ABSTRACT
In this chapter, we continue our study of thermodynamics. We expand from Chapter 4 by looking at the second law of thermodynamics and the related concept of entropy. In short, the second law establishes the bounds for what can happen in the real world. To formalize the second law, we expand the review of heat engines and reversible processes initiated in Chapter 4. An important tool to understand thermodynamic cycles is the temperature and entropy (T-s) plane, which we employ to discuss efficiency and the Carnot limit. We further examine the concept of internal energy by including enthalpy and Gibbs free energy. Armed with these concepts we study thermochemical processes, or those that involve chemical change. We end the chapter applying this knowledge to fuel cells, using hydrogen fuel cells as an example. Compared to a heat engine, in a fuel cell conversion goes directly from chemical to electrical energy. As in Chapter 4, further reading is available in fundamentals of thermodynamics textbooks [1,2]. In addition, several textbooks on energy systems [3-5] contain reviews of thermodynamics that can supplement the presentation given here. Thermodynamics have applications to environmental, ecological, and biological systems, which will not be discussed in this book. However, the reader is referred to Jorgensen and Svirezhev [6] and Morowitz [7]. A good source for further reading on the thermochemical section including fuel cells is Masters [8].
