Specific methods for predicting liquid-phase excess enthalpy and excess entropy have been developed. These methods consistently use the ASOG group contribution concept for calculating liquid-phase excess properties. The background of the ASOG-based models and their predictive capabilities are demonstrated. A detailed procedure for the calculation of mixture enthalpy and entropy of nonideal systems is given. It allows one to estimate changes in enthalpy and entropy that are necessary for the analysis of chemical processes by the second law of thermodynamics.