For a dilute solution of known (*) ionic strength, this quantity can be found with the Debye-Huckel limiting law.
This quantity and mole fraction are correlated for a compound in the NRTL model for calculating phase equilibria. Another model for calculating this quantity, which appears on the y-axis of a UNIQUAC diagram, begins by breaking it into combinatorial and residual components. An expression equal to this quantity is obtained by differentiating the virial expansion of the Pitzer equation. For a dilute solution of known (*) ionic strength, this quantity can be found with the Debye-Huckel limiting law. The fugacity coefficient and this quantity may be used to adapt Raoult's law to non-ideal solutions. For 10 points, name this dimensionless correction factor, symbolized gamma, that accounts for a liquid's deviation from an ideal solution. 
This quantity and mole fraction are correlated for a compound in the NRTL model for calculating phase equilibria.
activity coefficient [prompt on "activity"] 