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DP IB Physics: SL

Topic Questions

Home / IB / Physics: SL / DP / Topic Questions / 3. Thermal Physics / 3.2 Modelling a Gas / Structured Questions


3.2 Modelling a Gas

Question 1a

Marks: 2

This question is about a monatomic ideal gas.

(a)
Outline what is meant by an ideal monatomic gas.
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    Key Concepts
    Real & Ideal Gases

    Question 1b

    Marks: 4
    (b)
    Neon gas is kept in a container of volume 7.1 × 10–2 m3, temperature 325 K and pressure 3.7 × 105 Pa.

     

    (i)
    Calculate the number of moles of neon in the container.

    [2]

    (ii)
    Calculate the number of atoms in the gas.

    [2]

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      Key Concepts
      Ideal Gas Equation

      Question 1c

      Marks: 4
      (c)
      The volume of the gas is increased to 4.2 × 10–2 m3 at a constant temperature.

       

      (i)
      Calculate the new pressure of the gas in Pa

      [2]

      (ii)
      Explain this change in pressure, in terms of molecular motion.

      [2]

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        Question 1d

        Marks: 3

        Energy is supplied to the gas at a rate of 10 J s–1 for 10 minutes. The specific heat capacity of neon is 904 J kg–1 K–1 and its atomic mass number is 21. The volume of the gas does not change.

        (d)
        Determine the new pressure of the gas.
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          Key Concepts
          Ideal Gas Laws

          Question 2a

          Marks: 2

          This question is about an ideal gas in a container.

          An ideal gas is held in a glass gas syringe.

          (a)
          Calculate the temperature of 0.726 mol of an ideal gas kept in a cylinder of volume 2.6 × 10–3 m3 at a pressure of 2.32 × 105 Pa.
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            Key Concepts
            Ideal Gas Equation

            Question 2b

            Marks: 2
            (b)
            The average kinetic energy of the gas is directly proportional to one particular property of the gas.

             

            (i)
            Identify this property.

            [1]

            (ii)
            Calculate the average kinetic energy, E with minus on top, per molecule of the gas.

             [1]

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              Question 2c

              Marks: 4

              Energy is supplied to the gas at a rate of 0.5 J s–1 for 4 minutes. The specific heat capacity of the gas is 519 J kg–1 K–1.

              (c)
              Calculate the change in kinetic energy per molecule of the gas.
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                Question 2d

                Marks: 2

                The gas is heated until its temperature doubles.

                (d)
                Determine the factor the average speed of the molecules increases by.
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                  Question 3a

                  Marks: 2

                  This question is about the specific heat capacity of an ideal gas.

                  (a)
                  Outline two assumptions made in the kinetic model of an ideal 
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                    Key Concepts
                    Real & Ideal Gases

                    Question 3b

                    Marks: 5

                    Xenon–131 behaves as an ideal gas over a large range of temperatures and pressures.

                    (b)
                    One mole of Xenon–131 is stored at 20 °C in a cylinder of fixed volume. The Xenon gas is heated at a constant rate and the internal energy increased by 450 J. The new temperature of the Xenon gas is 41.7 °C.
                     
                    (i)
                    Define one mole of Xenon.

                    [1]

                    (ii)
                    Calculate the specific heat capacity of gaseous Xenon–131.

                    [2]

                    (iii)
                    Calculate the average kinetic energy of the molecules of Xenon at this new temperature.

                    [2]

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                      Question 3c

                      Marks: 4

                      The volume of the sealed container is 0.054 m3.

                      (c)
                      Calculate the change in pressure of the gas due to the energy supplied in part (b).
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                        Key Concepts
                        Ideal Gas Equation

                        Question 3d

                        Marks: 2

                        One end of the container is replaced with a moveable piston. The piston is compressed until the pressure of the container is 67000 Pa.

                        (d)
                        Determine the new volume of the container.
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                          Key Concepts
                          Ideal Gas Laws

                          Question 4a

                          Marks: 2

                          This question is about an experiment to investigate the variation in the pressure p of an ideal gas with changing volume V.

                          The gas is trapped in a cylindrical tube of radius 0.5 cm above a column of oil.

                          q4_modelling-a-gas_ib-sl-physics-sq-medium

                          The pump forces the oil to move up the tube and so reduces the volume of the gas. The scientist measures the pressure p of the gas and the height H of the column of gas.

                          (a)
                          Calculate the volume of the gas when the height is 1 cm.
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                            Key Concepts
                            Mole Calculations

                            Question 4b

                            Marks: 3

                            When the system is at a constant temperature of 20 °C, the pressure is 9600 Pa.

                            (b)
                            Calculate:
                             
                            (i)
                            the amount of moles of gas trapped in the cylinder

                            [2]

                            (ii)
                            the average kinetic energy of the molecules of trapped gas
                            [1]
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                              Question 4c

                              Marks: 3

                              The scientist plots their results of p against 1 over H on a graph.

                              (c)
                              Explain the shape of the graph and why this is to be expected.
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                                Key Concepts
                                Ideal Gas Equation

                                Question 4d

                                Marks: 3
                                (d)
                                When conducting the experiment, the scientist waits for a period of time between taking each reading.
                                 
                                (i)
                                Explain the reason for waiting this short period of time.

                                [1]

                                (ii)
                                Describe what will happen to the shape of the graph if the scientist does not wait a sufficient period of time between readings. 

                                [2]

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                                  Key Concepts
                                  Investigating Gas Laws

                                  Question 5a

                                  Marks: 2
                                  (a)
                                  State the Pressure law of ideal gases.
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                                    Key Concepts
                                    Ideal Gas Laws

                                    Question 5b

                                    Marks: 3

                                    The pressure exerted by an ideal gas containing 9.7 × 1020 molecules in a container of volume 1.5 × 10–5 m3 is 2.8 × 105 Pa.

                                    (b)
                                    Calculate the temperature of the gas in the container in °C.
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                                      Question 5c

                                      Marks: 3

                                      The pressure of the gas is measured at different temperatures whilst the volume of the container and the mass of the gas remain constant.

                                      qu-5c-figure-1

                                      (c)
                                      On the grid, sketch a graph to show how the pressure varies with the temperature.
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                                        Key Concepts
                                        Ideal Gas Laws

                                        Question 5d

                                        Marks: 3

                                        The container described in part (a) has a release valve that allows gas to escape when the pressure exceeds 3.5 × 105 Pa.

                                        (d)
                                        Calculate the number of gas molecules that escape when the temperature of the gas is raised to 380°C.
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