O-Level and SEC G3 Physics K323
P9: Thermal Properties of Matter
Relate temperature, internal energy, heat capacity, and latent heat with correct units and phase-change reasoning.
Reviewed for the 2027 cohort on 19 July 2026. The official syllabus remains authoritative for assessable wording and paper details.
Core notes
Thermal properties separate temperature from internal energy and distinguish heating that changes temperature from heating that changes state. Cooling curves link the energy model to observable temperature-time behaviour.
Internal energy and heat capacity
Internal energy is the sum of random particle kinetic energy and potential energy associated with particle interactions. Temperature relates to average kinetic energy, so two objects at the same temperature need not have the same internal energy.
Heat capacity is energy required per degree change for a whole object. Specific heat capacity is energy required per kilogram per degree change. A larger mass or larger specific heat capacity needs more energy for the same temperature rise.
Changes of state and latent heat
During melting or boiling at constant pressure, energy transfer changes particle potential energy and arrangement rather than average kinetic energy, so temperature remains constant during the phase change.
Specific latent heat is energy per unit mass for a change of state without temperature change. Boiling occurs throughout a liquid at its boiling temperature, while evaporation occurs at the surface and can happen below the boiling temperature.
Cooling curves
A cooling curve plots temperature against time. Sloping regions show temperature change within a state. A flat or less-steep phase-change region shows energy release while the substance changes state.
Real curves may not be perfectly flat because of impurities, changing heat-loss rate, thermometer lag or supercooling. Interpret the physical process rather than forcing an ideal shape onto all data.
Formulae and relationships
| Relationship | Use |
|---|---|
| Find energy for a temperature change. | |
| Find energy for a change of state. | |
| Find heat capacity of a whole object. |
Worked examples
Example 1: How much energy heats of water by if ?
- Use .
- Substitute .
- The temperature interval has the same numerical size in kelvin and degrees Celsius.
Answer: .
Chapter checkpoint
Use these three moves to organise the topic before attempting a mixed or practical question.
- Distinguish temperature, internal energy, heat capacity, and specific heat capacity.
- Treat melting and boiling as energy transfers at constant temperature during the phase change.
- Use specific latent heat with the correct mass and phase-change boundary.
Official outcome coverage
K323 P9: 9 mapped outcomes, references P9(a), P9(b), P9(c), P9(d), P9(e), P9(f), P9(g), P9(h), P9(i). Check the official K323 syllabus.
The outcome wording is not reproduced here. The relevant official syllabus remains authoritative for exact assessable scope.
Practical and data connection
Obtain a heating or cooling curve, identify phase-change regions, and discuss heat loss and thermometer lag as limitations.
Exam traps and retrieval check
Avoid these traps
- Using during a constant-temperature phase change.
- Confusing heat capacity of an object with specific heat capacity per kilogram.
- Saying no energy transfers during a flat phase-change region.
Check from memory
Why is temperature constant during melting?
Transferred energy changes particle potential energy and arrangement rather than average kinetic energy.
Where does evaporation occur?
At the liquid surface, potentially below boiling temperature.
What determines the gradient of a real cooling curve?
Heat capacity, surroundings, temperature difference, surface conditions and phase behaviour.
Pure versus Combined scope
This is a standalone Pure Physics K323 topic. It has no matching top-level Combined Physics owner in K326 or K327, so Combined students should not add it unless their current syllabus or school scope explicitly requires it.
Shared explanation source
Eclat has a related explanation in its existing IP library. It can help with the shared concept, but its IP extensions and school-sensitive scope are not automatically part of K323. Open the related IP explanation.