Teaching and learning of the concept of chemical equilibrium.

Educational research in chemistry has identified the most common learning difficulties and alternative conceptions concerning the concept of chemical equilibrium. These studies show that students have difficulty in predicting the evolution of a system from an initial state or from an equilibrium state, or also that students believe that the forward and reverse reactions alternate and exist as distinctly separate events when equilibrium is attained, or even believe chemical equilibrium as a static state [1]. These students misunderstandings and learning difficulties require the design and testing of educational sequences that allow for meaningful learning of the concept of dynamic chemical equilibrium. Many authors report that a concept is learned significantly when the teaching takes into account of the questions that scientists have set themselves during their research. In such a way issues, contexts of meaning and empirical referents on which the concept of dynamic equilibrium is structured, can be clarified [2]. Moreover, education should be thought of as producing change in a student's conceptions rather than simply accumulating new information within the student's memory [3]. The design of the teaching sequence, which is the subject of this communication, started from the historical and epistemological evolution of the concept of dynamic chemical equilibrium, by taking into account the alternative conceptions and learning difficulties of the students and with the aim to put both the student and the topic to learn within the process of learning and hence to focus on the the dialectical relationship between "the logic of scientific knowledge" and "logic of the student” [4]. The teaching sequence, which was divided into six sections (1. Incomplete chemical transformations, 2. Reverse chemical transformations, 3. Systems in dynamic chemical equilibrium, 4. Evolution of systems I: from a state of non-equilibrium to a state of equilibrium, 5. The equilibrium constant, 6. Evolution of systems II: from a state of equilibrium to another equilibrium state), is based on theoretical questions and practical problems that should allow students to compare and contrast each other ideas and to learn in an active way the concept of dynamic chemical equilibrium. The teaching sequence has been successfully tested in a fourth class of Liceo Scientifico Tecnologico (progetto Brocca) during the school year 2010/2011