13. How To Measure Disorder   Previous PageNext Page

D. Entropy rises with increasing mass, other things being equal. We can show this by comparing the entropies of the diatomic halogens, in order of increasing mass,

or by looking at a series of molecules with increasing numbers of atoms.

This is an important principle, but a hard one to account for without quantum mechanics. Simple quantum theory tells us that as the size and mass of an atom or molecule increase, the spacings between its energy levels decrease. We have used this principle constantly in discussing delocalized electrons in molecules. A large and massive object with a certain total energy has more quantum states available to it, so W is larger and S = k In W is greater. For the nonquantum mechanically inclined, a bull in a china shop creates more disorder than a mouse.







  Page 20 of 45 HomeGlossary