Chemical equilibrium and Newton's third law of motion: Ontogeny/phylogeny revisited

Abstract

Evolution of the concept of chemical equilibrium has been strongly influenced by Newtonian mechanics. Even in the late nineteenth century scientists viewed chemical equilibrium as resulting from, an equality of the contending forces, that is, the forward and the reverse reactions. The main purpose of this article is to show that freshman students conceptualize the rates of the forward and reverse reactions in chemical equilibrium as forces, perhaps in the same sense as used in the evolution of the concept of chemical equilibrium and student misconceptions about Newton's third law of motion. Results obtained show that at least some students consider the forward and reverse reactions as a sort of chemical analogue of Newton's third law of motion. Based on this interpretation, it is plausible to hypothesize that student conceptualization of the forward and reverse reactions as forces is ontogenetically (Piaget & Garcia, 1983) a step towards, the deeper understanding of a dynamic chemical equilibrium, leading to a progressive ‘problemshift’ (Lakatos, 1970). In spite of the commonalities between psychogenesis and the history of science, it is important to point out that ontogenesis is not an exact and detailed recapitulation of phylogenesis. Results obtained in this study and their interpretation are important, as they help us to anticipate student utilization of Newton's third law in understanding chemical equilibrium, before the dynamic nature of equilibrium is understood.