Thermal Physics and Temperature

Thermal Physics and Temperature is the second lecture within the Properties of Matter section of PH1011. It covers thermal equilibrium, the laws of thermodynamincs, and ideal gases.

Previous: Properties of Matter

Next: The Kinetic Theory of Gases I

Temperature
The 0th Law of Thermodynamics states that:


 * 1) "If bodies A and B are in thermal equilibrium with C, then A and B are in thermal equilibrium with each other."

Temperature scales are defined using fixed points - eg Celsius uses the freezing and boiling points of water, Kelvin uses absolute zero and the triple point of water (273.16K) - and temperatures between these values can be found through an interpolation. Suplying heat to an object increases its temperature as it increases the kinetic energy of the molecules, making them vibrate faster.

Gaseous relationships
Gas thermometers require fixed volumes to allow the pressue to be measured. This is due to the ideal gas laws -
 * Charles' Law; V α T at constant P
 * Boyles' Law; PV = constant at constant T (also P α (1/V))
 * Gay-Lussac's Law; P α T at constant V

A combination of these gives PV α T or PV/T = constant. However, these only hold true for ideal gases, with these properties:
 * Individual particles have 0 volume
 * No intermolecular forces are apparent
 * All collisions are elastic
 * Particles are in constant random motion

Most gases behave ideally around standard temperatures.

Ideal Gas Equation
Avogadro hypothesised that equal volumes of gas at equal temperatures should contain the same number of molecules regardless of molecular mass ect. This agrees with experimental findings and gives the ideal gas equation - PV = nRT where n is the number of moles and R is the idea gas constant 8.3JK-1m-1.

Summary
Temperature is defined on fixed point scales. The three gas relationships can be combined to give a master constant. Avogadro was an absolute legend.