Like the grand potential, two of this thermodynamic quantity's natural variables are intensive quantities. This quantity can 
Like the grand potential, two of this thermodynamic quantity's natural variables are intensive quantities. This quantity can be obtained by performing two Legendre ["luh-JOHN-druh"] transforms on internal energy. For an electrochemical cell, the change in this quantity is equal to "minus the number of electrons transferred, times cell potential, times Faraday's constant". It applies to processes which occur at constant temperature and pressure, unlike a quantity named for Helmholtz. This quantity is equal to "enthalpy minus temperature times entropy", and it is negative for spontaneous processes. For 10 points, name this quantity that measures the amount of useable work available in a system.