Quick answer: A reversible reaction can go in both directions, and in a closed system it reaches dynamic equilibrium when the forward and reverse rates are equal and concentrations stay constant. This Chemistry 9-10 test on chemical equilibrium has 8 questions worth 20 marks, to do in 45 minutes: key terms, concentration graph and phosphorus pentachloride. The mark scheme is on a separate page; free printable PDF.
This test lasts 45 minutes and is worth 20 marks. Answer every question. Also, for explanations, link the change to the direction of shift and say why using Le Chatelier’s principle. Finally, show each step in calculations.
Level: Chemistry grades 9-10 (GCSE · IGCSE · O Level · Class 9-10) · Curriculum: HS-PS1-6
Question 1 Key terms (3 marks)
- Firstly, state what is meant by a reversible reaction. (1 mark)
- Then explain what is meant by dynamic equilibrium. (2 marks)
Question 2 Concentration graph (4 marks)
Reaction A ⇌ B takes place in a closed container, so the graph shows the concentrations.- Firstly, state the time when equilibrium is reached. (1 mark)
- Then state the concentration of A and of B at equilibrium. (1 mark)
- Finally, explain why the concentrations stop changing although the reactions have not stopped. (2 marks)
Question 3 Phosphorus pentachloride (3 marks)
PCl₅(g) ⇌ PCl₃(g) + Cl₂(g), ΔH = +93 kJ/mol.- Firstly, predict the shift when you increase the pressure and explain why. (2 marks)
- Then predict the shift when you raise the temperature. (1 mark)
Question 4 Conditions in the Haber process (3 marks)
The Haber process uses about 450 °C, 200 atm and an iron catalyst for N₂ + 3H₂ ⇌ 2NH₃ (ΔH negative). Then explain why the process uses 450 °C instead of a lower temperature. (3 marks)Question 5 Catalyst (2 marks)
You add a catalyst to a system at equilibrium. Then state and explain its effect on the position of equilibrium and on the time to reach it. (2 marks)Question 6 Ammonia calculation (2 marks)
Firstly, a reactor holds 60 mol of N₂ and 180 mol of H₂. Then at equilibrium 20% of the nitrogen has reacted. Calculate the moles of ammonia and of nitrogen left. (2 marks)Question 7 Recycling (2 marks)
Explain why the Haber process returns unreacted nitrogen and hydrogen to the reactor. (2 marks)Question 8 Use of ammonia (1 mark)
Finally, state one important use of ammonia. (1 mark)
