International A LevelChemistryEdexcelExam Questions4: Rates, Equilibria and Further Organic Chemistry4.4 Chemical Equilibria

Chemical Equilibria (Edexcel International A Level Chemistry)

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4.4 Chemical Equilibria

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4.4 Chemical Equilibria

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1a1 mark

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?

  • the mole fraction of carbon dioxide

  • the partial pressure of carbon monoxide

  • the rate of the backward reaction

  • the value of Kp for the forward reaction

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1b
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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?

  •  0.237

  • 0.263

  • 0.474

  • 0.526

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21 mark

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?

  • dm9 mol–3

  • dm6 mol–2

  • mol2 dm–6

  •  mol3 dm–9

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3a1 mark

The water gas reaction is used in the manufacture of hydrogen.

C (s) + H2O (g) ⇌ CO (g) + H2 (g)    ∆H to the power of ⦵= +131.2 kJ mol−1

a)
What is the equilibrium constant, Kc , for this reaction?

  • Kc = [CO][H2]

  • Kc = begin mathsize 16px style fraction numerator open square brackets C O close square brackets open square brackets H subscript 2 close square brackets over denominator open square brackets C close square brackets end fraction end style

  • Kc = begin mathsize 16px style fraction numerator open square brackets C O close square brackets open square brackets H subscript 2 close square brackets over denominator open square brackets H subscript 2 O close square brackets end fraction end style

  • Kc = fraction numerator open square brackets CO close square brackets open square brackets straight H subscript 2 close square brackets over denominator open square brackets straight H subscript 2 straight O close square brackets open square brackets straight C close square brackets end fraction

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3b1 mark
b)
What happens to the equilibrium constants of the forward and reverse reactions when the temperature is increased?

      Kc of forward reaction Kc of reverse reaction
  ☐ A increases increases
  ☐ B increases decreases
  ☐ C decreases increases
  ☐ D decreases decreases

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    1
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    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]

    • 3.61 × 10−5

    • 9.07 × 10−1

    • 9.66 × 10−1

    • 2.77 × 104

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