Exothermic Bond Breaking: A Persistent Misconception

Surveys taken the past several years at the onset of an introductory physical chemistry course reveal that the vast majority of students believe that bond breaking is exothermic. This misconception applies, in particular, to the high-energy phosphate bond in ATP, but over 80% of the students also select bond breaking in the reactants as the origin of the exothermic nature of a simple combustion reaction as well. Following a thorough review of the nature of a chemical bond and the overall energy changes in chemical reactions, the students are introduced to the misconceptions that appear in textbooks. In a second questionnaire students are asked for their opinion as to where they have been informed, or misinformed, in their education about bond breaking and bond making. High-school, junior-college, and university biology courses are identified as being primarily responsible, but a sizeable fraction of students feel that they had been misled in chemistry courses as well, particularly at the high-school level. Drawing students' attention early in the course to the confusion surrounding this issue has had the effect of markedly reducing the errors that had always appeared on later exams.