What is the difference between equilibrium stage and rate-based models for mass transfer equipment?

Equilibrium stage models assume vapor and liquid leaving each stage are in equilibrium, using efficiency factors to account for non-ideality. Rate-based (non-equilibrium) models calculate actual mass and heat transfer rates using correlations for mass transfer coefficients, interfacial area, and rigorous multicomponent diffusion (Maxwell-Stefan equations). Rate-based models are essential for reactive distillation, absorption with slow reactions, systems with significant resistance in both phases, and packed columns where efficiency varies with position.