# Stoichiometry with out tears

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Chemical Engineering Education, 24(4), 188–196 (Fall 1990).

CHE curriculum

STOICHIOMETRY WITHOUT TEARS
RICHARD M. FELDER
North Carolina State University Raleigh, NC 27695

Students who are about to take stoichiometry fear it, and many who are currently taking it hate it. The homework never ends, and you can spend hours on a single problem without getting anywhere. It’s the weedoutcourse—30%, or 50%, or 70% flunk it, depending on the institution, the class size, and who is teaching. So what’s in this killer stoichiometry course? “What goes in either comes out or stays in,” that’s what—and usually we never get to the part where it stays in, leaving us with Input = Output. Not exactly intellect-stretching stuff. Of course, there’s more— gas laws (PV = nRT: given three variablevalues, solve for the fourth), simple vapor-liquid equilibrium relations [yAP = pA*(T): given a vapor pressure correlation and two of the variables yA, P, and T, solve for the third variable], and energy balances (Q =∆H: given feed and outlet conditions, calculate ∆H by integrating heat capacities and adding latent heats, and then solve for Q). That’s about it. The energy balances give the studentstheir first brief immersion in the alphabet soup of thermodynamics, but only up to U and H—and most of those who go down in the course are lost well before they get there. What defeats many of them, I believe, is the simplicity of the subject matter. The course starts off with deceptively easy material: units and dimensions, definitions of process variables, and material balance problems that canbe solved with college freshman and even high school methods. We
Richard M. Felder is professor of ChE at N.C. State, where he has been since 1969. He received his BChE at City College of New York and his PhD from Princeton. He has worked at the AERE, Harwell, and Brookhaven National Laboratory, and has presented courses on chemical engineering principles, reactor design, process optimization, andradioisotope applications to various American and foreign industries and institutions. He is coauthor of the text Elementary Principles of Chemical Processes (Wiley,1986).