the limiting reactant has reacted, the two definitions contradict each other. Combining those two also means that stoichiometry needs to be taken into account and that yield has to be based on the limiting reactant (k in 1..n): Continuous The version normally found in the literature: Selectivity Instantaneous selectivity is the production rate of one component per production rate of another component. For overall selectivity the same problem of the conflicting definitions exists. Generally, it is defined as the number of moles of desired product per the number of moles of undesired product (Definition 1). However, the definitions of the total amount of reactant to form a product per total amount of reactant consumed is used (Definition 2) as well as the total amount of desired product formed per total amount of limiting reactant consumed (Definition 3). This last definition is the same as definition 1 for yield. Batch or Semi-Batch The version normally found in the literature: Continuous The version normally found in the literature: Combination For batch and continuous reactors (semi-batch needs to be checked more carefully) and the definitions marked as the ones generally found in the literature, the three concepts can be combined: For a process with the only reaction A -> B this mean that S=1 and Y=X. Abstract Example For the following abstract example and the amounts depicted on the right, the following calculation can be performed with the above definitions, either in batch or a continuous reactor. A -> B A -> C B is the desired product. There are 100 mol of A at the beginning or at the entry to the continuous reactor and 10 mol A, 72 mol B and 18 mol C at the end of the reaction or the exit of the continuous reactor. The three properties are found to be: The property holds. In this reaction, 90% of substance A is converted (consumed), but only 80% of the 90% is converted to the desired substance B and 20% to undesired by-products C. So, conversion of A is 90%, selectivity for B 80% and yield of substance B 72%. Literature Werner Kullbach: Mengenberechnungen in der Chemie. Verlag Chemie, Weinheim 1980, . Eberhard Aust, Burkhard Bittner: Stöchiometrie - Chemisches Rechnen, CICERO-Verlag, Pegnitz, 4. Auflage, 2011, . Uwe Hillebrand: Stöchiometrie, Eine Einführung in die Grundlagen mit Beispielen und Übungsaufgaben, 2. Aufl., Springer-Verlag, Berlin Heidelberg 2009, . References Stoichiometry