Chemical potential at equlibrium

[LalithP]

What is the value of chemical potential of a substance at equilibrium?
According to following article it is zero:

https://www.uni-muenster.de/Physik....hen/Forschungsschwerpunkte/mBECwatfratcp.html

But I have seen in many articles that it is the change in chemical potential (ie. stoichimetric sum of chemical potentials) is zero, not individual chemical potentials. Could somebody clarify this?

 

[Chestermiller]

What is your understanding of the mathematical definition of "chemical potential?"

 

[LalithP]

I think I know the basics like, it is the derivative of internal energy at constant entropy and volume or the partial derivative Helmholtz free energy at constant temperature and volume...

 

[Chestermiller]

The most useful version is the partial derivative of the gibbs free energy G with respect to the number of moles of a given species at constant temperature and pressure. This is the form most extensively used in chemical thermodynamics. The equilibrium criterion for a chemical reacting mixture is that the gibbs free energy is minimized.