For a single species in a mixture and all else constant, the partial molar value of this quantity is equivalent to its chemical potential.  
Setting the partial derivative of this quantity equal to zero will allow one to arrive at the standard form Kohler Equation, and at constant temperature, the partial derivative of this quantity with respect to pressure is simply equal to volume.  For a single species in a mixture and all else constant, the partial molar value of this quantity is equivalent to its chemical potential.  Its standard change in a voltaic cell is defined as the negative product of moles of charge, Faraday constant, and potential difference, while in a chemical reaction it is the negative product of the ideal gas constant, temperature, and the equilibrium constant.  Most generally defined as enthalpy minus the product of temperature and entropy, FTP name this thermodynamic parameter whose change must be less than zero for a reaction to be spontaneous.
Setting the partial derivative of this quantity equal to zero will allow one to arrive at the standard form Kohler Equation, and at constant temperature, the partial derivative of this quantity with respect to pressure is simply equal to volume.  
Gibbs Free Energy