The course starts with an introduction to ideal- (or model-) reactors (batch reactor, ideally mixed and plugflow reactor) and their characteristics. Setting up and solving the correct mass and energy balances plays a major role in the dimensioning of chemical reactors and is therefore a basic element of this course. With these balances, the degree of conversion, selectivity and yield for single and multiple reactions in single phase systems are calculated for stationary and instationary operation, for cascades of these modelreactors and for reaction systems of constant- and changing density. Subsequently the concept of Residence Time Distribution is introduced and used to describe non-ideal, intermediate states of mixing for continuous operated reactors, using both the tanks-in-series model and the plugflow-with-axial-dispersion model. The effects of micromixing (in addition to the macroscopic state of mixing discussed above) is discussed. The section on single phase reaction systems (and reactors) is concluded by analysing and solving problems related to combined heat effects with chemical reaction systems, especially in view of stable- and unstable operating points.