The unit introduces basic concepts that are essential for the control of processes involved in various industries related to chemical engineering and materials science. The theoretical aspects of homogeneous and heterogeneous reactions are studied, as well as the main types of interactions occurring in solutions – van der Waals, solvation processes, hydrogen bond formation. The mechanisms of macroscopic phenomena such as phase separation (when water does not mix with oil) and phase transition (melting, crystallization, etc.) are explained, in relation with intermolecular interactions. The lab practice reinforce the acquired theoretical knowledge. One of the practical classes shows how intermolecular interactions and environmental conditions (such as temperature, for example) affect the solubility of a given substance. For instance, water and xylene do not mix well, but by adding acetone we can improve the solubility of xylene in water. Above the so-called binodal curve presented in the figure, we observe a homogeneous solution, and below it – separation of a layer of xylene.