Continuous-mixture theory is applied to chromatographic separations based on linear equilibrium partitioning or adsorption of the species in the stationary phase. The mass-balance equation that governs the frequency distribution of a molecular property can be solved exactly when axial dispersion is the sole rate process. This equilibrium-dispersive model also yields expressions for temporal moments, which provide an approximate solution for the distribution. Calculations for examples of the partition coefficient and input distribution yield results that show how separations occur, and how dispersive processes hinder the resolution. Size-exclusion and adsorption chromatography are illustrated. The approach has value for interpreting and explaining chromatographic separations based on molecular properties of mobile complex mixtures that interact with an immobile phase.