iGCSE Physics (0625)-Unit 2. Thermal physics-2.1.2 Molecular model- Paper 4

Question

(a)       In terms of the momentum of molecules, explain how a gas exerts pressure on the walls of its container.        [4]

(b) A fixed mass of gas of volume V1 is at a pressure p1. It is compressed to a volume V2.

    1. Complete the equation for the final pressure p2 of the gas when the gas is compressed at constant temperature.

      p2 =                                                                                                                                                              [2]

    2. State and explain how the final pressure compares with p2 when the temperature of the gas increases during compression.

        statement …………………………………………………………………………………………………………..

        explanation …………………………………………………………………………………………………………    [3]

                                                                                                                                                                                  [Total: 9]

    Answer/Explanation

    Ans:

    (a)

    molecules strike walls

    momentum (of molecules) changes / momentum = mass× velocity

    force = rate of change of momentum

    pressure = (sum of) force(s) / area / pressure = rate of change of momentum / area

    (b)

    (i)

    (p2=)p1V1 / V2

    p1V1 =p2V2 )

    (ii)

    greater
    molecules move faster / have greater KE / molecules have greater momentum
    (leads to) more frequent / harder collisions (with walls) / great rate of change of momentum