SEC G3 Combined Science Physics component K326/K327
CP7: Kinetic Particle Model of Matter
Explain states, temperature, internal energy, and phase changes using particle spacing, motion, and forces.
Reviewed for the 2027 cohort on 19 July 2026. The official syllabus remains authoritative for assessable wording and paper details.
Core notes
The kinetic particle model explains bulk properties by connecting them to particle spacing, motion, and interaction.
States and their properties
A solid keeps shape and volume because its particles are closely packed in an ordered arrangement, held by strong attractive forces, and vibrate about fixed positions. A liquid keeps its volume but changes shape because closely packed particles remain attracted yet can move past one another. A gas fills its container because widely separated particles have negligible attractions and move freely.
Explanations must connect the visible property to particle arrangement, movement, separation, and forces rather than saying only that particles are different.
Temperature and particle energy
A temperature rise means the particles have greater average kinetic energy. It does not mean every particle has exactly the same kinetic energy.
Internal energy is the total random kinetic energy of the particles plus the potential energy associated with their interactions.
Changes of state
During melting or boiling, energy enters while temperature remains constant because the particle arrangement and interaction energy change. During solidification or condensation, energy leaves at constant temperature.
Do not describe particles as melting, expanding, or becoming a new substance. The state changes while the particles remain the same substance.
Formulae and relationships
This chapter is assessed mainly through models, field patterns and explanations. Build the causal chain before adding any calculation.
Worked examples
Example 1: Why can ice at its melting point absorb energy without becoming warmer?
- Identify the process as melting.
- The added energy changes particle arrangement and potential energy.
- Average kinetic energy, and therefore temperature, stays constant during the change.
Answer: The transfer changes the state rather than raising the average particle kinetic energy.
Chapter checkpoint
Use these three moves to organise the topic before attempting a mixed or practical question.
- Explain states using particle spacing, motion, forces, and arrangement.
- Connect temperature to average particle kinetic energy without saying particles expand.
- Explain a phase change through energy transfer and particle separation while temperature remains constant.
Official outcome coverage
K326 CP7: 5 mapped outcomes, references CP7(a), CP7(b), CP7(c), CP7(d), CP7(e). Check the official K326 syllabus.
K327 CP7: 5 mapped outcomes, references CP7(a), CP7(b), CP7(c), CP7(d), CP7(e). Check the official K327 syllabus.
The outcome wording is not reproduced here. The relevant official syllabus remains authoritative for exact assessable scope.
Practical and data connection
Record a heating or cooling curve and distinguish sloping regions from constant-temperature phase-change regions. Keep sample quantity and heating rate controlled, stir when appropriate, and explain thermometer lag and energy transfer to the surroundings.
Exam traps and retrieval check
Avoid these traps
- Drawing gas particles as larger particles.
- Equating temperature with total internal energy.
- Claiming temperature rises throughout melting.
Check from memory
Why does a liquid flow?
Its close particles can move past one another.
What particle quantity rises with temperature?
Average kinetic energy.
What two contributions make internal energy?
Random kinetic energy and interaction potential energy.
Official Combined Science scope
This shared Combined Physics owner serves both K326 and K327. The three states, the kinetic particle model, temperature, internal energy, and constant-temperature phase changes.