1 This question is about covalent compounds of nitrogen.
Ammonia, NH3, is manufactured by reacting nitrogen and hydrogen gases. This is a reversible reaction and the
equilibrium is shown below.
N2(g) + 3H2(g) ⇌ 2NH3(g) ΔH = –92 kJ mol–1
i. This is an example of a dynamic equilibrium.
State 2 features of a dynamic equilibrium.
1
2
[2]
ii. State and explain the conditions of temperature and pressure that would produce a large equilibrium yield of
NH3.
[3]
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, 2 The reversible reaction below is at equilibrium.
2SO2(g) + O2(g) ⇌ 2SO3(g)
What is the expression for Kc?
A
B
C
D
Your answer [1]
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, 3 This question is about two oxides of sulfur: sulfur dioxide, SO2, and sulfur trioxide, SO3.
SO3 decomposes to form SO2 and O2, as shown in Equilibrium 18.1.
ΔH = +99 kJ mol–1 Equilibrium 18.1
i. 2.25 moles of SO3 is heated to 550 °C in the presence of a catalyst and the resulting mixture allowed to
reach equilibrium.
The equilibrium mixture contains 0.900 mol of SO2 and the total pressure is 2.80 atm.
Calculate the numerical value for Kp for Equilibrium 18.1 under these conditions and state the units of Kp.
Give your answer to 3 significant figures.
Kp = ...............................................................
units ............................................................... [5]
ii. The numerical values of Kp for Equilibrium 18.1 at temperatures T1 and T2 are shown below.
Temperature Kp
T1 3.3 × 10–5
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, T2 7.7 × 10–2
Explain why T2 is a higher temperature than T1.
[2]
iii. Suggest how the value of Kp would change if the reaction was repeated with no catalyst added and the
pressure of the system increased.
Tick (✓) one box in each row.
Change Decrease No change Increase
No catalyst
Increased pressure
[2]
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Ammonia, NH3, is manufactured by reacting nitrogen and hydrogen gases. This is a reversible reaction and the
equilibrium is shown below.
N2(g) + 3H2(g) ⇌ 2NH3(g) ΔH = –92 kJ mol–1
i. This is an example of a dynamic equilibrium.
State 2 features of a dynamic equilibrium.
1
2
[2]
ii. State and explain the conditions of temperature and pressure that would produce a large equilibrium yield of
NH3.
[3]
© OCR 2025. You may photocopy this page. 1 of 59 Created in ExamBuilder
, 2 The reversible reaction below is at equilibrium.
2SO2(g) + O2(g) ⇌ 2SO3(g)
What is the expression for Kc?
A
B
C
D
Your answer [1]
© OCR 2025. You may photocopy this page. 2 of 59 Created in ExamBuilder
, 3 This question is about two oxides of sulfur: sulfur dioxide, SO2, and sulfur trioxide, SO3.
SO3 decomposes to form SO2 and O2, as shown in Equilibrium 18.1.
ΔH = +99 kJ mol–1 Equilibrium 18.1
i. 2.25 moles of SO3 is heated to 550 °C in the presence of a catalyst and the resulting mixture allowed to
reach equilibrium.
The equilibrium mixture contains 0.900 mol of SO2 and the total pressure is 2.80 atm.
Calculate the numerical value for Kp for Equilibrium 18.1 under these conditions and state the units of Kp.
Give your answer to 3 significant figures.
Kp = ...............................................................
units ............................................................... [5]
ii. The numerical values of Kp for Equilibrium 18.1 at temperatures T1 and T2 are shown below.
Temperature Kp
T1 3.3 × 10–5
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, T2 7.7 × 10–2
Explain why T2 is a higher temperature than T1.
[2]
iii. Suggest how the value of Kp would change if the reaction was repeated with no catalyst added and the
pressure of the system increased.
Tick (✓) one box in each row.
Change Decrease No change Increase
No catalyst
Increased pressure
[2]
© OCR 2025. You may photocopy this page. 4 of 59 Created in ExamBuilder
