Topic 3 - Thermal Physics

Temperature (unit: ℃ or K)

A measure of the average kinetic energy (per particle) of a system.

Heat (unit: J)

Energy transfer due to a temperature difference.

Internal Energy (unit: J)

The total kinetic and potential energy of the system.
Note: For ideal gases, this energy is all kinetic

Heat capacity (unit: J K-1)

The amount of energy required to raise the temperature of a system by 1K

Specific Heat capacity (unit: J kg-1 K-1)

The amount of energy per unit mass required to raise the temperature of a given substance by 1K

Assumptions made for an ideal gas

1. The particles are in constant, random motion, only interacting through elastic collisions with each other and container walls.

2. A large number of identical particles with volumes negligible compared to the container volume.

3. Low density, which typically is the case for low pressure and high temperature

Specific latent heat of vaporization (unit: J kg-1)

The energy needed to convert one unit mass of liquid of a given substance to gas.

Specific latent heat of fusion (unit: J kg-1)

The energy needed to convert one unit mass of solid of a given substance to liquid.

Why temperature remains constant during state change

• Intermolecular bonds are formed during freezing

• Intermolecular PE decreases and difference transferred as heat

• Average KE of molecules does not decrease/change

• Temperature is related to average KE of molecules hence unchanged

Outline the difference between the molecular structure of a solid and a liquid 

• in solid state, nearest neighbour molecules cannot exchange places/have fixed positions/are closer to each other/have regular pattern/have stronger forces of attraction

• in liquid, bonds between molecules can be broken and re-form