Heat and Temperature
The Ideal Gas and Kinetic Theory
The Second Law of Thermodynamics and Heat Engines
|Let us take a moment to appreciate the importance of the Kelvin scale, the absolute temperature scale.|
The Kelvin temperature is a central concept to emply in understanding the behavior of an ideal gas at both at the macrostate level and at the particle level. In thermodynamics, the macrostate refers to the point of view of the quantities you measure in the laboratory such as the pressure, volume and temperature. The particle level refers to the point of view of the particles themselves. Often we will be using the macrostate to infer the particle level, and vice-versa.
Because for an ideal gas, the temperature on the Kelvin scale is proportional to the product of the pressure and the volume, the Kelvin scale can be obtained via the macroscopic equation of state for the ideal gas (all gases expand by 1/273 of their volume at 0oC for each degree the are heated above this temperature). Furthermore, because the internal energy of an ideal gas is proportional to its temperature, we can use the Kelvin temperature to reference internal energy changes in the context of the First Law of Thermodynamics.
The Kelvin temperature is also important in the domain of Kinetic Theory, which is the part of thermodynamics in which that is concerned with the view of the gas particles themselves as a statistical distribution. For a sample of ideal gas, viewed at the particle level, the Kelvin temperature describes the kinetic energy of average particle.