ABSTRACT
In formulation of thermodynamics, we can see how the first law allows us to define the internal energy U which is the sum of the random kinetic and potential energies of the component particles of the system. The second law allowed a definition of the entropy S, and we were able to combine both laws into the central equation of thermodynamics. This chapter explains four extremely useful general thermodynamic relations between the four variables P, V, T and S—the four Maxwell relations. In a purely mechanical system, an idea that the work performed by the system is equal to the decrease in potential energy is familiar. In thermodynamics, however, the situation is complicated by the fact that energy can also be exchanged between the system and the surroundings in the form of heat, and we have to look deeper into the relation between the work performed and the change of energy.
