It has relatively been difficult to accurately correlateand predictvapor–liquid equilibrium (VLE) data for the strongly associatingsystem containing the carboxyl acid due to its monomer undergoingpartial dimerization and even higher polymerization in the vapor andliquid phases. Herein, this paper reports that the formation statefor the associating component mainly has been the existence of dimerin the vapor and liquid phases through the geometric structures ofethanoic acid investigated theoretically with density functional theory(DFT), and the VLE data for the associating ternary system ethanal+ ethanol + ethanoic acid and the three constituent binary systemswere measured using a recirculating still at 101.325 kPa. Marek’schemical theory was considered due to the associating species as thedimer existence in the both phases. The three experimental binarydata sets were independently correlated using nonrandom two-liquid(NRTL), Wilson, and universal quasichemical activity coefficient (UNIQUAC)model, respectively, and the binary parameters were applied to predictthe VLE data for ternary system without any additional adjustment.By comparison with the measured values, the ternary equilibrium valuespredicted agreed well with the measured values in this way. The thermodynamicconsistency of the experimental VLE data was checked out by meansof the Wisniak’s L–Wtest for the binary systems and the Wisniak–Tamir’smodification of McDermott–Ellis test for the ternary system,respectively. [ABSTRACT FROM AUTHOR]