Molar Heat Capacity for Graphical Pedagogy Applied to Heat Engines, Refrigerators, and Heat Pumps Driven by Chemical Change

Instruction of thermodynamics often begins with a Carnot cycle for the pressure-volume changes of an ideal gas, yet this mechanical treatment can seem far from the minds of biologically and chemically oriented students used to liquids and solids. Herein, as an alternative, a pedagogic narrative of an experimenter, an analyst, and an innovator, all three developed around condensed-phase transitions, is used. Graphs employ heat capacity for an intuitive and visual pedagogy of enthalpy and entropy in chemical thermodynamics. Heat capacity is applied to determine the efficiencies of different types of cyclic machines for phase transitions between generalized phases <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>A</mml:mi></mml:math> and <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>B</mml:mi></mml:math> at high and low temperatures. The exposition thus develops the heat engine, the refrigerator, and the heat pump based on thermochemical cycling. This approach stands in contrast to development based on mechanical cycling. This alternative approach offers deep engagement with thermodynamics for students of bio/chemical disciplines in ways congruent with straightforward laboratory observations. Through visual plots, the approach emphasizes the preeminent and consistent role of heat capacity as the unifying concept among enthalpy, entropy, and phase change.