistry (4CH1) — statements 3.20 · 3.19 · 3.21 · 3.22. Incandio is aligned to this specification; it is not published by, endorsed by or affiliated with Pearson, and it reproduces none of Pearson's wording.
The 12 questions
Answer them on paper, then open the lesson's exam practice to have them marked. The mark scheme, the accepted and rejected answers and the annotated model answer are in Incandio and are not printed here — an answer beside its question is not practice.
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Nitrogen and hydrogen react in a sealed vessel to form ammonia: N₂ + 3H₂ ⇌ 2NH₃. The forward reaction is exothermic. The mixture is left until the concentrations of all three gases stop changing.
Table 1 — percentage of ammonia in the equilibrium mixture Pressure / atm at 200 °C at 350 °C at 500 °C 50 74 35 9 200 89 62 26 400 95 79 44 (a)
(1)Give
Give the percentage of ammonia obtained at 200 atm and 350 °C, using Table 1.
Nitrogen and hydrogen react in a sealed vessel to form ammonia: N₂ + 3H₂ ⇌ 2NH₃. The forward reaction is exothermic. The mixture is left until the concentrations of all three gases stop changing.
Table 1 — percentage of ammonia in the equilibrium mixture Pressure / atm at 200 °C at 350 °C at 500 °C 50 74 35 9 200 89 62 26 400 95 79 44 percentage of ammonia obtained = ............................ %
(b)
(2)Describe
Describe the two trends shown in Table 1.
Nitrogen and hydrogen react in a sealed vessel to form ammonia: N₂ + 3H₂ ⇌ 2NH₃. The forward reaction is exothermic. The mixture is left until the concentrations of all three gases stop changing.
Table 1 — percentage of ammonia in the equilibrium mixture Pressure / atm at 200 °C at 350 °C at 500 °C 50 74 35 9 200 89 62 26 400 95 79 44 (c)
(3)Explain
Explain the pressure trend in Table 1, using the equation in the stimulus.
Nitrogen and hydrogen react in a sealed vessel to form ammonia: N₂ + 3H₂ ⇌ 2NH₃. The forward reaction is exothermic. The mixture is left until the concentrations of all three gases stop changing.
Table 1 — percentage of ammonia in the equilibrium mixture Pressure / atm at 200 °C at 350 °C at 500 °C 50 74 35 9 200 89 62 26 400 95 79 44 (d)
(3)Suggest
Ammonia is made industrially at about 450 °C, not at 200 °C where Table 1 shows a far higher yield. Suggest why.
Nitrogen and hydrogen react in a sealed vessel to form ammonia: N₂ + 3H₂ ⇌ 2NH₃. The forward reaction is exothermic. The mixture is left until the concentrations of all three gases stop changing.
Table 1 — percentage of ammonia in the equilibrium mixture Pressure / atm at 200 °C at 350 °C at 500 °C 50 74 35 9 200 89 62 26 400 95 79 44 (Total for Question 1 = 9 marks)
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(1)Which
Which is true of a reaction at dynamic equilibrium?
Statement A both reactions have stopped B the forward and reverse rates are equal C the amounts of reactants and products are equal D only the forward reaction is happening (Total for Question 2 = 1 mark)
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(1)Give
Give the condition a reaction vessel must meet for equilibrium to be reached.
(Total for Question 3 = 1 mark)
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(1)State
State the effect of a catalyst on the position of an equilibrium.
(Total for Question 4 = 1 mark)
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(2)Describe
Describe two characteristics of a reaction that has reached dynamic equilibrium.
(Total for Question 5 = 2 marks)
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(3)Explain
Explain why the concentrations stop changing at equilibrium although neither reaction has stopped.
(Total for Question 6 = 3 marks)
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(2)Explain
Explain why adding a catalyst does not change the position of an equilibrium.
(Total for Question 7 = 2 marks)
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(3)Explain
Explain the effect of raising the temperature on the position of an equilibrium whose forward reaction is exothermic.
(Total for Question 8 = 3 marks)
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(4)Explain
In one industrial process the product is drawn off continuously as it forms, instead of being left in the vessel. Explain the effect of this on the position of the equilibrium and on the amount of product obtained.
(Total for Question 9 = 4 marks)
Have them marked, then defend the answer
Practice tells you the mark; teaching it back tells you whether you understand it. On Incandio a topic counts as mastered only once you have taught it and defended it.
- Mark these questions — 12 questions, marked on Incandio against the authored scheme, with the mistake you actually made named.
- Teach it — explain Dynamic Equilibrium to Ember, an AI pupil who does not have it yet and asks the awkward question.
- Defend it — argue it against Marcellin Berthelot over three rounds, marked against descriptors you can read first.
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Back to the lesson
- Dynamic Equilibrium — Nothing appears to be happening, everything is still happening — and that is what lets conditions shift it.
- All of Incandio Chemistry · Incandio Exam Practice