9. Phase Equilibrium
Completion requirements

For phase equilibrium, \(\mu_i^\alpha = \mu_i^\beta\).

Phase Equilibrium Criterion in terms of Fugacity:
Fugacity of component \(i\) in solution is related with composition in terms of two models as already derived in Eqns.(55), and (57). i.e., \[\hat{f_i} = \hat{\phi_i} y_i P\] and \[\hat{f_i} = \gamma_i x_i f_i\] Conventionally the first model is used with gaseous solution, and the second model with liquid solution. And during phase equilibrium, we have \[\hat{f_i}^{\text{v}} = \hat{f_i}^{\text{l}}\] i.e., \[\hat{\phi_i}y_iP = \gamma_ix_if_i \tag*{(59)}\]