text: Generally the chemical potential is given as a sum of an ideal contribution and an excess contribution:
  In an ideal solution, the chemical potential of species i (μ) is dependent on temperature and pressure.
  μ(T, P) is defined as the chemical potential of pure species i. Given this definition, the chemical potential of species i in an ideal solution is
  where R is the gas constant, and  is the mole fraction of species i contained in the solution. The chemical potential becomes negative infinity when , but this does not lead to nonphysical results because  means that species i is not present in the system.
  This equation assumes that  only depends on the mole fraction () contained in the solution. This neglects intermolecular interaction between species i with itself and other species [i–(j≠i)]. This can be corrected for by factoring in the coefficient of activity of species i, defined as γ. This correction yields
  The plots above give a very rough picture of the ideal and non-ideal situation.