In the literature of chemical reaction engineering, the basic models for reactors are deduced in different ways, This paper demonstrates that the authors do not always stringently differentiate between fluid mechanics and chemical reaction engineering methods. Thus misinterpretations may arise. As this publication shows, it would be more precise to use instead of ideal reactors the term completely/radially mixed reactors (mixing vessel/pipe). In addition, attention is directed to convection reaction models. They give an idea of the local concentration profiles in reactors for a small mathematical effort. The models give predictions superior to those of the ideal reactor models and of the dispersion model, both of which can only give mean values.