The second law is not built into the fundamental laws of nature, though; it arises purely through the laws of probability and the mathematics of very large numbers. But since the probabilities are so overwhelming for any system large enough to see with our eyes, we might as well forget about probabilities and just treat the second law as fundamental.引自第1页Entropy is the more fundamental quantity, governed by the second law of thermodynamics. Temperature is less fundamental; it is merely a characterization of a system's "willingness" to give up energy, that is, of the relationship between its energy and entropy. 引自第1页thermodynamic identity: dU = T*dS - P*dV + ∑ μ*dN. 引自第1页Extensive and Intensive Quantities The number of potentially interesting thermodynamic variables has been growing lately. We now have U, V, iV, S, T, P, /i, H, P, and G, among others. One way to organize all these quantities is to pick out the ones that double if you simply double the amount of stuff, adding the new alongside what you had originally (see Figure 5.9). Under this hypothetical operation, you end up with twice the energy and twice the volume, but not twice the temperature. Those quantities that do double are called extensive quantities. Those quantities that are unchanged when the amount of stuff doubles are called intensive quantities. Here's a list, divided according to this classification:
Extensive: V, N, 5, U, H, P, G, mass
Intensive: T, P, /i, density
If you multiply an extensive quantity by an intensive quantity, you end up with an extensive quantity; for example, volume x density = mass. By the same token, if you divide one extensive quantity by another, you get an intensive quantity. If you multiply two extensive quantities together, you get something that is neither; if you're confronted with such a product in one of your calculations, there's a good chance you did something wrong. 引自第1页Because a system will spontaneously seek out the state of lowest free energy, this property tells us that equilibrium phases almost always contain impurities. 引自第1页The usefulness of the formula F = -k*T* In Z is that from F we can compute the entropy, pressure, and chemical potential, using the partial-derivative formulas 引自第1页Degeneracy pressure is what keeps matter from collapsing under the huge electrostatic forces that try to pull electrons and protons together. Please note that degeneracy pressure has absolutely nothing to do with electrostatic repulsion between the electrons (which we've completely ignored); it arises purely by virtue of the exclusion principle. 引自第1页
