A Typology of Undergraduate Textbook Definitions of ‘Heat’ across Science Disciplines

Abstract

The physics and chemistry education literature has grappled with an appropriate definition for the concept of heat for the past four decades. Most of the literature promotes the view that heat is ‘energy in transit’ or ‘involves the transfer of energy’ between the system and surroundings because of a difference in temperature. Given that many undergraduate students are not learning the concept of heat in physics and chemistry alone, the goal of this investigation is to explore the conceptions of heat as presented in textbooks from across the science disciplines. An analysis of the definitions of heat from physics, chemistry, the biological sciences and the earth sciences showed a significant variation in the definitions within a discipline and between the disciplines. Specifically, the physics and chemistry textbooks used ‘energy in transit’ or ‘transfer of energy’ definitions (Class I), whereas textbooks from other disciplines typically used definitions which relate heat to ‘molecular kinetic energy’ (Class II) or they used a hybrid of Class I and II definitions. Although a universal definition of heat across disciplines may not be possible (or even desirable), we suggest that discrepancies in definitions be acknowledged and clearly communicated to students.

Keywords:

• Textbook analysis
• Conceptual development
• Heat

Acknowledgement

The authors thank Marie Molloy for comments on an earlier draft of this paper.

Notes

An example from a physics book is ‘Recall that thermal energy is an internal energy that consists of the kinetic and potential energies associated with the random motion of the atoms, molecules, and other microscopic bodies within an object’ (Halliday et al., 2011, pp. 483–484).

Some authors have cautioned that the words ‘heat flow’ and ‘heat capacity’ imply that heat as a fluid is contained and transferred from one body to the next, with origins from the eighteenth-century caloric theory. Given the nature of physics and chemistry students' learning difficulties, we suggest a greater concern is that such terms reinforce the conception of heat as energy contained in a body.

As has been reported previously (Brookes et al., 2005), the physics textbook authors Serway and Jewett (2008) take a similar approach. They define heat as an ‘energy transfer’ and, throughout the chapter on thermodynamics and end-of-chapter exercises, they use terminology such as ‘energy is added by heat to a system’ (Serway & Jewett, 2008). Furthermore, consistent with de Berg's (2008b) findings, Moore et al. (2011) have taken linguistic care to present end-of-chapter exercises in a manner that is consistent with the process definition of heat (e.g. ‘Calculate the quantity of heating required to convert the water in four ice cubes (60.1 g each) from H₂O(s) at 0°C to H₂O(g) at 100°C’, p. 262), although they do use the phrase ‘heat transfer’ throughout the chapter on calorimetry. Other physics textbook authors who have attempted to present end-of-chapter exercises using phrases consistent with a process-based definition of heat include Cummings et al. (2004), Fishbane et al. (2005), and Halliday et al. (2011).

If ideal behavior is not assumed or if one considers matter in solid or liquid phases, then this conception of heat most closely resembles that component of internal energy which is affected by changes in temperature. ‘Internal energy includes kinetic energy of random translational, rotational, and vibrational motion of molecules; vibrational potential energy associated with forces between atoms in molecules; and electric potential energy associated with forces between molecules. It is useful to relate internal energy to the temperature of an object, but this relationship is limited’ (Serway & Jewett, 2008, p. 554).

Ironically, although Brady and Senese (2009) use a process-based definition of heat, the following passage promotes the conception of heat as kinetic molecular energy:

All forms of energy (potential and kinetic) can be transformed to heat energy. For example, when you “step on the brakes” to stop your car, the kinetic energy of the car is changed to heat energy by friction between the brake shoes and the wheels. (p. 210)