EnergeticsEdexcel International A Level Chemistry: Topic test

20 questions, 54 marks

Edexcel International A Level Chemistry

Energetics topic test

Total 54 marks

Name

Class

Date

1
Sulfur burns in oxygen to form sulfur dioxide: S(s) + O₂(g) → SO₂(g), ΔH = −297 kJ mol⁻¹ at 298 K and 100 kPa. Relative atomic mass: S = 32.1.
(a)
Which standard enthalpy change or changes does the value −297 kJ mol⁻¹ represent?
[1 mark]
AThe standard enthalpy change of combustion of sulfur only
BThe standard enthalpy change of formation of sulfur dioxide only
CThe standard enthalpy change of combustion of sulfur and of formation of sulfur dioxide
DThe standard enthalpy change of atomisation of sulfur
(b)
Which statement correctly describes an enthalpy level diagram for this reaction?
[1 mark]
AThe products lie below the reactants and the arrow for ΔH points downwards
BThe products lie above the reactants and the arrow for ΔH points upwards
CThe products lie below the reactants and the arrow for ΔH points upwards
DThe products and reactants lie at the same level
(c)
Calculate the energy released, in kJ, when 4.00 g of sulfur burns completely in oxygen.
[2 marks]
Total for question 1: 4 marks
2
A student dissolves 5.00 g of ammonium nitrate, NH₄NO₃ (Mr = 80.0), in 100.0 g of water in a polystyrene cup. The temperature falls from 21.5 °C to 16.3 °C. Assume that the specific heat capacity of the solution is 4.18 J g⁻¹ °C⁻¹ and that the mass heated is 100.0 g.
(a)
What is the enthalpy change of solution of ammonium nitrate, in kJ mol⁻¹?
[1 mark]
A−34.8
B+34.8
C+2.17
D+1.74
(b)
Which statement explains why the experimental value is likely to be smaller in magnitude than the true value?
[1 mark]
AHeat is lost from the solution to the surroundings, so the temperature fall is too large
BThe polystyrene cup is a good conductor of heat
CThe mass in q = mcΔT should be the 5.00 g of solid only
DHeat is gained from the surroundings, so the temperature fall is smaller than it should be
(c)
Each temperature reading has an uncertainty of ±0.1 °C. Calculate the percentage uncertainty in the temperature change.
[2 marks]
Total for question 2: 4 marks
3
Ethyne, C₂H₂, is used in welding. Its standard enthalpy change of formation cannot be measured directly. Standard enthalpy changes of combustion / kJ mol⁻¹: carbon (graphite) −393.5; hydrogen −285.8; ethyne −1299.6.
(a)
Use these data to calculate the standard enthalpy change of formation of ethyne, 2C(s) + H₂(g) → C₂H₂(g).
[3 marks]
(b)
The standard enthalpy change of formation of ethane is −84.0 kJ mol⁻¹. Calculate the enthalpy change for C₂H₂(g) + 2H₂(g) → C₂H₆(g), state why the standard enthalpy change of formation of hydrogen gas is zero, and state Hess's law.
[4 marks]
Total for question 3: 7 marks
4
A student determines the enthalpy change of combustion of butan-1-ol, C₄H₉OH (Mr = 74.0), with a spirit burner. She burns 0.740 g of the alcohol and heats 150.0 g of water in a metal can, raising its temperature from 20.2 °C to 38.0 °C. The specific heat capacity of water is 4.18 J g⁻¹ °C⁻¹. The data book value is −2676 kJ mol⁻¹.
(a)
Calculate the experimental enthalpy change of combustion of butan-1-ol. Give two reasons why it differs from the data book value and suggest one improvement to the experiment.
[6 marks]
(b)
The standard enthalpy changes of formation of carbon dioxide and liquid water are −393.5 kJ mol⁻¹ and −285.8 kJ mol⁻¹. Use these and the data book value to calculate the standard enthalpy change of formation of butan-1-ol, showing the equations involved.
[6 marks]
Total for question 4: 12 marks
5
Hydrazine, N₂H₄, can decompose into its elements in the gas phase: N₂H₄(g) → N₂(g) + 2H₂(g). Mean bond enthalpies / kJ mol⁻¹: N–H 391; N–N 158; N≡N 945; H–H 436.
(a)
What is the enthalpy change for this decomposition, in kJ mol⁻¹, calculated from mean bond enthalpies?
[1 mark]
A−95
B+95
C−1817
D+1722
(b)
Which statement explains why the value calculated from mean bond enthalpies may differ from the true enthalpy change?
[1 mark]
ABond making and bond breaking both absorb energy
BMean bond enthalpies apply only at 0 K
CMean bond enthalpies are averages over many compounds, so they differ from the actual bond enthalpies in hydrazine
DThe calculation ignores the N≡N bond
(c)
Use the bond enthalpy data to deduce which bond in hydrazine is most likely to break first, and explain how this affects how readily hydrazine reacts.
[2 marks]
Total for question 5: 4 marks
6
In the thermite reaction, powdered aluminium reduces iron(III) oxide: 2Al(s) + Fe₂O₃(s) → Al₂O₃(s) + 2Fe(s), ΔrH = −852 kJ mol⁻¹. Relative atomic mass: Al = 27.0.
(a)
How much heat energy is released when 5.40 g of aluminium reacts completely?
[1 mark]
A42.6 kJ
B170 kJ
C852 kJ
D85.2 kJ
(b)
Which equation represents the standard enthalpy change of formation of aluminium oxide?
[1 mark]
A4Al(s) + 3O₂(g) → 2Al₂O₃(s)
B2Al(s) + 1½O₂(g) → Al₂O₃(s)
CAl₂O₃(s) → 2Al(s) + 1½O₂(g)
D2Al(s) + Fe₂O₃(s) → Al₂O₃(s) + 2Fe(s)
(c)
The standard enthalpy change of formation of iron(III) oxide is −824 kJ mol⁻¹. Calculate the standard enthalpy change of formation of aluminium oxide.
[2 marks]
Total for question 6: 4 marks
7
A student adds 0.150 g of magnesium ribbon (Ar = 24.3) to 50.0 cm³ of 1.00 mol dm⁻³ hydrochloric acid in an insulated cup: Mg(s) + 2HCl(aq) → MgCl₂(aq) + H₂(g). The temperature rises by 13.8 °C. Take the specific heat capacity of the solution as 4.18 J g⁻¹ °C⁻¹ and its density as 1.00 g cm⁻³.
(a)
Calculate the energy transferred to the solution, in J, and the amount of magnesium in mol, and show that the acid is in excess.
[3 marks]
(b)
Calculate the enthalpy change of the reaction in kJ per mole of magnesium. The balance has an uncertainty of ±0.001 g in each of two readings and the thermometer has an uncertainty of ±0.2 °C in each of two readings. Calculate the percentage uncertainty in the mass of magnesium and in the temperature change, and state which measurement contributes more to the overall uncertainty.
[4 marks]
Total for question 7: 7 marks
8
Ethanol is made industrially by the hydration of ethene in the gas phase: C₂H₄(g) + H₂O(g) → C₂H₅OH(g). Mean bond enthalpies / kJ mol⁻¹: C=C 612; C–C 347; C–H 413; C–O 358; O–H 464. Standard enthalpy changes of formation / kJ mol⁻¹: C₂H₄(g) +52.0; H₂O(g) −241.8; C₂H₅OH(g) −235.3.
(a)
Calculate the enthalpy change for the hydration of ethene using the mean bond enthalpies. Compare your answer with the value calculated from the enthalpy changes of formation and explain any difference.
[6 marks]
(b)
Ethanol vapour burns to form carbon dioxide gas and water vapour. The standard enthalpy change of formation of carbon dioxide is −393.5 kJ mol⁻¹. Calculate the enthalpy change for burning one mole of ethanol vapour and the mass of ethanol (Mr = 46.0) that must burn to release 500 kJ.
[6 marks]
Total for question 8: 12 marks

End of questions

Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).