JohnDenker
commented
9 years ago On page 560 the same sort of problem affects the entropy formulas, 20.57 and implicitly 20.58.
Perhaps there is an underlying assumption that all phase changes are isothermal. That is not a good assumption.
A set of hidden (but consistent) assumptions would be bad enough, but here it appears the hidden assumptions are not consistent:
- Defining L in terms of energy (not enthalpy) suggests constant-volume conditions; see #148.
- Assuming boiling is isothermal suggests constant-pressure conditions.
In the box on page 541, associated with section 20.3 and/or 20.4, it defines L = Q/m.
That's a non-starter. This should be obvious from the fact that L and m are properties of the material, whereas Q is not. Q is a functional of the path.
I can think of lots of ways of converting a solid into a gas that involve no Q whatsoever.