Thermal Physics for Singapore O-Level Physics (6091): the kinetic particle model of matter, temperature and thermometers, thermal expansion and specific heat capacity, and melting, boiling and latent heat

What this module covers

Thermal Physics in O-Level Physics (SEAB 6091) explains heat using a single picture: matter is made of particles in constant motion. From this kinetic particle model the module derives how temperature is defined and measured, why materials expand when heated, how much energy a temperature change needs, and why melting and boiling happen at constant temperature.

The model connects to gas pressure from the earlier module (faster particles hit the walls harder) and supplies the energy ideas reused throughout physics. Each dot point below has full worked answers and practice questions.

The kinetic particle model of matter

Kinetic particle model of matter describes solids, liquids and gases in terms of how their particles are arranged and how they move. Particles are closely packed and vibrate in a solid, are close but mobile in a liquid, and are far apart and fast in a gas. Heating raises the average kinetic energy of the particles, which we observe as a rise in temperature.

This single model underlies every other idea in the module, so understanding it well pays off repeatedly.

Temperature and thermometers

Temperature and thermometers defines temperature as a measure of how hot an object is, linked to the average kinetic energy of its particles, and distinguishes it from heat (total thermal energy). It explains how a liquid-in-glass thermometer works using thermal expansion and how fixed points (the ice point and steam point) calibrate the Celsius scale.

Thermal expansion and specific heat capacity

Thermal expansion and specific heat capacity explains expansion in terms of more energetic particles taking up more space, with gases expanding most and solids least. It also quantifies heating with

where $c$ is the specific heat capacity, the energy needed to raise one kilogram by one kelvin.

Melting, boiling and latent heat

Melting, boiling and latent heat explains the changes of state. During melting and boiling the temperature stays constant because the supplied energy, the latent heat, goes into breaking bonds between particles rather than raising their kinetic energy. The specific latent heat of fusion melts a solid, and the specific latent heat of vaporisation boils a liquid, each per kilogram.

How this module is examined

• Answer with the particle model. Explanations should describe particle arrangement, motion and energy, then link to the observation.
• Use $E = mc\Delta\theta$ carefully. Match units, and use the temperature change, not the temperature itself.
• Explain the flat parts of a heating curve. During a change of state the temperature is constant because energy breaks bonds, not raises kinetic energy.

Check your knowledge

Recall and calculation questions across the module. Try them, then check the worked solutions.

1. Describe the arrangement and motion of particles in a gas. (2 marks)
2. State the difference between heat and temperature. (2 marks)
3. Calculate the energy needed to raise $0.50\ \text{kg}$ of a metal by $40\,^{\circ}\text{C}$ if its specific heat capacity is $900\ \text{J kg}^{-1}\,^{\circ}\text{C}^{-1}$. (2 marks)
4. Explain why temperature stays constant while a pure solid is melting. (2 marks)
5. State which state of matter expands the most for a given temperature rise. (1 mark)