All the fun comes from phase changes - in our example the formation of H 2 O in a somewhat violent fashion. It was thought that the sign of dH would indicate if a reaction should or should not occur. A negative sign would mean that the reaction would transfer energy to the surroundings and thus could easily happen, whereas a positive sign would tell us that energy would have to be pumped into the system - nothing would happen by itself. Before turning to the entropy, a word to the choice of state functions. F - but for a given system, there is only one state.
All molecules are in the left half of the container.
However, the probability of experimentally finding one or the other of those macrostates is very different. The probabilities of the macrostates 1. and 2. are certainly much much smaller than the probability of macrostate No. 3. The corresponding microstates are the possible combinations of the individual dice. An example just as easy as playing dice, comes from our friend, the vacancy. When we figure that out, we can use the equilibrium condition to select the most likely macrostate and this gives us the number of vacancies in equilibrium.