It gets even easier by restricting ourselves to solids which means that most of the time we don't have to worry about the pressure anymore - it is simply constant. In this primer we will review the most important issues necessary for understanding defects, including defects in semiconductors. We also are sloppy about standards. You are also supposed to know that if Boltzmanns constant k comes up in an equation, we are working with properties per particle, whereas the gas constant R signifies properties per mol. This, admittedly, is dangerous.
Lets stay simple and refer to complications whenever they come up.
If we restrict ourselves to crystals, it is rather easy to consider the concepts behind the all-important thermodynamic quantities Internal Energy , Enthalpy , Entropy , Free Energy and Free Enthalpy . We start with the internal energy U of a crystal. Since at this point we keep the number of atoms in our crystal constant, we only have to consider Q and W if we change the state. Of course, not much happens if the substance stays essentially the same - lets say a mixture of H 2 and O at two different temperatures. All the fun comes from phase changes - in our example the formation of H 2 O in a somewhat violent fashion.