A LevelPhysicsAQAExam QuestionsFurther Mechanics & Thermal PhysicsMolecular Kinetic Theory Model

Molecular Kinetic Theory Model (AQA A Level Physics): Exam Questions

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Molecular Kinetic Theory Model

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11 mark

Six molecules are travelling with the directions and speeds shown in the diagram below.

6-6-mcq-q1-easy-aqa-a-level-physics

What is the root–mean–square–speed of these molecules?

  • 283 m s–1

  • 342 m s–1

  • 685 m s–1

  • 831m s–1

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21 mark

The average mass of an air molecule is 4.2 × 10–26 kg

What is the mean square speed of an air molecule at 850 K?

  • 647 m2 s–2

  • 743 m2 s–2

  • 4.19 × 105 m2 s–2

  • 8.38× 105 m2 s–2

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31 mark

The equation for the kinetic theory model, pV =1 thirdNm(crms)2 is given on the data and formula sheet. 

Which of the following statements is not a valid assumption when deriving this equation?

  • The collisions between gas molecules and the walls of a container are inelastic

  • Attractive forces between molecules are negligible

  • The duration of a collision is negligible compared with the time between collisions

  • The volume of the molecules is negligible compared with the volume of the gas

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41 mark

Pollen grains are placed in a transparent illuminated box and water is added.  The pollen grains are seen to move randomly on the surface of the water when viewed with a microscope. 

What is the cause of the random motion of the pollen grains?

  • The pollen grains are moving randomly due to their temperature

  • The pollen grains are moving due to convection currents caused by the water being heated by the light

  • The pollen grains absorb light energy and gain kinetic energy

  • The pollen grains collide with the water molecules

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51 mark

The equation for the kinetic energy of a gas molecule is given below: 

         1 halfmopen parentheses C subscript r m s end subscript close parentheses squared = 3 over 2kT

What does open parentheses C subscript r m s end subscript close parentheses squared represent?

  • The sum of the squares of the speeds of the gas molecules

  • The average of the square of the speeds of the gas molecules

  • The average speed of the gas molecules 

  • The root–mean–square speed of the gas molecules

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11 mark

The gas argon has a density of 1.80 kg m–3.  When it is at a temperature of 350 K it exerts a pressure of 1.00 × 105 Pa. 

What is the root–mean–square speed of argon molecules?

  • 224 m s–1

  • 408 m s–1

  • 671 m s–1

  • 1340 m s–1

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21 mark

What is the total internal energy of 3.2 mol of an ideal gas which has a temperature of 25 °C?

  • 1000 J

  • 7200 J

  • 8000 J

  • 12 000 J

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31 mark

Which of the graphs below shows the correct relationship between the mean square speed of a molecule in a gas, open parentheses C subscript r m s end subscript close parentheses squared , and its temperature in degrees Celsius?

6-6-mcq-q4-medium-aqa-a-level-physics

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    41 mark

    A sample of air contains oxygen, and nitrogen molecules.  An oxygen molecule is heavier than a nitrogen molecule. 

    Which row in the table below correctly compares the magnitude of the kinetic energy and mean–square speed of the oxygen and nitrogen molecules? 

     

    Magnitude of kinetic energy of oxygen and nitrogen molecules

    Magnitude of mean–square speed of oxygen and nitrogen molecules

    A

    B

    C

    D

    equal

    equal

    not equal

    not equal

    equal

    not equal

    equal

    not equal

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      11 mark

      An ideal gas is initially at a temperature of 500°C.  It is heated so that the root mean square velocity of the gas molecules is doubled. 

      What are the values for the temperature of the gas and the mean kinetic energy of the gas molecules after the gas has been heated?

       

      Temperature /°C

      Kinetic Energy /J

      A

      B

      C

      D

      1273

      1546

      2819

      3092

      3.20 × 10–20

      3.20 × 10–20

      6.40 × 10–20

      6.40 × 10–20

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        21 mark

        The diagram below shows a single molecule of mass 4.6 × 10–26 kg moving with a speed of 500 m s–1 in a rigid cubical container.  The length of the side of the container is 0.25 m. 

        6-6-mcq-q2-hard-aqa-a-level-physics

        What is the average pressure exerted on the wall by the molecule?

        You may assume that the collisions between the molecule and the walls are perfectly elastic.

        • 3.7 × 10–25 Pa

        • 7.4 × 10–25 Pa

        • 3.7 × 10–19 Pa

        • 7.4 × 10–19 Pa

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        31 mark

        Air can be taken to consist of 80% nitrogen molecules and 20% oxygen molecules.  Nitrogen has a relative molecular mass of 28 and oxygen has a relative molecular mass of 32. 

        What is the ratio of the root mean square speed of nitrogen molecules to that of oxygen molecules in the air?

        • 0.25

        • 0.50

        • 1.07

        • 1.20

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        41 mark

        On a day when the atmospheric pressure is 102 kPa and the temperature is 10°C, the pressure in a car tyre is 190 kPa above atmospheric pressure.  After a long journey the temperature of the air in the tyre rises to 30 °C. 

        What is the percentage increase in the root–mean–square speed of the molecules of air as a result of this journey ? 

        Assume that no air is lost from the tyres.

        • 3.5 %

        • 96.5 %

        • 103.5 %

        • 107 %

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        51 mark

        When an ideal gas stored in a sealed container with a fixed volume the root–mean–square speed of the molecules is c m s–1. The temperature of the gas is changed so that the pressure of the gas inside the container is halved. 

        Which expression below gives the correct root–mean–square speed of the molecules after the temperature is changed? 

        • begin mathsize 16px style square root of 2 end stylec

        • c over 4

        • c over 2

        • fraction numerator c over denominator square root of 2 end fraction

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