Increasing the pressure of a gas (Physics only)

    AQA
    GCSE

    Doing work on a gas increases the internal energy of the gas and can cause an increase in the temperature of the gas. When a gas is compressed by an external force, energy is transferred mechanically to the kinetic energy stores of the gas particles. This results in the particles moving with greater velocity, which corresponds to a higher measured temperature. Candidates must distinguish this mechanical heating effect from thermal energy transfer and apply the particle model to explain the conversion of work into internal energy.

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    Objectives
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    Exam Tips
    3
    Pitfalls
    4
    Key Terms
    4
    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for stating that work is done on the gas (by the piston/force)
    • Award 1 mark for linking work done to an increase in the internal energy of the gas
    • Award 1 mark for stating that the average kinetic energy of the gas particles increases
    • Award 1 mark for concluding that increased kinetic energy results in an increase in temperature

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for stating that work is done on the gas (by the piston/force)
    • Award 1 mark for linking work done to an increase in the internal energy of the gas
    • Award 1 mark for stating that the average kinetic energy of the gas particles increases
    • Award 1 mark for concluding that increased kinetic energy results in an increase in temperature

    Examiner Tips

    Expert advice for maximising your marks

    • 💡Use the phrase 'work is done on the gas' explicitly; this is often a standalone marking point
    • 💡Ensure you distinguish between the cause of pressure (collisions with walls) and the cause of temperature (average kinetic energy)
    • 💡For Higher Tier, clearly sequence the energy transfer: Mechanical Work → Internal Energy Store → Kinetic Energy of Particles → Temperature

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Attributing the temperature rise solely to friction between the piston and the cylinder wall rather than work done on the gas particles
    • Confusing the increase in pressure (due to more frequent collisions) with the increase in temperature (due to higher speed collisions)
    • Stating that particles 'vibrate more' (incorrect for gases) instead of moving with greater speed

    Key Terminology

    Essential terms to know

    Likely Command Words

    How questions on this topic are typically asked

    Explain
    State
    Calculate
    Describe
    Suggest

    Practical Links

    Related required practicals

    • •{"code":"Demonstration","title":"Bicycle Pump / Fire Piston","relevance":"Demonstrates rapid compression leading to ignition or heat generation"}

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