Modelling Students’ Progression in Chemical Reactions

Abstract

This paper proposes model-based notion of ‘submicro representations of chemical reactions’. We suggest that there are two major models of reactions in school chemistry: (a) Simple rearrangement model. Reactions are simple rearrangements of particles, where particles are the most basic units of rearrangement and do not change their identity in the reactions, and (b) Interaction model. Reactions involve the interactions of different chemical species with – depending on the type of reaction – the participation of electrons and protons. Chemical species change their identities/structures in reactions, e.g., atoms become ions. We conjectured that (i) students in general may demonstrate progression from the Simple rearrangement model to the Interaction model in their learning; (ii) Although the Simple rearrangement model may look less sophisticated, it offers simple explanations to some advanced concepts in kinetics (e.g., simple collision theory) and energetics (bond breaking and formation). Therefore, this model cannot be simply regarded as a weaker model. We interrogated these two conjectures by two interview studies in which we collected data from different schools and grade levels: (1) We analysed how 18 Grade 10-11 students mentally visualized the reaction between magnesium and hydrochloric acid. Each student was interviewed twice – once after they were taught reactions of acids and once after they learned about redox. There was a developmental trend among the students, who progressed from the Simple rearrangement model to the Interaction model. None of the students regressed. (2) We analysed 18 Years 10-12 students’ mental visual representations of the reaction of magnesium and oxygen. We found that a Grade 12 student who represented the reaction based on the Simple rearrangement model explained the reaction in terms of some energetics and kinetics concepts. These studies highlights the potentials of these two models in helping students to develop understanding of chemical reactions.