Lesson 3.6.2.3

3.6.2.3 Molecular kinetic theory model Quiz: AQA Physics, Unit 6

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson 3.6.2.3, Molecular kinetic theory model: 20 multiple choice questions for the AQA Physics (7408), Unit 6: Further mechanics and thermal physics (A-level only), written with Revision Ninja.

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The 20 questions

  1. Brownian motion of smoke particles is evidence for atoms because:

    • the particles move erratically due to unbalanced collisions with much smaller air molecules
    • the particles are stationary when observed microscopically
    • the particles move only because of gravity
    • the particles move in straight lines because of convection

  2. In the kinetic theory model of an ideal gas, collisions of molecules with the container walls are:

    • absent
    • perfectly elastic
    • inelastic, losing kinetic energy each time
    • perfectly inelastic

  3. A gas exerts pressure on its container because:

    • gas molecules are at rest
    • molecules attract the walls strongly
    • molecules repel only each other
    • molecules change momentum when they collide with the walls, giving a force per unit area

  4. The kinetic theory equation for an ideal gas of N molecules of mass m in volume V is:

    • pV = (1/2) N m c_rms
    • pV = 3 N m c_rms^2
    • pV = (1/3) N m c_rms^2
    • pV = N m c_rms

  5. The average kinetic energy of a molecule of an ideal gas is related to temperature by:

    • (3/2) kT
    • 2 kT
    • kT
    • (1/2) kT

  6. For an ideal gas the internal energy is:

    • zero at all temperatures
    • the sum of chemical bond energies
    • the potential energy of the molecules only
    • the kinetic energy of the atoms

  7. Which assumption is NOT made in the kinetic theory model of an ideal gas?

    • molecules attract each other strongly
    • collisions are elastic
    • the volume of molecules is negligible compared with the container
    • molecules move in random directions

  8. Take an ideal gas (N2, molar mass 0.028 kg mol^-1) at 300 K. Estimate its rms speed (R = 8.31 J K^-1 mol^-1).

    • about 1040 m s^-1
    • about 2700 m s^-1
    • about 520 m s^-1
    • about 260 m s^-1

  9. A gas has N = 1.0 x 10^23 molecules, each of mass 4.0 x 10^-26 kg, and rms speed 500 m s^-1. Its volume is 0.050 m^3. What is its pressure?

    • 6.7 x 10^3 Pa
    • 6.7 x 10^4 Pa
    • 3.3 x 10^3 Pa
    • 1.7 x 10^2 Pa

  10. If the absolute temperature of an ideal gas doubles, the mean kinetic energy of its molecules:

    • doubles
    • is unchanged
    • halves
    • quadruples

  11. Find c_rms for a molecule of mass 4.8 x 10^-26 kg at 300 K (k = 1.38 x 10^-23 J K^-1).

    • about 250 m s^-1
    • about 1000 m s^-1
    • about 130 m s^-1
    • about 510 m s^-1

  12. Which observation provides evidence for atoms through Brownian motion?

    • pollen grains settling steadily under gravity
    • erratic motion of pollen grains in water caused by unequal bombardment by water molecules
    • pollen grains stopping when water is cooled to zero
    • pollen grains moving only in straight lines

  13. At constant volume and temperature, doubling the number of molecules in a gas:

    • doubles the pressure
    • quadruples the pressure
    • leaves the pressure unchanged
    • halves the pressure

  14. A gas has 2.0 x 10^24 molecules at 300 K in a volume of 0.020 m^3 (k = 1.38 x 10^-23 J K^-1). What is its pressure?

    • about 8.3 x 10^3 Pa
    • about 4.1 x 10^5 Pa
    • about 1.0 x 10^5 Pa
    • about 4.1 x 10^3 Pa

  15. The rms speed of gas molecules at a fixed temperature, when the absolute temperature is quadrupled, becomes:

    • unchanged
    • double
    • quadruple
    • halve

  16. At the same temperature, compared with molecules of mass m, molecules of mass m/4 have a mean square speed that is:

    • the same
    • four times greater
    • four times smaller
    • twice as great

  17. Helium-like molecules of mass 6.6 x 10^-27 kg, number 2.0 x 10^23, rms speed 1200 m s^-1, fill 0.010 m^3. Estimate the pressure.

    • about 1.9 x 10^5 Pa
    • about 2.1 x 10^4 Pa
    • about 6.3 x 10^3 Pa
    • about 6.3 x 10^4 Pa

  18. A gas of 3.0 x 10^23 molecules at 300 K has total translational kinetic energy of about:

    • 3.7 kJ
    • 0.62 kJ
    • 620 J
    • 1.9 kJ

  19. A student says the gas laws prove kinetic theory. Which response is best?

    • Correct: the kinetic model was tested only after the gas laws were derived from it.
    • The gas laws are empirical; the kinetic model is a theory that explains them, and the laws alone do not prove the model.
    • Correct: the gas laws are derived directly from the kinetic model, so they prove it.
    • Incorrect: the gas laws are unrelated to molecular behaviour.

  20. Why does the kinetic model predict that gas pressure increases with temperature at constant volume?

    • higher temperature means greater molecular kinetic energy and faster wall collisions, so more force per unit area
    • molecules stick to the walls more strongly at higher temperature
    • higher temperature increases the number of molecules, raising pressure
    • molecules expand as temperature rises, pushing harder on the walls

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