(e) The Clausius inequality
We now show that the definition of entropy is consistent with the Second Law. To
begin, we recall that more work is done when a change is reversible than when it is
irreversible. That is, |dwrev |≥|dw|. Because dw and dwrev are negative when energy
leaves the system as work, this expression is the same as −dwrev ≥ −dw, and hence
dw − dwrev ≥ 0. Because the internal energy is a state function, its change is the same
for irreversible and reversible paths between the same two states, so we can also write: