1 Hydrogen gas is manufactured by the chemical industry from the reversible reaction of methane and steam,
shown below.
CH4(g) + H2O(g) ⇌ 3H2(g) + CO(g) ΔH = +195 kJ mol–1
Average bond enthalpies are shown in the table.
Bond H–H O–H C=O
Average bond enthalpy / kJ mol–1 +436 +464 +1077
i. Why do all average bond enthalpies have a positive value?
[1]
ii. Determine the C–H bond enthalpy, in kJ mol–1, using the information above.
C–H bond enthalpy = ................................................... kJ mol–1[3]
iii. Hydrogen gas is being considered as a household fuel to replace methane.
The enthalpy change of formation, ΔfH, for H2O(l) is –285.8 kJ mol–1.
Determine the energy released when 60.0 m3 of hydrogen is used as a household fuel at RTP.
Give your answer to 3 significant figures and in standard form.
energy released = ................................................... kJ [2]
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, 2 This question is about covalent compounds of nitrogen.
Hydrazine, N2H4, shown below, can be used as a rocket fuel.
As a fuel, N2H4 reacts with oxygen as shown below.
N2H4(g) + O2(g) → N2 (g) + 2H2O(g) ΔH = –581 kJ mol–1
Average bond enthalpies are shown in the table.
Bond N–N O=O N≡N O–H
Average bond enthalpy / kJ mol–1 +158 +498 +945 +464
Calculate the average bond enthalpy of the N–H bond.
average bond enthalpy of N–H = ............................................ kJ mol–1 [3]
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, 3 An enthalpy cycle is shown below.
What is ΔrH, in kJ mol-1, shown in the enthalpy cycle?
A +676
B +110
C -110
D -676
Your answer [1]
4 A mixture of gases is heated in a closed container. The reaction rate increases.
Which statement explains why the rate increases?
A More molecules have an energy greater than the activation energy.
B The activation energy decreases.
C The activation energy increases.
D The concentration of the gases increases.
Your answer [1]
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, 5 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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shown below.
CH4(g) + H2O(g) ⇌ 3H2(g) + CO(g) ΔH = +195 kJ mol–1
Average bond enthalpies are shown in the table.
Bond H–H O–H C=O
Average bond enthalpy / kJ mol–1 +436 +464 +1077
i. Why do all average bond enthalpies have a positive value?
[1]
ii. Determine the C–H bond enthalpy, in kJ mol–1, using the information above.
C–H bond enthalpy = ................................................... kJ mol–1[3]
iii. Hydrogen gas is being considered as a household fuel to replace methane.
The enthalpy change of formation, ΔfH, for H2O(l) is –285.8 kJ mol–1.
Determine the energy released when 60.0 m3 of hydrogen is used as a household fuel at RTP.
Give your answer to 3 significant figures and in standard form.
energy released = ................................................... kJ [2]
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, 2 This question is about covalent compounds of nitrogen.
Hydrazine, N2H4, shown below, can be used as a rocket fuel.
As a fuel, N2H4 reacts with oxygen as shown below.
N2H4(g) + O2(g) → N2 (g) + 2H2O(g) ΔH = –581 kJ mol–1
Average bond enthalpies are shown in the table.
Bond N–N O=O N≡N O–H
Average bond enthalpy / kJ mol–1 +158 +498 +945 +464
Calculate the average bond enthalpy of the N–H bond.
average bond enthalpy of N–H = ............................................ kJ mol–1 [3]
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, 3 An enthalpy cycle is shown below.
What is ΔrH, in kJ mol-1, shown in the enthalpy cycle?
A +676
B +110
C -110
D -676
Your answer [1]
4 A mixture of gases is heated in a closed container. The reaction rate increases.
Which statement explains why the rate increases?
A More molecules have an energy greater than the activation energy.
B The activation energy decreases.
C The activation energy increases.
D The concentration of the gases increases.
Your answer [1]
© OCR 2025. You may photocopy this page. 3 of 108 Created in ExamBuilder
, 5 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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