Читать книгу Geochemistry - William M. White - Страница 45

Our discussion of entropy might leave the impression that entropy is associated only with heat and temperature. This is certainly not the case. Our first example, that of the gases in the box (Figure 2.5), is a good demonstration of how entropy changes can also accompany isothermal processes. When the partition is removed and the gases mix, there is an increase in the number of states accessible to the system. Before the partition is removed, there is only one state accessible to the system (here, accessible states means distribution of red and black molecules between the two sides of the box), so Ω = 1. Suppose that after we remove the partition, we find the system state is one where there is one molecule of each kind on each side (the most probable case). There are four such possible configurations, so Ω = 4. The entropy change has thus been

From the macroscopic perspective, we could say that the red gas, initially confined to the left volume, expands into the volume of the entire box, and the black gas expands from the right half to the entire volume. Thus entropy changes accompany volume changes.