Resumen de Macroscopic Observations of Dissolving, Insolubility, and Precipitation: General Chemistry and Physical Chemistry Students’ Ideas about Entropy Changes and Spontaneity
Timothy N. Abell, Stacey Lowery Bretz
Learning thermodynamics requires understanding abstract topics such as entropy and spontaneity. Students tend to rely on metaphors and everyday meanings to reason about these topics. This study investigates how students explain dissolution and precipitation using the concepts of entropy and spontaneity. Students from general chemistry, physical chemistry, and biophysical chemistry participated in semistructured interviews. During these interviews, students observed four tasks: an exothermic dissolving process, an endothermic dissolving process, the insolubility of an ionic salt, and a precipitation reaction. Students reasoned about their observations of dissolving, insolubility, and precipitation by describing entropy as the disorder of a chemical system and describing disorder in several different ways. Few students mentioned microstates or the distribution of energy. Students determined which of the four tasks were spontaneous and offered explanations that included reasoning about changes in enthalpy, reasoning about changes in entropy, and/or using concepts from kinetics. Students’ ideas about entropy changes and spontaneity are examined, and the implications for classroom teaching and future research are discussed.
