A LevelChemistryCambridge (CIE)Exam Questions7. EquilibriaChemical Equilibria: Reversible Reactions & Dynamic Equilibrium

Chemical Equilibria: Reversible Reactions & Dynamic Equilibrium (Cambridge (CIE) A Level Chemistry): Exam Questions

Exam code: 9701

2 hours38 questions

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Chemical Equilibria: Reversible Reactions & Dynamic Equilibrium

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1
1 mark

Nitrogen dioxide and dinitrogen tetroxide exist in equilibrium.

2NO2 (g) ⇌ N2O4 (g) ∆H = −57 kJ mol−1

Which conditions give the greatest percentage of NO2 in the equilibrium mixture?

  • High pressure and high temperature

  • High pressure and low temperature

  • Low pressure and high temperature

  • Low pressure and low temperature

Choose your answer

2
1 mark

Sulfuric acid is manufactured via a series of reactions in the Contact process. The equation for the main stage of this process is shown.

2SO2 (g) + O2 (g) ⇌ 2SO3 (g) ∆H = −197 kJ mol−1

Which statement about this reaction is correct?

  • Iron is used as a catalyst.

  • Increased temperature gives a higher equilibrium amount of SO2.

  • Increased temperature gives a higher yield of SO3.

  • Increased pressure gives a higher equilibrium amount of SO2.

Choose your answer

3
1 mark

Which statement describes a dynamic equilibrium?

  • The rate of the forward reaction is equal to the reverse reaction in a closed system, and the concentrations of the reactants and products are equal.

  • The rate of the forward reaction is equal to the reverse reaction in a closed system, and the concentrations of the reactants and products are constant.

  • The rate of the forward reaction is equal to the reverse reaction, and the concentrations of the reactants and products are constant.

  • The rate of reaction changes in either direction to counteract a change in conditions.

Choose your answer

4
1 mark

An equilibrium is set up in a closed container between equal amounts, in mol, of gaseous reactants A and B to form a gaseous product C.

The total pressure within the container at 50 °C is 3.0 atm.

A (g) + B (g) ⇌ 2C (g)

The equilibrium partial pressure of A at 50 °C is 0.50 atm.

What is the partial pressure of C, in atm, in the equilibrium mixture?

  • 1.0

  • 1.5

  • 2.0

  • 2.5

Choose your answer

5
1 mark

The Haber process is used to produce ammonia from nitrogen and hydrogen on an industrial scale. The diagram below represents the Haber process. 

Process flow diagram of ammonia synthesis showing N₂ and H₂ feed, heat exchanger, catalytic converter, condenser and NH₃ product stream with recycle lines

What is the purpose of the heat exchanger?

  • To cool the reaction products and separate ammonia from unreacted nitrogen and hydrogen.

  • To warm the incoming gas mixture to increase the yield of ammonia.

  • To warm the incoming gas mixture to increase the rate of reaction.

  • To cool the incoming gas mixture to prevent overheating the catalyst.

Choose your answer

6
1 mark

Ethanol is manufactured by reacting steam with ethene.

C2H4 (g) + H2O (g) ⇌ C2H5OH (g) ΔH = −45 kJ mol−1

Which pair of changes would both increase the equilibrium yield of ethanol?

  • Catalyst added; pressure increased

  • Catalyst added; temperature decreased

  • Pressure increased; temperature decreased

  • Pressure decreased; temperature increased

Choose your answer

7
1 mark

Propyl ethanoate is formed in an esterification reaction. How can the value of the equilibrium constant Kc be increased?

CH3COOH (l) + C3H7OH (l) ⇌ CH3COOC3H7 (l) + H2O (l) ΔH = −10 kJ mol−1

  • Adding a catalyst

  • Decreasing the temperature

  • Increasing the pressure

  • Increasing the temperature

Choose your answer

8
1 mark

Gaseous iodine reacts with hydrogen to establish an equilibrium at 450 °C.

H2 (g) + I2 (g) ⇌ 2HI (g) ΔH = −9 kJ mol−1

colourless + purple ⇌ colourless

Which change in conditions will cause the purple colour of the gas mixture to become paler?

  • Decrease in pressure

  • Decrease in temperature

  • Increase in pressure

  • Increase in temperature

Choose your answer

9
1 mark

For the equilibrium 2A (g) +  B (g)  ⇌  2C (g)  ∆H = +6.5 kJ mol-1, what will change the value of Kp?

  • Adding a catalyst

  • Decreasing the pressure

  • Increasing the pressure

  • Increasing the temperature

Choose your answer

10
1 mark

An equilibrium is established in the reaction.

AB (aq) + CD (aq) ⇌ AC (aq) + BD (aq) ΔH = +180 kJ mol−1

Which factor would affect the value of Kc in this equilibrium?

  • Change in pressure in the presence of a catalyst

  • Change in temperature

  • Increasing the concentration of AB (aq)

  • Increasing the concentration of AC (aq)

Choose your answer

11
1 mark

Ammonia is manufactured using the Haber process, which is represented by the following equation:

N2 (g) + 3H2 (g) ⇌ 2NH3 (g) ΔH = −93 kJ mol−1

What happens to the rates of the forward and reverse reactions when the temperature is increased?

Rate of forward reaction

Rate of reverse reaction

A

no change

no change

B

no change

increases

C

increases

increases

D

increases

no change

    Choose your answer

    1
    1 mark

    At 450℃  the value for Kc for the below reaction is 60.

    H2 (g) + I2 (g)  ⇌  2HI (g)

    The equilibrium moles of H2 and I2 are 2 mol and 0.3 mol, respectively. 

     How many moles of HI (g) is present at equilibrium? 

    • 0.010

    • 0.10

    • 6

    • 36

    Choose your answer

    2
    1 mark

    Ethyne and hydrogen are formed from methane, and a dynamic equilibrium is established. 

    2CH4 (g)  ⇌  3H2 (g) + C2H2 (g)

    What are the units for Kc?

    • mol-2 dm6

    • mol dm-3

    • mol2 dm-6

    • mol3 dm-9

    Choose your answer

    3
    1 mark

    Upon heating, dinitrogen tetroxide will dissociate into nitrogen dioxide. 

    N2O4 (g)  ⇌  2NO2 (g) 

    At a particular temperature, the equilibrium partial pressure of nitrogen dioxide was 0.67 atm and dinitrogen tetroxide 0.33 atm.

    What is the numerical value of Kp at this temperature?

    • 0.49

    • 0.74

    • 1.36

    • 2.03

    Choose your answer

    4
    1 mark

    Nitrogen monoxide and oxygen can be formed from the thermal decomposition of nitrogen dioxide.

    2NO2 (g) ⇌ 2NO (g) + O2 (g)

    In an experiment 4 mol of nitrogen dioxide were put into a 1 dm3 container and heated to a constant temperature. The equilibrium mixture contains 0.8 mol of oxygen.

    Which expression gives the value of the equilibrium constant, Kc, at the temperature of the experiment?

    • fraction numerator 0.8 squared cross times 0.8 over denominator 4 squared end fraction

    • fraction numerator 1.6 cross times 0.8 over denominator 2.4 squared end fraction

    • fraction numerator 1.6 squared cross times 0.8 over denominator 2.4 end fraction

    • fraction numerator 1.6 squared cross times 0.8 over denominator 2.4 squared end fraction

    Choose your answer

    5
    1 mark

    The Contact process is used for the industrial production of sulfuric acid. The three main chemical reactions involved in the Contact process are listed below.

    S (s) + O2 (g) → SO2 (g)

    SO2 (g) + ½O2 (g) ⇌ SO3 (g)

    SO3 (g) + H2O (l) → H2SO4 (l)

    Which statement about this process is correct?

    • In the first stage, a large excess of air under high pressure is used to improve the yield.

    • Two of the three stages are equilibria.

    • All three stages are exothermic.

    • In the final stage, SO3 is absorbed by water droplets.

    Choose your answer

    6
    1 mark

    The dissociation of gas X2Y4 into XY2 is represented in the equation below.

    X2Y4 (g) ⇌ 2XY2 (g) ΔHθ = +60 kJ mol−1

    At constant pressure, the temperature of the equilibrium mixture is increased. Which statement correctly explains the change in volume of the gas mixture?

    • The volume increases because the equilibrium shifts to the right only.

    • The volume increases because the equilibrium shifts to the right and because of thermal expansion.

    • The volume remains unchanged because thermal expansion is exactly counteracted by a leftward shift of equilibrium.

    • The volume decreases because a leftward shift of equilibrium more than counteracts thermal expansion.

    Choose your answer

    7
    1 mark

    A compound WX dissociates into X− and W+ ions in solution, as shown by the equation below.

    WX (aq) ⇌ X− (aq) + W+ (aq)

    0.40 mol of WX is dissolved in 2.0 dm3 of solution and heated to a constant temperature until equilibrium is established. The equilibrium mixture contains 0.10 mol of W+.

    Which expression correctly represents Kc for this equilibrium?

    • fraction numerator 0.05 over denominator 0.15 end fraction

    • fraction numerator 0.05 squared over denominator 0.15 end fraction

    • fraction numerator 0.1 squared over denominator 0.3 end fraction

    • fraction numerator 0.15 over denominator 0.05 squared end fraction

    Choose your answer

    8
    1 mark

    Ammonia is produced from hydrogen and nitrogen in the Haber process. 

    N2 (g) + 3H2 (g)  ⇌  2NH3 (g)

    A mixture of 2.00 mol of nitrogen, 3.00 mol of hydrogen and 1.98 mol of ammonia is allowed to reach equilibrium in a sealed container with a volume of 1 dm3 under certain conditions. It was found that 1.64 mol of ammonia were present in the equilibrium mixture.

    What is the value of Kc under these conditions?

    • 0.0287

    • 0.0498

    • 0.101

    • 0.215

    Choose your answer

    9
    1 mark

    5.00 mol of A and 5.00 mol of B are placed in a sealed vessel of volume 1 dm3 at a constant total pressure of 1.50 atm. An equilibrium is established, containing 3.00 mol of C.

    A (g) + B (g) ⇌ 2C (g)

    What is the equilibrium partial pressure of A?

    • 0.350 atm

    • 0.525 atm

    • 0.750 atm

    • 2.00 atm

    Choose your answer

    1
    1 mark

    A dynamic equilibrium was set up between carbon monoxide, hydrogen and methanol in a 2 dm3 sealed vessel at a constant temperature.

    CO (g) + 2H2 (g) ⇌ CH3OH (g)

    The equilibrium moles of each gas were: CO = 6.20 × 10-3 mol, H2 = 4.80 × 10-3 mol, CH3OH = 5.20 × 10-5 mol.

    Where has the equilibrium shifted and what is the value of Kc?

    Direction of shift

    Kc

    A

    right

    364

    B

    left

    364

    C

    left

    1456.1

    D

    right

    1456.1

      Choose your answer

      2
      1 mark

      Gaseous reactants A and B are placed in a 5 dm3 container and heated until equilibrium is reached. 1.0 mol of each reactant is used, and 10% of A has reacted at equilibrium.

      A (g) + 3B (g) ⇌ 2C (g)

      What is the equilibrium concentration of C?

      • 0.02 mol dm-3

      • 0.04 mol dm-3

      • 0.18 mol dm-3

      • 0.20 mol dm-3

      Choose your answer

      3
      1 mark

      Four molecules of oxygen can bind to one molecule of haemoglobin, Hb, according to the following equation.

      Hb (aq) + 4O2 (aq)  ⇌  Hb (O2)4 (aq)

      At equilibrium, the concentration of oxygen is 6.7 x 10-6 mol dm-3 and the equilibrium concentrations of Hb and Hb(O2)4 are the same. 

      What is the value of Kc for this equilibrium?

      • 2 × 10-21 mol-4 dm12

      • 6.7 × 10-6 mol-4 dm12

      • 1.5 × 105 mol-4 dm12

      • 5 × 1020 mol-4 dm12

      Choose your answer

      4
      1 mark

      An aqueous solution was prepared containing 1.0 mol of silver nitrate and 1.0 mol of iron(II) sulfate in a 2.00 dm3 container. When equilibrium was established, the mixture contained 0.44 mol of silver ions.

      Ag+ (aq) + Fe2+ (aq) ⇌ Ag (s) + Fe3+ (aq)

      What is the numerical value of Kc for this equilibrium?

      • 0.173

      • 1.27

      • 2.89

      • 5.79

      Choose your answer

      5
      1 mark

      560 kg of nitrogen and 120 kg of hydrogen are pressurised, heated and passed over an iron catalyst.

      N2 (g) + 3H2 (g) ⇌ 2NH3 (g)

      When the mixture of gases reaches equilibrium, it contains 96.0 kg of hydrogen. What mass, in g, of ammonia does the equilibrium mixture contain?

      • 1.36 × 102

      • 1.36 × 105

      • 2.04 × 105

      • 2.72 × 105

      Choose your answer

      6
      1 mark

      The percentage yield of ammonia in the Haber process is plotted against operating pressure for two temperatures, 400 °C and 500 °C.

      N2 (g) + 3H2 (g) ⇌ 2NH3 (g) ΔH = −92 kJ mol−1

      Which diagram correctly represents the relationship between yield and pressure at these two temperatures?

      • Graph showing % NH3 at equilibrium increasing with pressure (0–20 × 10³ kPa); 400 °C curve (dashed) lies above 500 °C curve (solid) at all pressures
      • Graph showing % NH3 at equilibrium increasing with pressure (0–20 × 10³ kPa); 500 °C curve (solid) lies above 400 °C curve (dashed) at all pressures
      • Graph showing % NH3 at equilibrium decreasing with pressure (0–20 × 10³ kPa); 400 °C curve (dashed) lies above 500 °C curve (solid) at all pressures
      • Graph showing % NH3 at equilibrium decreasing with pressure (0–20 × 10³ kPa); 500 °C curve (solid) lies above 400 °C curve (dashed) at all pressures

      Choose your answer

      7
      1 mark

      Shown below are two equilibria.

      The numerical value for Kc in reaction 1 is 2.

      Reaction 1 2A2 (g) + B2 (g) ⇌ 2A2B (g)

      Reaction 2 A2B (g) ⇌ A2 (g) + ½B2 (g)

      At the same temperature, what is the numerical value of Kc for reaction 2?

      • 1 half

      • fraction numerator 1 over denominator square root of 2 end fraction

      • 1

      • 4

      Choose your answer