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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.)

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Richard Fitzpatrick
2016-01-25