This paper proposes a model-based notion of "submicro representations of chemical reactions". Based on three structural models of matter (the simple particle model, the atomic model and the free electron model of metals), we suggest there are two major models of reaction in school chemistry curricula: (a) reactions that 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) reactions involving the interactions of chemical species with--depending on the type of reaction-- electrons and protons. In the latter case, chemical species change their identities/structures in reactions; for example, atoms become ions. Based on these two models, we analysed how 18 Grade 10-11 students mentally visualised the reaction between magnesium and hydrochloric acid. Each student was interviewed twice--once after they were taught the reactions of acids and once after they learned about redox. Their visualisations could be fitted into these two models. There was a developmental trend among the students, who progressed from the simple model to the more sophisticated model. None of the students regressed. Curriculum planning and teaching should consider how students should be helped to learn about different reaction models.