Part IV : Structure, Thermodynamics and Phase Transformations
Module 2 : Regular Solution Model
 

From this expression, one can calculate the free energy of mixing ( $\Delta G^{mix}$), which is the difference between the total free energy and the free energies of (X$_A$ mole of) pure A and (X$_B$ mole of) pure B.

(7)

Thus,

\begin{displaymath} \Delta G^{mix} = \Omega X_A X_B + RT (X_A \ln{X_A} + X_B \ln{X_B}) \end{displaymath} (8)
where $\Omega$ is the regular solution parameter and is given by $N z E_{AB} - \frac{1}{2} (E_AA + E_BB)$. In other words, the regular solution parameter tells us the difference in bond energy when we replace AB bonds by AA and BB bonds.