Thermal physics

Internal energy

The sum of the kinetic and potential energies of its particles:

U = 3/2 x NkT

U = 3/2 x nRT

U = ½ x Nmc²

Isothermal change

A change that takes place at constant temperature

Isobaric change

A change that takes place at constant pressure

Isochoric change

A change that takes place at constant volume

Energy flows (Work)

W = p x change in volume

Energy flows (Heat)

Transit of energy from a higher temperature to a region of lower temperature.

Once it reaches thermal equilibrium there is no need heat flow between them.

First law of thermodynamics

Chang in U = Q - W

Q : heat flow into the system

W : work done by the system

Rapid expansion of an ideal gas

During this process, it doesn’t allow time for heat to flow into the system therfore:

U = -W

Slow (isothermal) expansion of an ideal gas

In this process heat will have time to flow into the system. The gas temperature won’t be able to fall more than slightly below its surroundings, therefore:

U = 0

Q = W

Volume of solids and liquids

Compared with gases, solids and liquids change their volume very little. The work done in these sytems are negligible, therefore:

U = Q

Specific heat capacity

Heat required per kg to raise a systems temperature by 1 kelvin.