Reactors are equipment in which a chemical reaction takes place. For the chemical engineer, it is an operation of great importance since products that society needs are obtained by chemical transformations of raw materials. It is then fundamental to understand the mathematical models that describe the reacting systems. For a system of sequential reactions the speed law for each participating species is set, obtaining in this way separable differential equations and first order linear differential equations. Undesired reactions that accompany the main reaction can occur in a reactor, so it is relevant to consider all the lateral stages A characteristic example is the antibiotic hydrolysis which can be represented as a series of first order stages in which the desired product is the intermediary [A I P]. Hence, it is necessary that the reactors modelling provides the maximum yield through establishing and solving a differential equation per reaction component. This paper presents the conceptual and procedural learning to obtain the sizing for an intermediary product oxacillin reactor [flucloxacillin oxacillin meticillin], through establishing the differential equations in which the students apply their knowledge in differential and integral calculus, as well as geometrical interpretation of derivatives and integrals. These concepts are necessary to be applied in the interpretation of the point reactor.