Historical Perspective: More than half a century ago, the typical chemical engineering program began with a course devoted to material and energy balances. The dominant text was Chemical Process Principles (1943) by Hougen and Watson. Stoichiometry was covered in four pages and restricted to single independent reactions. More than sixty years later the typical chemical engineering program still begins with a course on material and energy balances. But much has changed in those intervening years. For example, students now have access to powerful computational software (Matlab, Mathematica) and simulators (Aspen). Yet the discussion of stoichiometry in standard undergraduate textbooks is still restricted to mostly single independent reactions, with little if any methodology for handling real world stoichiometry involving multiple independent reactions.
Paradigm Shift: Motivated by the "sketches" of Aris in Introduction to the Analysis of Chemical Reactors (1965), the "foundation" provided by Amundson in Mathematical Methods in Chemical Engineering (1966), and the "perspective" of Reklaitis in Introduction to Material and Energy Balances (1983), we have focused on providing a rigorous treatment of material balances for reacting systems. It is a treatment that will not require revision and upgrading in a subsequent course. Our presentation is based on the two axioms for the mass of multicomponent systems, and it is not limited to single independent reactions. The latter are dominant in the academic world and almost non-existent in the real world where our students must practice their profession. The philosophy behind this text is that the axioms and the associated proved theorems are the tools that we use to solve material balance problems, and are also the basis for the use of computational software to solve more demanding problems. We have purposely avoided any extensive use of software in this text because we believe that having a firm grasp of the theory is what is needed most. There is ample opportunity for students in subsequent courses to focus on numerical solutions of specific problems. In this text we make a clear the distinction between global stoichiometry, local stoichiometry, and the stoichiometry related to elementary reaction steps. It is of no value to the students to shield them from the underlying theory, thus we propose a paradigm shift from the approach initiated by Hougen and Watson to a new and rigorous analysis of chemical engineering fundamentals.
See also: B.G. Higgins & S. Whitaker, Local, Global, and Elementary Stoichiometry, AIChE Journal, 58(2), 538-552, 2012