Distillation and absorption are well-known separation processes that quite often can be designed using the concept of theoretical stages. The distillation of wide boiling systems, as well as absorption accompanied by chemical reactions, are processes in which this concept typically fails. A nonequilibrium model is presented, which takes into account heat and mass transfer including chemical reactions. In the first part of this publication, the capability of the model to describe the heat transfer is discussed. The model is compared with analytical solutions for the heat transfer and experimental data of heat transfer in columns for both aqueous and nonaqueous systems. Furthermore, the predictions of this rigorous model are compared with analytical solutions for well-known problems of absorption accompanied by chemical reaction. The impact of different numbers of film segments and different grid distributions is especially investigated. Furthermore, a method for choosing a meaningful grid distribution to obtain accurate results with a low number of film segments is proposed, which helps to reduce the computational effort of these calculations.