Lesson 9.2.2

9.2.2 Kinetic theory and the ideal gas equation Quiz: Pearson Edexcel Physics, Unit 9

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 9.2.2, Kinetic theory and the ideal gas equation: 20 multiple choice questions for the Pearson Edexcel Physics (9PH0), Unit 9: Thermodynamics, written with Revision Ninja.

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The 20 questions

  1. In kinetic theory, a gas exerts pressure on a container wall because

    • gravity pushes the gas against the wall, and molecules only follow the pull
    • the wall heats the molecules, which then expand and push back on the wall
    • molecules strike the wall and change momentum, exerting a force on it
    • molecules attract the wall and pull it outward, which holds the gas in place

  2. In pV = NkT, what is the unit of k?

    • J K^-1
    • W K^-1
    • J mol^-1
    • J kg^-1 K^-1

  3. What is the relationship between the molar gas constant R and the Boltzmann constant k?

    • R = k / N_A, where N_A is the Avogadro constant
    • R equals k exactly, since both constants describe a single mole of gas
    • R = N_A k, where N_A is the Avogadro constant
    • R = k^2 N_A, which links the gas constant to the square of the constant

  4. Which assumption is made about molecules of an ideal gas?

    • They have negligible volume and exert no forces on each other except during collisions.
    • They attract each other strongly at all separations, which holds the gas together at low pressure.
    • They are at rest between collisions with the container walls, so kinetic energy is zero.
    • They all have exactly the same speed at every instant, so the gas moves as one body.

  5. Which pressure against volume plot shows an isothermal change of a fixed mass of ideal gas?

    • A straight line of p against T with positive gradient
    • A straight line of V against T passing through zero
    • A straight line through the origin of p against V
    • A straight line through the origin of p against 1/V

  6. The result (1/2) m <c^2> = (3/2) kT links temperature to which quantity?

    • the mean speed of the molecules only
    • the pressure of the gas alone
    • the mean square speed of the molecules
    • the potential energy of the gas

  7. A gas of 3.0 x 10^23 molecules at 300 K occupies 0.020 m^3. What is its pressure? Use k = 1.38 x 10^-23 J K^-1.

    • 6.2 x 10^4 Pa
    • 1.2 x 10^6 Pa
    • 6.2 x 10^2 Pa
    • 3.1 x 10^4 Pa

  8. At 1.0 x 10^5 Pa and 300 K, a gas occupies 0.0249 m^3. How many moles are present? Use R = 8.31 J mol^-1 K^-1.

    • 0.10 mol
    • 10 mol
    • 1.0 mol
    • 2.5 mol

  9. A fixed mass of ideal gas is compressed isothermally to half its original volume. How does its pressure change?

    • It stays the same.
    • It halves.
    • It quadruples.
    • It doubles.

  10. A gas of density 1.2 kg m^-3 has pressure 1.0 x 10^5 Pa. What is its root-mean-square speed?

    • 250 m s^-1
    • 2.0 x 10^2 m s^-1
    • 500 m s^-1
    • 1.2 x 10^3 m s^-1

  11. What is the mean translational kinetic energy per molecule of an ideal gas at 400 K?

    • 2.1 x 10^-21 J
    • 1.4 x 10^-23 J
    • 5.5 x 10^-21 J
    • 8.3 x 10^-21 J

  12. A fixed volume of gas has its absolute temperature raised from 300 K to 450 K. What is the ratio of final to initial pressure?

    • 1.0
    • 1.5
    • 2.0
    • 0.67

  13. How many molecules are in 0.50 mol of gas? Use N_A = 6.02 x 10^23 mol^-1.

    • 1.2 x 10^24
    • 6.0 x 10^22
    • 3.0 x 10^23
    • 6.0 x 10^23

  14. A gas at 2.0 x 10^5 Pa and 300 K is heated at constant volume to 450 K. What is its pressure?

    • 2.0 x 10^5 Pa
    • 4.5 x 10^5 Pa
    • 3.0 x 10^5 Pa
    • 1.3 x 10^5 Pa

  15. If the number of molecules and the volume are both doubled while the temperature is held constant, what happens to the pressure?

    • It halves.
    • It doubles.
    • It quadruples.
    • It is unchanged.

  16. If the number of molecules is doubled at fixed volume and temperature, what happens to the pressure?

    • It quadruples.
    • It doubles.
    • It stays the same.
    • It halves.

  17. Why is the mean square speed, rather than the mean speed, used in the pressure equation?

    • Pressure and kinetic energy depend on the average of c squared, so faster molecules count more.
    • The mean speed of gas molecules is always zero, so it cannot be used in any pressure calculation.
    • Squared speeds give the mass of each molecule directly, which the pressure formula needs.
    • The mean speed can only be measured for liquids, which is why gases need a different method.

  18. Which quantity does NOT appear in the ideal gas equation pV = NkT?

    • volume
    • number of molecules
    • temperature
    • mass of each molecule

  19. Real gases deviate from ideal behaviour most at

    • high pressure and low temperature, where intermolecular forces and molecular volume matter
    • low pressure and low temperature, where collisions are perfectly elastic and brief
    • low pressure and high temperature, where molecules are far apart and move freely
    • high pressure and high temperature, where molecules move fastest and collide most

  20. A gas contains N molecules, each with mean square speed <c^2>, in a volume V at pressure p. Which expression is correct?

    • p = N m <c^2> / (3V)
    • p = N m <c^2> / (2V)
    • p = 3 N m <c^2> / V
    • p = N m <c> / (3V)

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