Predicting and explaining the evolution of chemical systems Observation of the implementation of a new chemistry curriculum in the final year of higher secondary education, reactions of the teachers and students confronted with the introduction of the evolution of chemical systems.
UFM de Créteil, LDSP Université Paris-Diderot Paris7, France
This work examines the effects of the implementation of a new curriculum on the evolution of chemical systems in the final year of higher secondary education in France. The first part includes an analysis of the curriculum which defines the structure of the subject matter highlighting the underlying models and their links with empirical level and determines in what measure the didactic intentions of the authors are translated into precise contents and skills. The second part sets out the reasoning and difficulties encountered by the students for whom the use of the evolution criterion is not always rational and is often studded with errors. Some errors (modification of the reaction quotient, impossible evolution direction) may be due to the difficulty they have in differentiating between the empirical level and the model level or vice-versa, or in moving between these two levels. The analysis of the explanations provided at the stopping point of the evolution of a system shows that a poor use is made of the evolution criterion and of the macroscopic kinetic model and that there is no allusion to the microscopic kinetic model. The third part deals with the teachers’ professional knowledge through interviews in which they are confronted with students’ authentic responses. The introduction of the evolution criterion is rightly perceived as an issue of this programme contrary to two others themes: the distinction between chemical change (empirical level) and chemical reaction (model level) and the use of the microscopic kinetic model. The presentation of students’ responses to the teachers may reveal their difficulties or develop their professional knowledge if they have the mastery of the subject matter content by giving them the opportunity to identify students’ errors which they were not aware of. The conclusion pinpoints some relevant details to design teaching learning sequences and some precise directions to devise teacher training sessions.
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