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We present an analysis of the new French curriculum on chemical changes describing the underlying models and highlighting their relations to the empirical level. The authors of the curriculum introduced a distinction between the chemical change of a chemical system and the chemical reactions that account for it. We specify the different roles of the three identified models: a thermodynamic one based on the reaction quotient and the equilibrium constant, a kinetic macroscopic one based on the rates of the opposing reactions, and a kinetic microscopic one. According to our analysis, interpreting the end-point of an incomplete chemical change should offer an opportunity to use the three identified models. We have investigated the reason(s) the students (grade 12) gave to explain why a chemical change remains incomplete, and whether they used one explanatory model more than another. The two macroscopic models were not used by a majority of students, and no student referred to the microscopic kinetic model. A rather high proportion of students held static conceptions of the equilibrium state. These results are discussed.
Kermen et al. (Thu,) studied this question.