Thermal Properties of Matter

Topic-by-topic explanations

1. Introduction

Thermal properties explain how temperature and energy transfer affect matter, including expansion and changes of state.

2. Temperature and heat

Temperature describes thermal state; heat is energy transferred because of a temperature difference. Heat moves spontaneously from hotter to colder objects until thermal equilibrium is reached.

3. Measurement of temperature

Thermometers use a property that changes predictably with temperature, such as liquid volume, electrical resistance or thermoelectric voltage. Celsius and Kelvin are related by T(K)=t(°C)+273.15.

4. Ideal-gas equation and absolute temperature

For a fixed amount of ideal gas, pV=nRT. Gas-law calculations use absolute temperature in kelvin; at fixed volume p/T is constant.

5. Thermal expansion

Linear expansion is ΔL=αLΔT and volume expansion is ΔV=γVΔT. For isotropic solids and small temperature changes, γ≈3α; restraint can create thermal stress.

6. Specific heat capacity

Specific heat capacity c is heat required per unit mass per unit temperature rise. When there is no phase change, Q=mcΔT; heat capacity of an object is C=mc.

7. Calorimetry

Calorimetry applies energy conservation: heat lost by hotter bodies equals heat gained by colder bodies in an insulated system. Include the container's heat capacity when relevant.

8. Change of state

During melting, freezing, boiling or condensation, energy mL is absorbed or released while temperature remains constant at the transition pressure.

9. Heat transfer

Conduction transfers energy through interactions, convection by bulk motion of fluids, and radiation through electromagnetic waves. Radiation can travel through vacuum.

10. Newton's law of cooling

Newton's law of cooling approximates cooling rate as proportional to the excess temperature over surroundings for small differences and similar conditions.

Formula sheet

Use SI units, state assumptions, show your working and check units before finalising an answer.

Worked example

Common errors and revision checklist

Use kelvin in gas-law ratios. Use latent heat during phase change, and include all bodies in the calorimetry energy balance.

• Write the governing law before substituting values.
• Show units and signs/directions.
• Check whether assumptions are satisfied.