MOLECULAR-EQUILIBRIUM PROBLEMS - MANIPULATION OF LOGICAL STRUCTURE AND OF M-DEMAND, AND THEIR EFFECT ON STUDENT PERFORMANCE

Molecular-equilibrium (chemical-equilibrium) problems are among the mo st important, and at the same time most complex and difficult general chemistry problems. In this work, we examine the effect on student per formance of the manipulation of the logical structure as well as of th e M-demand of these problems. In addition, we study the relationship b etween student performance on the problems and a number of cognitive v ariables, viz., developmental level, working memory capacity, function al M-capacity and disembedding ability of students. In addition, we te st the validity of the Johnstone-El-Banna model. Nine problems of vary ing number of operative schemata, as well as of varying number of M-de mand, were used. The number of schemata varied froth a-minimum of two, to a maximum of four, while within each logical schema we had specifi c mental demand (M-demand), varying from four to six. As basic molecul ar-equilibrium schemata in these problems, we considered the following : (1) the process of establishment of chemical equilibrium; (2) the co ndition of chemical equilibrium; (3) the case of gaseous systems, with use of partial and total pressures as well as of K-p; and (4) the dis turbance of equilibrium and the establishment of a new equilibrium. Th e correlation between student performance in the schemata and the step s of the problem solutions is low when the number of schemata is low, but high when this number is high. Of the cognitive factors studied, d evelopmental level plays the most important role, especially as the lo gical structure of the problem increases. The other three cognitive va riables also have an effect, with working memory capacity leading. The findings are mainly attributed to the fact that the problems were rat her algorithmic exercises for the students, because of familiarity and training. (C) 1998 John Wiley & Sons, Inc.