Original UNIFAC

<math> ln \gamma_i = ln \gamma_i^C + ln \gamma_i^R</math>

<math> ln \gamma_i^C = 1 - V_i + ln V_i - 5 q_i(1 - \frac{V_i}{F_i} + ln \frac{V_i}{F_i}) </math>

<math> V_i = \frac{r_i}{\sum_j r_j x_j} </math>

<math> F_i = \frac{q_i}{\sum_j q_j x_j} </math>

Molecular volume parameter for component i (k: subgroup index) :

<math> r_i = \sum_k \nu_k^{(i)} R_k </math>

Molecular surface area parameter for component i (k: subgroup index):

<math> q_i = \sum_k \nu_k^{(i)} Q_k </math>

<math> ln \gamma_i^R = \sum_i \nu_k^{(i)} (ln \Gamma_k - ln \Gamma^{(i)}_k ) </math>