First year chemical engineering students' conceptions of energy in solution processes: Phenomenographic categories for common knowledge construction

In this article, we examine first-year chemical engineering students' conceptions of the energy changes taking place in dissolution. Students were individually interviewed with three tasks in which three different salts were dissolved in water, and 17 transcripts were analyzed using a phenomenographic methodology. Four descriptive categories of energy in dissolution were discerned: (a) you give energy (n = 1); (b) water gives energy (n = 17) (c) salt gives off energy (n = 13); and (d) reaction gives off energy (n = 7). Four students gave the same explanation for all three tasks, but more students used the same explanation for two of the tasks: four for Tasks A and B, four for Tasks B and C, and eight for Tasks A and C. Moreover, salt gives off energy was the most common explanation for Tasks A and B (n = 3), reaction gives off energy for Tasks B and C (n = 3), and water gives energy for Tasks A and C (n = 8). Four of the students showed variations of conception within tasks. Students described the solution process of all three tasks using a range of concepts, including previously learned chemical concepts. Even where students used the same chemical concepts in each of the tasks, they did not always give the same meaning to the concepts they used. The phenomenographic categories explanations given by students were used as a basis for developing an approach to teaching energy in solution processes. It is argued that this approach of using phenomenographic categories described at a collective level as a basis for discourse for constructing common knowledge should be used in teaching. It is proposed that a future study must be conducted to develop new trajectories students take to arrive at common knowledge and to understand how to move learners from their personal conceptions to plausible models in solution chemistry within the classroom learning community. Implications for policy are also discussed. (C) 2001 John Wiley & Sons, Inc.