Lesson 10.1.1

10.1.1 Dynamic equilibrium and the equilibrium constant Kc Quiz: Pearson Edexcel Chemistry, Unit 10

20 questions

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Lesson 10.1.1, Dynamic equilibrium and the equilibrium constant Kc: 20 multiple choice questions for the Pearson Edexcel Chemistry (9CH0), Unit 10: Equilibrium I, written with Revision Ninja.

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The 20 questions

  1. What is meant by dynamic equilibrium in a closed system?

    • The reaction has stopped and no further change occurs, so the mixture is unchanged from that point
    • The concentrations of reactants and products are always equal, which is the defining feature
    • The reaction is complete and only products remain, because the reverse reaction has ceased
    • The forward and backward reaction rates are equal, and concentrations stay constant

  2. Which statement is true at dynamic equilibrium?

    • The reaction has no enthalpy change, because the energy of the reactants and products is identical
    • The rate of the forward reaction equals the rate of the backward reaction
    • The rate of the forward reaction is zero, because no net reaction can take place at equilibrium
    • The concentrations of reactants and products are equal, which is the defining property of equilibrium

  3. For the equilibrium N2(g) + 3H2(g) ⇌ 2NH3(g), which expression is correct for Kc?

    • Kc = [NH3]^2 / ([N2][H2]^3)
    • Kc = [NH3] / ([N2] + [H2]^3)
    • Kc = [NH3]^2 / ([N2][H2])
    • Kc = [N2][H2]^3 / [NH3]^2

  4. For the equilibrium H2(g) + I2(g) ⇌ 2HI(g), what are the units of Kc?

    • mol dm-3, the usual concentration units, because Kc is always defined as a concentration ratio
    • mol-1 dm3, the units produced when the reactant concentrations are multiplied together
    • No units, because the total moles of gas on each side are equal
    • mol2 dm-6, the units produced by squaring the product concentration in the expression

  5. For the equilibrium N2O4(g) ⇌ 2NO2(g), the equilibrium concentrations are [N2O4] = 0.040 mol dm-3 and [NO2] = 0.12 mol dm-3. What is Kc?

    • 0.36 mol dm-3
    • 3.0 mol dm-3
    • 0.0144 mol dm-3
    • 0.0048 mol dm-3

  6. In a heterogeneous equilibrium, how are solids and pure liquids treated in the expression for Kc?

    • They are included with their concentrations
    • They are omitted from the expression
    • They are squared in the expression
    • They are included as their molar masses

  7. For the equilibrium CaCO3(s) ⇌ CaO(s) + CO2(g), which expression is correct for Kc?

    • Kc = [CaCO3] / [CO2]
    • Kc = [CaO] / [CaCO3]
    • Kc = [CO2]
    • Kc = [CaO][CO2] / [CaCO3]

  8. In the equilibrium 2SO2(g) + O2(g) ⇌ 2SO3(g), what is the expression for Kc?

    • Kc = [SO3]^2 / ([SO2] + [O2])
    • Kc = [SO3] / ([SO2][O2])
    • Kc = [SO3]^2 / ([SO2]^2 [O2])
    • Kc = [SO2]^2[O2] / [SO3]^2

  9. What happens to the value of Kc when a catalyst is added to an equilibrium mixture?

    • It doubles
    • It increases with the amount of catalyst
    • It becomes zero
    • It does not change

  10. In the reaction of hydrogen with iodine, Kc is found to be 50 at 700 K. What does a large value of Kc indicate?

    • The reaction is catalysed
    • The reaction is at zero rate
    • The equilibrium lies to the left, favouring reactants
    • The equilibrium lies to the right, favouring products

  11. A reaction reaches equilibrium with [A] = 0.20 mol dm-3, [B] = 0.10 mol dm-3 and [C] = 0.50 mol dm-3, for A + B ⇌ C. What is Kc?

    • 0.04 mol-1 dm3
    • 0.4 mol-1 dm3
    • 2.5 mol-1 dm3
    • 25 mol-1 dm3

  12. For the equilibrium PCl5(g) ⇌ PCl3(g) + Cl2(g), at equilibrium [PCl5] = 0.020 mol dm-3, [PCl3] = 0.080 mol dm-3 and [Cl2] = 0.080 mol dm-3. What is Kc?

    • 0.0080 mol dm-3
    • 3.13 mol dm-3
    • 0.00200 mol dm-3
    • 0.32 mol dm-3

  13. Which statement describes the approach to dynamic equilibrium from pure reactants in a closed container?

    • The backward rate is high at the start and stays constant throughout the approach to equilibrium
    • Both rates are zero at the start and rise together until the equilibrium position is reached in the flask
    • The rates never change and are equal from the beginning, so there is no approach to equilibrium
    • The forward rate is initially high and falls, while the backward rate rises until they are equal

  14. What is the effect of adding more reactant to a system at equilibrium on the value of Kc?

    • Kc increases in proportion to the added reactant, so the constant rises as more reactant is supplied
    • Kc decreases in proportion to the added reactant, since more reactant pushes the value downward
    • Kc becomes equal to one whenever a reactant is added, because the mixture is then at standard state
    • Kc stays the same at constant temperature, though the position of equilibrium shifts

  15. Which expression is correct for the reaction 2NO(g) + O2(g) ⇌ 2NO2(g)?

    • Kc = [NO2]^2 / ([NO]^2 [O2])
    • Kc = [NO2]^2 / ([NO] + [O2])
    • Kc = [NO2] / ([NO][O2])
    • Kc = [NO]^2 [O2] / [NO2]^2

  16. A reaction has Kc = 4.0 mol-1 dm3 for A + B ⇌ C. If [A] = 0.50 and [B] = 0.50 mol dm-3, what is [C] at equilibrium?

    • 2.0 mol dm-3
    • 0.25 mol dm-3
    • 4.0 mol dm-3
    • 1.0 mol dm-3

  17. Which description correctly identifies a heterogeneous equilibrium?

    • Only one product is formed
    • Reactants and products are all in the same state
    • Reactants and products are in more than one physical state
    • Reactants and products are all solids

  18. Why is an equilibrium constant for a reaction at a given temperature constant, even as concentrations change?

    • Kc is always equal to the concentration of the product, so it changes as the product forms
    • Kc depends on the volume of the container alone, so it changes whenever the vessel is resized
    • Kc depends only on temperature, so it remains constant for a fixed temperature
    • Kc is the ratio of reactant masses, which never changes because the masses are conserved

  19. For the equilibrium 2A + B ⇌ 3C, which expression is correct for Kc?

    • Kc = [C]^3 / ([A]^2 [B])
    • Kc = [C] / ([A][B])
    • Kc = [C]^3 / ([A] + [B])
    • Kc = [A]^2 [B] / [C]^3

  20. For the equilibrium Fe3+(aq) + SCN-(aq) ⇌ FeSCN2+(aq), which expression is correct for Kc?

    • Kc = [Fe3+] / ([SCN-][FeSCN2+])
    • Kc = [FeSCN2+] / ([Fe3+] + [SCN-])
    • Kc = [FeSCN2+] / ([Fe3+][SCN-])
    • Kc = [Fe3+][SCN-] / [FeSCN2+]

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