Internal energy

    AQA
    GCSE

    Internal energy is defined as the sum of the total kinetic energy and potential energy of all particles that make up a system. Heating a system transfers energy to its particles, resulting in either an increase in temperature (kinetic store) or a change of state (potential store). Candidates must apply the particle model to explain these changes, distinguishing between the breaking of intermolecular bonds during phase changes and the increase in particle speed during heating. Quantitative analysis requires the application of the Specific Heat Capacity and Specific Latent Heat equations.

    0
    Objectives
    3
    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 defining internal energy as the total kinetic and potential energy of all particles in a system
    • Credit responses that link temperature increase to an increase in the kinetic energy of particles
    • Award marks for stating that during a change of state, internal energy increases due to potential energy gain while temperature remains constant
    • For calculations, award 1 mark for correct substitution into E = mL or E = mcΔθ and 1 mark for the correct final answer with units

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for defining internal energy as the total kinetic and potential energy of all particles in a system
    • Credit responses that link temperature increase to an increase in the kinetic energy of particles
    • Award marks for stating that during a change of state, internal energy increases due to potential energy gain while temperature remains constant
    • For calculations, award 1 mark for correct substitution into E = mL or E = mcΔθ and 1 mark for the correct final answer with units

    Examiner Tips

    Expert advice for maximising your marks

    • 💡Memorise the phrase 'sum of kinetic and potential energy of particles'—omitting 'potential' loses the mark
    • 💡On heating graphs, identify flat lines as changes of state (PE increases, KE constant) and sloped lines as heating (KE increases)
    • 💡Check units carefully: convert kJ to J before calculation, as constants are usually given in J/kg

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Defining internal energy only as kinetic energy, neglecting the potential energy stored in bonds between particles
    • Believing temperature increases during a change of state (e.g., boiling water gets hotter than 100°C)
    • Confusing Specific Heat Capacity (temperature change) with Specific Latent Heat (state change) when selecting equations

    Key Terminology

    Essential terms to know

    Likely Command Words

    How questions on this topic are typically asked

    Define
    Explain
    Calculate
    Describe
    Determine

    Practical Links

    Related required practicals

    • •{"code":"Required Practical 1","title":"Specific Heat Capacity","relevance":"Determination of c involves measuring energy input and temperature change, directly linking to internal energy concepts"}

    Ready to test yourself?

    Practice questions tailored to this topic