Kemistudenters föreställningar om entalpi och relaterade begrepp

Sammanfattning: The aim of this thesis was to construct undergraduate chemistry students’ conceptions of enthalpy and its change, internal energy and its change, heat and work. Conceptions make it possible to identify students’ problems with the taught content. How students’ exam results are affected by qualitative/conceptual questions was also investigated.Two chemistry teachers in both secondary school and higher education participated in the first study. Three empirical studies with undergraduate students were done, using a total number of 64, 22 and 10 participants. Methods and tasks from chemistry education research were used and new tasks were developed during the research process. Answers to questionnaires, hand-ins, exams and interview transcripts were analyzed qualitatively. The constructed conceptions were descriptive categories divided into two types, the underlying and the logical.Nine conceptions were constructed. Students expressed enthalpy change as heat at constant pressure like a mantra, since their responses to specific issues contradicted the explicitly used definition. An artifact was necessary to identify work and expansion work and technical work were primarily described as functions of volume. Enthalpy and enthalpy change were considered as a form of energy or as interchangeable.Students argued that enthalpy change and heat were the same, since the reactions were the same, regardless of constant pressure or constant volume. Enthalpy change was heat when no work was done. One possible explanation was that students argued that ΔU was the energy transferred as heat. Students’ interpretations of the tasks clarified that tasks can be further developed. On three of four exams students succeeded better when the qualitative/conceptual questions were excluded. The sample size affected the t-tests and none of the results could be considered significant. Implications for teaching and research are given.