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Enhancing Understanding of Equilibrium Concepts in General Chemistry using the Systematic Method

Abstract

This study investigates an alternative to the commonly used concentration table method for describing chemical equilibria in General Chemistry. The concentration table method is arguably the single most difficult concept for students in this course. The difficulties arise from the number of simplifying assumptions that need to be made. Furthermore, once the problem has been simplified, a significant amount of time is often required for algebraic manipulations, which students in General Chemistry find difficult. As discussed in this paper, it is possible to deal with equilibrium in a more contemporary, holistic approach, where equilibrium expressions, charge, and mass balance equations are solved simultaneously. Such methods reduce the number of assumptions that need to be made to solve a given problem, and when solved using a symbolic computer algebra program, provide a reduction in the amount of work required to reach a numerical solution. Also, since multiple equilibrium reactions are no more difficult to solve than single reactions, students gain a more complete understanding of chemical equilibrium systems. In this study, we present preliminary results from a pilot study in which several different sections in our General Chemistry course are taught using the systematic method. Student understanding of key chemical concepts is monitored and compared to sections which are taught in the traditional manner. Student attitudes are also assessed in terms of perceived difficulties in learning the new method as well as student comfort with working with technology to solve problems. At present, we can state that no significant degradation in student scores is observed. Students in the test sections seem to be performing the same as or slightly above their peers in the standard sections.

Introduction

General chemistry is an important foundational course for engineering studies. This is particularly true for chemical, environmental, and mechanical engineering, but all disciplines rely on general chemistry to varying degrees. Certainly, all four-year engineering programs begin with general chemistry in the freshman year. An important area of study within general chemistry focuses on the concept of chemical equilibrium. Weak aqueous acids and bases, precipitation equilibria, and gas-phase equilibria are standard topics. Students are taught to calculate equilibrium concentrations given total concentrations and equilibrium constants for the relevant reactions.

For determining equilibrium concentrations in reacting systems, the method that is currently taught is to write a concentration table to describe the reaction, and then solve for the unknown concentrations in the table by substitution into the equilibrium expression. This method is demonstrated below for a weak monoprotic acid, written

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Kalainoff, M. Z., & Riegner, D. E., & Deloia, M., & Lachance, R., & Biaglow, A. (2006, June), Enhancing Understanding Of Equilibrium Concepts In General Chemistry Using The Systematic Method Paper presented at 2006 Annual Conference & Exposition, Chicago, Illinois. 10.18260/1-2--1290