Particles

    OCR
    GCSE

    The particle model of matter postulates that all material consists of particles whose arrangement, motion, and energy define the physical states of solid, liquid, and gas. Candidates must quantify material properties using density calculations and analyze thermal processes through the concepts of internal energy, specific heat capacity, and specific latent heat. Mastery requires interpreting heating and cooling curves to identify state changes where temperature remains constant despite energy transfer, linking macroscopic observations to microscopic particle behavior.

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    Objectives
    4
    Exam Tips
    4
    Pitfalls
    4
    Key Terms
    5
    Mark Points

    What You Need to Demonstrate

    Key skills and knowledge for this topic

    • Award 1 mark for stating that mass is conserved during a change of state because the number of particles remains the same
    • Award 1 mark for describing gas particles as moving randomly with high speeds in all directions
    • Credit responses that define internal energy as the sum of the kinetic and potential energies of all particles in the system
    • Award 1 mark for calculating density correctly, including the correct unit conversion (e.g., g/cm³ to kg/m³)
    • Award 1 mark for explaining that during melting, energy supplied is used to overcome intermolecular forces rather than raise temperature

    Example Examiner Feedback

    Real feedback patterns examiners use when marking

    • "You correctly identified the state, but you need to describe the *movement* of the particles, not just their arrangement"
    • "Check your units for density—remember that 1 g/cm³ is not equal to 1 kg/m³"
    • "Good use of the term 'internal energy', but you must specify it includes both kinetic and potential energy stores"
    • "When explaining the flat section of the graph, explicitly state that energy is breaking bonds/overcoming forces, not increasing kinetic energy"

    Marking Points

    Key points examiners look for in your answers

    • Award 1 mark for stating that mass is conserved during a change of state because the number of particles remains the same
    • Award 1 mark for describing gas particles as moving randomly with high speeds in all directions
    • Credit responses that define internal energy as the sum of the kinetic and potential energies of all particles in the system
    • Award 1 mark for calculating density correctly, including the correct unit conversion (e.g., g/cm³ to kg/m³)
    • Award 1 mark for explaining that during melting, energy supplied is used to overcome intermolecular forces rather than raise temperature

    Examiner Tips

    Expert advice for maximising your marks

    • 💡When describing the motion of gases, the word 'random' is essential; 'moving quickly' alone often fails to secure the mark
    • 💡In density calculations, check the required units for the answer; if the question asks for kg/m³, ensure you convert mass to kg and volume to m³ before dividing
    • 💡For 6-mark questions on determining density, explicitly state the measuring instrument (e.g., 'measure mass using a top-pan balance', 'measure volume using a Eureka can')
    • 💡Remember that on a heating curve, a horizontal line indicates a change of state where Potential Energy increases but Kinetic Energy (temperature) remains constant

    Common Mistakes

    Pitfalls to avoid in your exam answers

    • Stating that individual particles expand or contract when heated, rather than the spaces between them increasing
    • Confusing 'boiling' (occurs at specific temperature throughout liquid) with 'evaporation' (occurs at surface at any temperature)
    • Believing that temperature increases during a change of state (melting/boiling) on a heating curve
    • Failing to convert volume units correctly, specifically calculating 1 m³ = 100 cm³ instead of 1,000,000 cm³

    Key Terminology

    Essential terms to know

    States of matter and kinetic theory
    Density determination and calculation
    Internal energy, specific heat capacity, and latent heat
    Gas pressure and temperature relationships

    Likely Command Words

    How questions on this topic are typically asked

    Calculate
    Explain
    Describe
    State
    Suggest
    Plot

    Practical Links

    Related required practicals

    • •{"code":"PAG P1","title":"Determination of Density","relevance":"Measuring density of regular/irregular solids and liquids"}
    • •{"code":"PAG P5","title":"Changes of State","relevance":"Investigating temperature changes during heating/cooling"}

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