Determination of optimal operating conditions of chemical processes is difficult. Minimization of entropy generation is a simpler option for standard, either numerical or analytical, optimization techniques. This paper illustrates how entropy generation minimization can simplify the analysis and optimization of the operation of a CSTR. A typical irreversible, exothermic, first order chemical reaction taken from the literature has been considered. For this system, the entropy generation rate has been derived based on mass, energy and entropy balances. Using analytical derivatives it was found that entropy generation can be minimized if the inlet stream temperature is the same as the operating temperature of the reactor. Additionally, it was easy to draw from the analysis the operating temperature that achieved maximum conversion. Finally, the procedure proposed was compared with an indirect entropy minimization method, and shown to be simpler and clearer.