A Level Official Exam Material
FREE Past paper Questions by Topic
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Unit 2: Energetics, Group Chemistry,
Halogenoalkanes and Alcohols
Halogenoalkanes and Alcohols
Topic 6: Energetics
For both AS and A Level students
Q1. For each question, select one answer from A to D and put a cross in the box .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .
Which are correct for the reaction shown?
CH3COOH + KOH → CH3COO−K + + H2O
ΔH = –55.8 kJ mol−1
Q2. Answer the question with a cross in the box you think is correct .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .
The standard enthalpy change of neutralisation for the reaction between sodium hydroxide solution and hydrochloric acid is –56 kJ mol–1 .
Which row in the table is correct for this neutralisation?
Q3. Answer the question with a cross in the box you think is correct .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .
Which is the correctly labelled reaction profile for an exothermic reaction?
Q4. Answer the questions with a cross in the boxes you think are correct .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .
The diagram shows a reaction profile for a reversible reaction.
(a) Which symbol represents the enthalpy change for the reaction R → P? (1) A u B v C w D x
(b) Which symbol represents the activation energy of the reaction P → R? (1)
A u
B v
C w
D x
(c) Hess's Law can be applied to this system.
Which expression is correct? (1)
A v + x = u + w
B w + x = u
C u – w = v
D u – v = x
(Total for question = 3 marks)
Q5. Answer the question with a cross in the box you think is correct .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .
Which equation represents the standard enthalpy change of atomisation of bromine?
Q6. Under certain conditions, graphite burns to form carbon monoxide.
2C(s) + O2(g) → 2CO(g) ΔH = −221 kJ mol−1.
Which of these is correct?
Q7. Answer the question with a cross in the box you think is correct .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .
The equation for a reaction is 2C(s) + O2(g) → 2CO(g)
Which is the correct symbol for the enthalpy change for this reaction?
Q8. Answer the question with a cross in the box you think is correct .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .
In an experiment, 50.0 cm3 of 1.0 mol dm−3 HCl(aq) reacts with 50.0 cm3 of 1.0 mol dm−3 NaOH(aq).
The energy released = 2500 J. The specific heat capacity of the mixture is 4.18 J g−1 °C−1
What temperature change occurs in the reaction?
A an increase of 6.0°C
B a decrease of 6.0°C
C an increase of 12.0°C
D a decrease of 12.0°C
(Total for question = 1 mark)
Q9. For each question, select one answer from A to D and put a cross in the box .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .
5.20 g of sodium hydrogencarbonate is added to an excess of acid.
The temperature increases and the energy change is calculated to be 1030 J.
What is the enthalpy change per mole of sodium hydrogencarbonate?
[Mr NaHCO3 = 84.0]
A –12.3 kJ mol−1
B –16.6 kJ mol−1
C –63.8 kJ mol−1
D –16 600 kJ mol−1
(Total for question = 1 mark)
Q10. Zinc metal reacts with copper(II) sulfate solution.
The equation for the reaction is: Zn(s) + CuSO4(aq) → ZnSO4(aq) + Cu(s) ΔrH = −210 kJ mol–1 .
(a) What is the temperature rise, in °C, when excess zinc powder is added to 50 cm3 of copper(II) sulfate solution containing 0.0025 mol of copper(II) ions?
[Assume the specific heat capacity of the solution is 4.2 J g–1 °C–1 ]. (1)
A 2.5
B 10.5
C 25.0
D 44.1
(b) The reaction of zinc with copper(II) sulfate is best classified as: (1)
A disproportionate
B neutralisation 5
C redox
D thermal decomposition
(Total for question = 2 marks)
Q11. Answer the question with a cross in the box you think is correct .
If you change your mind about an answer, put a line through the box and then mark your new answer with a cross .
The bond enthalpy for the Cl—Cl bond is +243.0 kJ mol–1 .
What is the enthalpy change of atomisation of chlorine in kJ mol–1?
A +243.0
B –243.0
C +121.5
D –121.5
(Total for question = 1 mark)
Q12. Major volcanic eruptions, such as the one in Indonesia in 1815, eject large amounts of ash and gases into the atmosphere.
The gases include carbon dioxide, water vapour, hydrogen chloride and sulfur dioxide.
(c) (i) During a volcanic eruption, hydrogen chloride gas is also released into the upper atmosphere, which in turn produces some chlorine free radicals.
Chlorine free radicals react with ozone: Derive the overall equation for this reaction of ozone.
State symbols are not required. (1)
(ii) Give two reasons why the presence of a small number of chlorine free radicals in the upper atmosphere causes a large decrease in the amount of ozone. (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(ii) Sulfur trioxide reacts with water to produce sulfuric acid.
SO3(g) + H2O(l) → H2SO4(aq)
ΔrH = −200 kJ mol−1
Draw an enthalpy level diagram to show the enthalpy change for this reaction. (2)
(iii) Droplets of sulfuric acid are formed when sulfur trioxide reacts with water in the upper atmosphere.
These droplets reflect ultraviolet radiation from the Sun back into space.
In the volcanic eruption in Indonesia in 1815, large amounts of both carbon dioxide and sulfur dioxide were released.
During the following year, there were global low temperatures.
Assess the effect of both gases on global temperatures after the volcanic eruption. (3) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(Total for question = 8 marks)
Q13. Magnesium reacts with sulfuric acid in an exothermic reaction.
(a) Write an equation for the reaction. Include state symbols in your answer. (2)
(b) A student carried out an experiment to determine the enthalpy change of the reaction.
A sample of 0.50 g of magnesium powder was added to 25 cm3 of 0.20 mol dm−3 sulfuric acid.
Calculate the number of moles of magnesium and of sulfuric acid that reacted. Justify your answer. (3) ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(c) (i) The results obtained are given in the table. Plot the results on the grid.
(d) Calculate the standard molar enthalpy change for the reaction, using your answers to (b) and (c)(ii).
Include a sign and units in your answer.
[Specific heat capacity of solution = 4.18 J g–1 °C–1 ] (4)
(Total for question = 13 marks)
Q14. (a) Silver ions have anti-microbial properties and are used in some wound dressings.
Silver nitrate can be made by warming a mixture of silver metal and concentrated nitric acid.
(b) Two students used different methods to determine the concentration of a silver nitrate solution.
(i) Student A used a calorimetric method, reacting a 50.0 cm3 sample of the solution with excess powdered zinc.
The student recorded a maximum rise in temperature of 5.2 °C.
Calculate the concentration of the silver nitrate solution in mol dm–3 .
[Assume the specific heat capacity of the solution is 4.18 J g–1 °C–1 and the density of the solution is 1.00 g cm–3 .] (3)
(ii) Student B used a gravimetric method, which involved weighing a product of a reaction.
A 50.0 cm3 sample of the same silver nitrate solution was mixed with excess potassium bromide solution.
The precipitate was filtered and weighed.
The mass of the precipitate was found to be 5.96 g.
Calculate the concentration of the silver nitrate solution, in mol dm–3 , from this gravimetric method. (2)
(iii) The students' values were different from the data book value.
Student A's value was lower and student B's value was higher.
Give a possible reason for each difference. (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(Total for question = 7 marks)
Q15. This question is about enthalpy changes.
(a) An experiment was carried out to determine the enthalpy change of combustion for ethanol.
C2H5OH(l) + 3O2(g) → 2CO2(g) + 3H2O(l) 1.19 g of ethanol was burned in a spirit burner.
The heat energy from this combustion raised the temperature of 100 g of water from 21.6 °C to 63.9 °C. (i) Calculate the number of moles of ethanol in 1.19 g.
[Molar mass of ethanol = 46.0 g mol−1 ] (1)
(ii) Calculate the heat energy required to raise the temperature of 100 g of water from 21.6 °C to 63.9 °C.
[Specific heat capacity of water = 4.18 J g−1 °C−1 ] (2)
(iii) Use your answers to (a)(i) and (ii) to calculate a value for the enthalpy change of combustion of ethanol.
Give your answer to an appropriate number of significant figures and include a sign and units. (3)
Q24. Biobutanol is a possible alternative to bioethanol as an additive to petrol.
(b) (i) Complete the equation for the combustion of butan-1-ol. State symbols are not required.
(ii) Calculate a value for the enthalpy change of combustion of butan-1-ol using the equation in (b)(i) and the mean bond enthalpies in the table.
(iii) A data book value of the molar enthalpy change of combustion of butan-1-ol is −2670 kJ mol−1
Give two reasons for the difference between this value and the value calculated in (b)(ii). (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(c) Biobutanol has some advantages over bioethanol.
(i) The combustion of bioethanol releases 23 MJ dm−3 compared to petrol which releases 32 MJ dm−3 .
Calculate the energy released in MJ dm−3 for the combustion of biobutanol.
If you need the markscheme, including the examiners' reports for each question, and more exam and teaching materials on this topic, contact me through the contact page