In the last chapter of this textbook, which is also the second chapter devoted to non-ideal reactors, we will focus on the design equations in presence of a chemical reaction. The concepts of maximum segregation and maximum mixing reactor will be presented, developing the related characterising equations. Using the point of view that these two models represent the extremes of any non-ideal configuration with a given distribution of residence times, the expected conversion degree will be discussed. Subsequently, in the hypothesis of a tubular reactor with slight deviations from the ideality of the plug flow, the axial dispersion reactor will be presented and, finally, the case of fluid dynamics opposite to that of the plug flow (i.e., tubular reactor with laminar flow) will be discussed, with the consequent design equations.