According to constructivism, which is one of the popular learning theories in recent years, students construct their own knowledge based on their personal experiences and interaction with other people. In some cases, this knowledge may not overlap with the scientifically accepted view, resulting in students’ misconceptions. Misconceptions have different sources including textbooks, teachers’ instruction and daily life situations, and they are resistant to change. Therefore, it is important to identify them first and then develop suitable teaching strategies accordingly. Several research studies were carried out about students’ misconceptions of energy in chemical reactions concepts such as heat and temperature, endothermic and exothermic reactions and bond energy (Barker & Millar, 2000; Ben-Zvi, Eylon & Silberstein, 1987; Boo, 1998; BouJaoude, 1991; Ceylan, 2004; De Vos, & Verdonk, 1986; Erickson, 1979). However, enthalpy concept was not explored at high school level in the literature. The purpose of this study was to investigate 10th grade high school students’ conceptions about enthalpy concept. Research question is: What are the 10th grade high school students’ conceptions about enthalpy concept?

Sample In this study, participants were 222 Turkish high school mixed-ability students. This sample consisted of approximately equal number of males and females. The participants were 10th grade students who learnt energy in chemical reactions concept previously. Instruments Two instruments were used in this study in order to collect data. One of them was Energy in Chemical Reactions Concept Test (ECT). The other one was semi-structured interviews. ECT included 20 multiple-choice questions which had five alternatives and designed widely according to misconceptions found in the literature (Baujadeu, 1991; Boo, 1998; Ceylan, 2004; De Vos & Verdonk, 1986; Kesidou & Duit, 1993; Yeo & Zadnik, 2001). Moreover, during the preparation of the ECT some chemistry teachers’ comments were taken about the possible difficulties of energy in chemical reactions concept. And, this test (ECT) was prepared to determine the misconceptions considering subtitles of the energy in chemical reactions concept; heat and temperature, exothermic and endothermic reactions, bond energy, combustion reactions, enthalpy and calorimeter. While some of the questions were adapted from the related literature, some of them developed originally by the researchers. Content validity of ECT was assessed by five chemistry teachers and one chemistry educator. For the reliability of the test, Cronbach alpha value was found 0.70. For this paper, four questions related to enthalpy in ECT were discussed. In order to get deeper information about students’ conceptions about the enthalpy concept, semi-structured interviews were carried out with seven students, who completed ECT. A semi-structured interview schedule was prepared considering students’ responses given to four questions about enthalpy in ECT. Interviewees were selected considering frequencies of students’ responses for each of these questions in the test. Each interview was audio-taped and transcribed. Analysis For the analysis of data, frequencies of students’ responses for each question related to enthalpy concepts in ECT were found by using descriptive statistics. Interview conversations were also used to supplement the results of questions in ECT.

Results and Implications Analysis of data indicated that students had difficulties in understanding the enthalpy concept, specifically enthalpy of formation. The below statements are some misconceptions found in this study: •Enthalpy of formation and ΔH are always the same thing. •Enthalpy of a reaction doesn’t depend on the phases of the reactants and products. •If ΔH is positive (+), amount of products is bigger than that of reactants. On the other hand; enthalpy of combustion was not appeared to be a problematic point. It can be understood from this study that the meaning of enthalpy is not clear enough in Turkish students’ minds. That means; giving the textbook definitions does not work. They just memorize and when they face problems that require thinking critically, they are confused. Instead of knowledge transmission from teacher to students, students should be given the opportunity to construct their knowledge by themselves in order to learn the concept meaningfully.