| . . .This is the origin of one of the lines
| of confusion in thermodynamics. The definition dS = dQrev/T gives the
| impression that, at least for an ideal gas, the entropy is a state
function
| only if the system undergoes a reversible process. On the other hand,
the
| nature of the ideal gas as reflected by eq. /1/ guarantees that the
entropy,
| if defined by dS = dQ/T, will also be a state function provided the
system is
| in equilibrium all along. . . . From: "Pentcho Valev" <pvalev@BAS.BG>
Pentcho,
I think this passage points out the heart of your confusion. Even though
S (along with other state variables) is a state function, this does not
preclude the system undergoing processes in which the state is not even
defined, because the system is in dis-equilibrium. "S is a state
function" means that whenever the system is in a defined, equilibrium
state, the value of S is determined by that state. Your statements: "
...the entropy is a state function only if the system undergoes a
reversible process" and later ". . .will also be a state function
provided the system is in equilibrium all along" have no useful meaning.