I am trying to understand the implications of the principle that the maximum non-expansion work, dwadd is equal to the Gibbs energy change for a reversible process.
For a reversible process, dwadd = dG.
This is provided that the process takes place at constant pressure and temperature.
The Attempt at a Solution
The source of my confusion is to do with the fact that if the Gibbs energy change of a system, dG, is zero at constant temperature and pressure, then that system is at equilibrium. When a system undergoes a reversible change, it passes through a series of equilibrium states before attaining its final state. Hence, for a reversible process,
dG = 0
But, dG = dw add
So that seems to imply that for any reversible process, the non-expansion work available is always zero, which doesn't seem to be true.
Would greatly appreciate any clarifications. Thanks in advance.