Absolute activity of a constituent

The canonical partition function relative to corrstituent A is a priori a function of / (or 7), of voltrme and amount Aa of the constituent. We can therefore write the differential of this partition function m the form  

Everything happens as if, in the fust term of equation [5.19], term is a constant and therefore by differentiating this expression with this condition, it 

Remembering that the chemical potential is given by relation [5.48], we find that we can write  

This relation is tme regardless of the statistic used, whether Maxwell-Boltzmarm, Bose-Eirrstein or Fermi-Dirac statistics. 

- The chemical potential here is the generalized chemical potential which, for example, for the electrically charged particles, is the electrochemical potential.  

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