Select a reference state, and then adjust the difference between reference and real system. Gas – Ideal gas Liquid – NO single suitable choice: -Lewis / Randal -Henry’s Law Ideal solution -Macromolecular.- when all mixing rules are the same as ideal gas
All molecular interactions are the same! Molecular.- intermolecular potentials are the same between all components in the mixtures
Activity Coefficient = 1 Fugacity of the liquid phase