levo

Particle Model

Pressure and volume of a fixed mass of gas

  • 3 things to know
  • Paper 2

Overview

Why compressing a fixed mass of gas at constant temperature raises its pressure and expanding it lowers the pressure, a blocked bicycle pump, the pressure × volume equation, and calculating new pressures, volumes and pressure factors.

What you need to know

Answer each one before you reveal it.

Your recallNot started
Key term

Explain why reducing the volume of a fixed mass of gas at constant temperature increases its pressure.

Key term

Explain why the pressure of a fixed mass of gas falls when the gas expands at constant temperature.

Key term

Explain why the average speed of the particles does not change when a gas is compressed at constant temperature.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Explain why reducing the volume of a fixed mass of gas at constant temperature increases its pressure.

    Model answer

    The particles have less space, so they strike the walls more often each second.

  2. 2

    State what happens to the rate at which particles collide with the walls when a fixed mass of gas expands at constant temperature.

    Model answer

    It falls, because the particles travel further between collisions with the walls.

  3. 3

    Explain why the pressure of a fixed mass of gas falls when the gas expands at constant temperature.

    Model answer

    Fewer collisions on each square metre of wall each second means a smaller average force per unit area.

  4. 4

    Explain why the average speed of the particles does not change when a gas is compressed at constant temperature.

    Model answer

    The temperature sets the average speed of the particles, and the temperature has been kept the same.

  5. 5

    The outlet of a bicycle pump is blocked and the plunger is pushed slowly halfway in. Describe what happens to the pressure of the trapped air.

    Model answer

    It roughly doubles, because the same number of particles is squeezed into half the volume.

  6. 6

    State the two quantities that must be kept constant for the pressure of a gas to be inversely proportional to its volume.

    Model answer

    The mass of gas and its temperature.

Other ways to work this

The same content, four other ways.

What is inside Levo

Six ways to work the same material.

1Closed book
2Open book
3Closed book

The 3-step method, run for you

Answer cold, learn it, then prove it stuck. Levo tracks the jump between your first attempt and your last.

Key Concepts of Physics
Motion and Forces
Conservation of Energy
Waves

Cram a whole paper in one sitting

Sort every topic into what you know and what you do not, then drill only the weak ones.

2.5 × = 9000 s.
360027001000

Blank Blitz makes facts automatic

Rapid timed gap-fills on the terms and numbers you need to recall without thinking.

ALength is measured in metres, with the symbol m.
BMass is measured in kilograms, symbol kg.
CTime is measured in seconds, symbol s.

Build It gets the exam shape right

Assemble a full-mark answer from its marking points, in the order an examiner wants them.

Watt means the unit of power, symbol W.
TrueFalse

Test It catches misconceptions

Spot the fault in a statement. The traps are the mistakes students actually make.

721941163128510

Brain Breaks between sessions

Short focus games to reset attention, so the next set lands better than the last.

Every question in Particle Model, on a schedule.

Attempt a question from memory, write the correct version, then attempt it again. Levo records the jump between your first attempt and your last, and brings each question back on the day you are due to forget it.

Or £46 a year, about £3.83 a month. Cancel anytime.