Laws of Thermodynamics

We have now come to the end of our investigation of the fundamental postulates of classical and statistical thermodynamics. The remainder of this course is devoted to the application of the ideas that we have just discussed to various situations of interest in physics. Before we proceed, however, it is useful to summarize the results of our investigations. Our summary takes the form of a number of general statements regarding macroscopic variables that are usually referred to as the laws of thermodynamics:

Zeroth Law: If two systems are separately in thermal equilibrium with a third system then they must be in thermal equilibrium with one another. (See Section. 5.3.)

First Law: The change in internal energy of a system in going from one macrostate to another is the difference between the net heat absorbed by the system from its surroundings, and the net work done by the system on its surroundings. (See Section 4.1.)

Second Law: The entropy of an isolated system can never spontaneously decrease. (See Section 5.6.)

Third Law: In the limit as the absolute temperature tends to zero, the entropy also tends to zero. (See Section 5.9.)