A Level Official Exam Material
FREE Past Paper Questions by Topic
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Unit 5: Transition Metals and
Organic Nitrogen Chemistry
Organic Nitrogen Chemistry
Topic 13: Chemical Equilibria
For A Level students only
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 .
The reaction shown is at equilibrium.
The forward reaction is endothermic.
C(s) + CO2(g) ↔ 2CO(g)
(a) Which will increase when the temperature is lowered? (1)
A the mole fraction of carbon dioxide
B the partial pressure of carbon monoxide
C the rate of the backward reaction
D the value of Kp for the forward reaction
(b) At 680 °C and 1 atm, 52.6 % of the molecules in the gas mixture are carbon monoxide.
What is the partial pressure of carbon dioxide, in atmospheres? (1)
A 0.237
B 0.263
C 0.474
D 0.526
(Total for question = 2 marks)
Q2. 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 .
The equation for the precipitation of lead(II) chloride is shown.
Pb2+(aq) + 2Cl– (aq) ↔ PbCl2(s)
What are the units of the equilibrium constant, Kc?
A dm9 mol–3
B dm6 mol–2
C mol2 dm–6
D mol3 dm–9
(Total for question = 1 mark)
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 .
The total entropy change, ΔStotal , of a reaction at 298 K is −85.0 J K −1 mol−1 .
What is the value of the equilibrium constant for this reaction at 298 K?
[R = 8.31 J mol−1 K −1 ]
A 3.61 × 10−5
B 9.07 × 10−1
C 9.66 × 10−1
D 2.77 × 104
(Total for question = 1 mark)
Q4. 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 the equilibrium decomposition of hydrogen iodide into hydrogen and iodine can be written in two ways.
Q5. Equal amounts of W and X are mixed and allowed to reach equilibrium.
The value of the equilibrium constant is Kc = 4.85.
At equilibrium, the mixture will contain
A almost all Y and Z
B almost all W and X
C W, X, Y and Z but there is less Y and Z than W and X
D W, X, Y and Z but there is more Y and Z than W and X
(Total for question = 1 mark)
Q6. 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 water gas reaction is used in the manufacture of hydrogen.
C(s) + H2O(g) ↔ CO(g) + H2(g) = +131.2 kJ mol−1
(a) What is the equilibrium constant, Kc, for this reaction?
Q7. Calcium oxide is manufactured by heating limestone at 1000 °C for 30 minutes.
The equation for the reaction is:
(a) The numerical value of the equilibrium constant for this reaction is increased by: (1)
A allowing the carbon dioxide to escape
B increasing the heating time
C increasing the temperature
D reducing the pressure
(b) Which is the correct expression for the equilibrium constant, Kc, for this reaction? (1)
Q8. 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 .
At 25 °C, the pH of pure water is 7.00 and at 100 °C, the pH of pure water is 6.14.
What can be deduced from this information?
Q9. Esters are used in flavourings and perfumes.
They can be made by reactions involving alcohols.
(a) A flask containing a mixture of 0.200 mol of ethanoic acid and 0.150 mol of ethanol was left at 25 °C, in the presence of a catalyst, until equilibrium had been established.
The ethanoic acid present in the equilibrium mixture required 34.8 cm3 of a 2.50 mol dm–3 solution of sodium hydroxide for complete neutralisation.
(i) Calculate the value of the equilibrium constant, Kc, for this reaction at 25 °C. (4)
(ii) The enthalpy change for this reaction is small.
Explain, by reference to the type and number of bonds being broken and made, how this might have been predicted. (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(ii) Explain one advantage and one disadvantage of using Reaction 2 rather than Reaction 1. (4) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(Total for question = 12 marks)
Q10. The reversible reaction between hydrogen chloride and oxygen produces water vapour and chlorine.
(a) Explain what effect, if any, each of the following changes has on the yield of chlorine at equilibrium and on the equilibrium constant, Kp .
(i) An increase in the total pressure (3) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(ii) An increase in the temperature (2) ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. ............................................................................................................................................. .............................................................................................................................................
(iii) The use of a catalyst (2)
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(b) 0.850 mol of hydrogen chloride was mixed with 0.600 mol of oxygen and allowed to reach equilibrium in a closed flask. At equilibrium the total pressure was 1.50 atm and there was 0.250 mol of chlorine in the flask.
(i) Complete the table. (3)
(ii) Write the expression for the equilibrium constant, Kp . (1)
(iii) Use your answers to (b)(i) and (b)(ii) to calculate the value for Kp.
Give your answer to an appropriate number of significant figures, and include units. (3)
(iv) Use your answer to (b)(iii) to calculate a value for the total entropy change of the reaction, ΔStotal. (2)
(c) Draw a sketch of entropy against temperature for water to illustrate the entropy changes as temperature increases, including when water changes state.
A scale is not required for the vertical axis (3)
Q11. This question is about sulfuric acid and its salts. (a) The manufacture of sulfuric acid involves the equilibrium 2SO2(g) + O2(g) 2SO3(g) ΔrH = −197 kJ mol−1 (i)
A catalyst of vanadium(V) oxide is used in this reaction.
State the effect, if any, of the catalyst on the value of the equilibrium constant, Kp . (1) ............................................................................................................................................. .............................................................................................................................................
(ii) The temperature used for this reaction in industry is 700 K.
Explain, in terms of the equilibrium constant and the equilibrium position, the effect of an increase in temperature on the equilibrium yield of sulfur trioxide. (2) ............................................................................................................................................. .............................................................................................................................................
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(iii) Write the expression for the equilibrium constant, Kp , for this equilibrium. State symbols are not required. (1)
(iv) A mixture of 2.00 mol of sulfur dioxide and 1.00 mol of oxygen is allowed to reach equilibrium at 5.00 atm pressure. 1.60 mol of sulfur trioxide is formed.
Calculate the value of Kp. Include units and give your answer to an appropriate number of significant figures. (4)
(Total for question = 8 marks)
Q12. (e) (i) Write the expression for the equilibrium constant, Kp, for this reaction, including the units, if any. (2)
(ii) In an experiment, 10 mol of N2O4(g) was placed in a closed container at 50 °C.
At equilibrium, 27% of the N2O4(g) had dissociated, and the pressure in the container was 4.0 atm.
Calculate the value of Kp at 50 °C. (4)
(iii) The total pressure is doubled to 8.0 atm. State the effect on Kp. (1) ............................................................................................................................................. .............................................................................................................................................
(iv) The total pressure is doubled to 8.0 atm at constant temperature.
Explain the change in the percentage dissociation of N2O4(g) by considering the effect on the partial pressures of NO2(g) and N2O4(g). (3)
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(Total for question = 10 marks)_
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