AbstractFor calculations on distillation processes it is necessary to know the vapor‐liquid‐equilibrium (VLE) data at the desired temperature range. Very often data are available only for different temperature ranges. Therefore it is necessary to convert the VLE data from one temperature range to another.—The excess functions of the various types of mixtures have very different temperature dependence. Therefore we classified the mixtures according to the temperature dependence of the excess Gibbs energy and the excess enthalpy. The thermodynamic properties of the mixtures of organic compounds exhibit remarkable regularities.—In the case of non‐associated mixtures the excess Gibbs energy and the excess entropy are directly proportional to the excess enthalpy. Here simple expressions for describing the temperature dependence of the excess functions could be obtainedThe temperature dependence of the excess functions of the associated mixtures can be described by the Chemical Theory of Solutions.—The analysis of the available thermodynamic data shows that our classification serves a two‐fold purpose. First it is very useful for estimating the temperature dependence of excess functions. Second it shows how an analysis of theGEvs.HE(T) curves may enhance the general understanding of interaction