9-Thermal Physics Notes

Thermal Physics

Ideal Gas is one which obeys the ideal gas equation pV = nRT, where p is the pressure of the gas, V is the volume of the gas, n is the number of moles of the gas molecules, T is its absolute temperature and R = 8.31 J K-1 mol-1

Kinetic Theory of Gases - the basic assumptions:

- Gases consist of a very large number of atoms/molecules in continuous random motion. –
- All collisions are perfectly elastic.
- The duration of collision is negligible compared with time interval between collisions.
- Intermolecular forces are negligible except during a collision.
- The volume of the all the gas molecules themselves are negligible compared with the volume occupied by the gas. (That is, the gas consists of mostly empty space).

Thermal equilibrium – two bodies are said to be in thermal equilibrium if there is no net heat flow between them; that is, they have the same temperature.

Thermometric property - a physical property that varies continuously with temperature.

Triple point of water - the temperature at which all the three states of water co-exist in equilibrium. (273.16 K)

Empirical scale of temperature - one that has been established from experiment. (E.g. the Centigrade scale.)

Centigrade scale of temperature – one that has been established from experiment using the melting point of ice (0 0C) and steam (100 0C) as fixed points with 100 equal divisions between them.

Thermodynamic scale of temperature – an absolute scale of temperature which is based on theory and does not depend on the property of any particular substance. (E.g. the Kelvin scale.)

Specific heat capacity - the quantity of heat required per unit mass of a substance to produce a unit temperature rise.

Heat capacity - the quantity of heat needed to produce unit rise of temperature in the body.

Specific latent heat of fusion - the quantity of heat required to change unit mass of a substance from solid to liquid without a change of temperature.

Specific latent heat of vaporization - the quantity of heat required to change unit mass of a substance from liquid to vapour without a change of temperature.

Internal energy (of a system) - is the sum of the random distribution of kinetic and potential energies associated with the particles that make up the system.

lst Law of thermodynamics - the increase in internal energy of a system is equal to the sum of heat energy supplied to the system, and the work done on the system.