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In undergraduate chemical thermodynamics teachers often include equations and viewmanipulations of variables as understanding. Undergraduate students are often not able todescribe the meaning of these equations. In chemistry, enthalpy and its change are introduced todescribe some features of chemical reactions. In the process of measuring heat at constantpressure, work is often disregarded. Therefore, we investigated how undergraduate studentsdescribe expansion work and technical work in relation to enthalpy and its change. Threeempirical studies (ntot = 64, ntot = 22, ntot = 10) with undergraduate chemistry students takingtheir first or fifth chemistry course at two Swedish universities were conducted. Questions onenthalpy and its change, internal energy and its change, heat and work were administered inquestionnaires, exam questions, hand-ins and interviews. An analytical matrix was developed andqualitative categories with respect to pressure and volume were formed. The results indicate thatwork in general and even more so expansion work and technical work are difficult processes todescribe and relate to the definition and formula of enthalpy change. Work is mainly describedwithout reference to pressure and volume. The properties of volume are more likely to bedescribed correctly than the properties of pressure. The definition of enthalpy change at constantpressure is generalised to constant volume/varying pressure cases. This study gives further insightinto the way in which students use pressure and volume as they describe expansion work andtechnical work as well as the contextual correctness of these descriptions. The matrix andcategories can be used by researchers, teachers and students

An analytical tool to determine undergraduate students' use of volume and pressure when describing expansion work and technical work