Lesson 3.1.10

3.1.10 Equilibrium constant Kp for homogeneous systems (A-level Quiz: AQA Chemistry, Unit 1

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.1.10, Equilibrium constant Kp for homogeneous systems (A-level: 20 multiple choice questions for the AQA Chemistry (7405), Unit 1: Physical chemistry, written with Revision Ninja.

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The 20 questions

  1. What is the partial pressure of a gas in a mixture?

    • The mole fraction of the gas multiplied by the total pressure of the mixture
    • The total pressure of the mixture divided by the mole fraction of the gas
    • The number of moles of the gas multiplied by the volume of the container
    • The pressure exerted by the gas alone in its own container at the same temperature

  2. What is the mole fraction of a component in a gas mixture?

    • The moles of that component divided by the moles of the other gases only
    • The moles of that component divided by the total moles of all gases in the mixture
    • The mass of that component divided by the total mass of the mixture
    • The volume of that component divided by the total volume of the container

  3. For 2SO2(g) + O2(g) <=> 2SO3(g), which is the correct expression for Kp?

    • Kp = p(SO3) / (p(SO2) x p(O2))
    • Kp = p(SO3)^2 / (p(SO2)^2 x p(O2))
    • Kp = p(SO2)^2 x p(O2) / p(SO3)^2
    • Kp = p(SO3)^2 x p(SO2)^2 / p(O2)

  4. In a gas mixture with total pressure 200 kPa, the mole fraction of NH3 is 0.25. What is the partial pressure of NH3?

    • 800 kPa
    • 50 kPa
    • 0.25 kPa
    • 200 kPa

  5. At equilibrium for PCl5(g) <=> PCl3(g) + Cl2(g), the partial pressures are p(PCl5) = 0.50, p(PCl3) = 0.20 and p(Cl2) = 0.20 atm. What is Kp?

    • 0.08 atm
    • 0.40 atm
    • 1.2 atm
    • 2.5 atm^-1

  6. A mixture at a total pressure of 100 kPa contains 1 mol H2, 1 mol I2 and 2 mol HI at equilibrium for H2 + I2 <=> 2HI. What is Kp?

    • 4
    • 0.25
    • 2
    • 8

  7. For N2O4(g) <=> 2NO2(g), what is the value of Kp when p(N2O4) = 0.80 atm and p(NO2) = 0.40 atm?

    • 0.50 atm
    • 5.0 atm
    • 0.20 atm
    • 2.0 atm

  8. What are the units of Kp for N2(g) + 3H2(g) <=> 2NH3(g) when pressures are in kPa?

    • No units, because Kp is always a pure number
    • kPa^-4
    • kPa^-2
    • kPa^2

  9. For H2(g) + I2(g) <=> 2HI(g), what are the units of Kp?

    • kPa^-1, because the number of moles of product is one more than the number of moles of reactant in the balanced equation
    • No units, because the number of gas moles is the same on both sides
    • atm^2, because the pressure of hydrogen iodide appears squared in the expression while the other gases appear once
    • kPa^2, because the partial pressures of the two reactants are multiplied together to give the units of the constant

  10. Which expression is the correct Kp for 2A(g) + B(g) <=> C(g)?

    • Kp = p(A)^2 x p(B) / p(C)
    • Kp = p(C)^2 / (p(A) x p(B))
    • Kp = p(A) x p(B) / p(C)
    • Kp = p(C) / (p(A)^2 x p(B))

  11. A reaction is exothermic in the forward direction. How does increasing temperature change the value of Kp?

    • Kp increases, because the catalyst is more active at higher temperature
    • Kp decreases, because the equilibrium shifts towards the reactants
    • Kp is unchanged, because only pressure can change an equilibrium constant
    • Kp increases, because the equilibrium shifts towards the products

  12. Why is the value of Kp for a reaction changed only by a change in temperature?

    • Temperature changes the total pressure at fixed volume, and the constant then changes by exactly that pressure change
    • Temperature changes the mole fraction of each gas in the mixture, so the constant changes by the same factor for all
    • Temperature changes the rate of both directions unequally, which changes the equilibrium position and the value of the constant
    • Temperature changes the total number of gas moles in the vessel, which changes the value of the constant directly

  13. Which change does NOT alter the value of Kp for a gas-phase equilibrium?

    • Changing the total pressure of the system by changing the volume, which always changes the value of the constant
    • Adding a catalyst, which changes the rate of attainment but not the value of the constant
    • Changing the temperature of the system, which always changes the value of the constant for every reaction at once
    • Changing the amount of one reactant so that the equilibrium shifts, which always changes the value of the constant

  14. For a reversible reaction at equilibrium at constant temperature, what happens to Kp if the total pressure is doubled by reducing the volume?

    • Kp halves, because the equilibrium shifts towards the reactants
    • Kp becomes zero, because the partial pressures cannot both be maintained
    • Kp doubles, because the total pressure doubles
    • Kp is unchanged, although the equilibrium position may shift

  15. At 1 atm total pressure, 0.5 mol of N2O4 dissociates for N2O4 <=> 2NO2 from 1 mol start, reaching a total pressure of 2.0 atm. What is Kp?

    • 0.67 atm
    • 2.67 atm
    • 5.33 atm
    • 1.33 atm

  16. A student says adding an inert gas at constant volume changes the value of Kp for a gas equilibrium. Which evaluation is correct?

    • Correct, because the inert gas reacts with the products and so changes the equilibrium constant
    • Partly correct, because the inert gas only changes Kp if the reaction is endothermic
    • Correct, because the inert gas raises the total pressure, which always changes Kp for any equilibrium
    • Incorrect, because the partial pressures of the reacting gases are unchanged and Kp depends only on temperature

  17. A gas mixture has a total pressure of 150 kPa and contains 0.60 mol of gas X out of 1.20 mol in total. What is the partial pressure of X?

    • 150 kPa
    • 75 kPa
    • 30 kPa
    • 0.5 kPa

  18. For N2(g) + 3H2(g) <=> 2NH3(g), which is the correct expression for Kp?

    • Kp = p(NH3) / (p(N2) x p(H2)^3)
    • Kp = p(NH3)^2 / (p(N2) x p(H2)^3)
    • Kp = p(N2) x p(H2)^3 / p(NH3)^2
    • Kp = p(NH3)^2 / (p(N2) x p(H2))

  19. For an endothermic gas equilibrium, what happens to the value of Kp when the temperature is raised?

    • Kp is unchanged, because temperature affects only the rate of reaction
    • Kp becomes zero, because the reactants are used up at high temperature
    • Kp increases, because the equilibrium shifts towards the products
    • Kp decreases, because the equilibrium shifts towards the reactants

  20. Which description of the equilibrium constant Kp for a gas-phase equilibrium is correct?

    • The partial pressure of the product only, measured at the end of the reaction, raised to its stoichiometric coefficient
    • A ratio of product partial pressures to reactant partial pressures, each raised to its coefficient, at constant temperature
    • A ratio of total pressure to the number of moles of gas present at equilibrium, each raised to its coefficient
    • A ratio of reactant concentrations to product concentrations, expressed in mol dm^-3 and raised to its coefficient

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