The model is a choice, and it matters
K-values (how each component splits between vapor and liquid) come from a thermodynamic property method, and the wrong choice gives confidently wrong answers.
Ideal (Raoult) — fine for similar, non-polar molecules at low pressure (benzene/toluene).
Peng–Robinson / SRK (cubic equations of state) — light gases and hydrocarbons, high pressure.
NRTL (activity coefficients) — strongly non-ideal polar mixtures: alcohols with water, anything that forms an azeotrope.
Ideal for easy mixtures, an EOS for gases/pressure, NRTL for polar/azeotropic systems.