In this study, we calculated the excess molar enthalpy HmE, of acetonitrile mixed with 1,2-dichloroethane, 1,1,1-trichloroethane, 1,1,2,2-tetrachloroethane, trichloroethylene, and tetrachloroethylene using a calorimetric method at a temperature of 303.15 K and a pressure of 81.5 kPa with a Parr/1455 solution calorimeter. We also determined the excess partial molar enthalpies HE m,i, excess partial molar enthalpies at infinite dilution HE,∞ m,i , and the intermolecular interactions function H i−i. The results were analyzed using the Redlich– Kister polynomial relation. Various local composition models, including Wilson, Universal Quasi-Chemical (UNIQUAC), and Non-Random Two-Liquid (NRTL) were investigated. The equation state of Prigogine Flory–Patterson (PFP), was also applied. Notably, acetonitrile showed exothermic behavior when mixed with 1,2-dichloroethane and 1,1,2,2-tetrachloroethane, whereas it exhibited endothermic behavior with 1,1,1-trichloroethane, trichloroethylene, and tetrachloroethylene. Endothermic behavior (positive enthalpies of mixing) signifies that the actual enthalpy of mixing is higher than expected for an ideal solution, indicating repulsive interactions. In contrast, exothermic behavior (negative enthalpies of mixing) denotes that the actual enthalpy of mixing is lower than expected, suggesting attractive interactions.
