Book Review  

Thermodynamics of Chemical Processes by Gareth Price

 Reviewed by
Sonja Krause
Department of Chemistry, Rensselaer Polytechnic Institute, Troy, NY
krauss@mail.rpi.edu
 

Thermodynamics of Chemical Processes by Gareth Price. Oxford University Press (1998), 86 pp.

This short book is no. 56 in the Oxford Chemistry Primers Series. The author's aim is to introduce the concepts needed to treat energy changes during chemical processes and reactions and to explain how these concepts are used to discuss chemical reactivity. The margins, which take up almost one-third of each page, are used to explain mathematical concepts such as integration and differentiation, to show diagrams of apparatus such as a bomb calorimeter, to show schematics such as representation of fluid densities below and above the critical point, and to show tables and graphs. The scope of the book is suggested by the titles of its five chapters:

 1. Preamble: Energy in Chemical Systems

2. Enthalpy and Thermochemistry

3. Entropy in Chemistry

4. Free Energy and Equilibrium

5. Phase Equilibrium and Solutions

This book is meant to be used for a short introductory undergraduate course for students who have taken A-level mathematics in the British system. This is equivalent to a U.S. sophomore course for students who have been exposed to some calculus. Freshmen taking a concurrent calculus course would also be able to use this book. The text is developed in an understandable fashion with many worked example problems and a few additional problems. I would personally be tempted to use this volume as a supplemental text for freshman chemistry. I must admit at this point that I teach at a technical college at which the freshmen have either been exposed to calculus in high school or are taking calculus at the same time as freshman chemistry. Although some calculus is explained in the margins of this book, most students would not be able to learn enough from these margins to understand the text.

The text contains very few mistakes or misprints. One of the few that I could find is the statement that the First Law of Thermodynamics is

U = q + w

for an isolated system, not a closed system. Since the author makes a point of stating that the most common type of system is open, it would also be worth stating that it is very difficult to state the First Law mathematically for an open system, but that this can be done in a number of ways.

This brings me to one of the common oversimplifications made in this book, unfortunately almost standard in explanations of thermodynamics at this level. This is the following statement of the Le Chatelier Principle: "If a system is subjected to a constraint, it will react to minimize the effect of the constraint." This is wrong when stated in this way. As usual, however, the Principle is used correctly in the examples in the text even though the constraints are, again as usual, not stated. For example, when discussing the change in the equilibrium of an exothermic or endothermic reaction when the temperature is changed, the constant pressure constraint should be stated. The Le Chatelier principle should not be stated in the general fashion quoted from this text. It is very specific and should be stated specifically for the types of examples given. It is not difficult to provide specific examples that contradict the general statement. For example, if we assume that the gases involved in the reaction

N₂(g) + 3H₂(g) = 2NH₃(g)

are ideal gases, then, if the mole fraction of the N₂(g) in the undisturbed equilibrium mixture is greater than 0.5, and if the mixture is kept at constant temperature and pressure, then the addition of a small amount of additional N₂(g) will result in a new equilibrium mixture in which even more N₂(g) has been produced. This is a consequence of the second law of thermodynamics; the proper use of the Le Chatelier principle is a consequence of the second law of thermodynamics; it is not an additional thermodynamic law.

Since this otherwise excellent little book errs only in the ways in which most books at this level err, I would recommend it for beginning courses that use calculus. It is much more readable than most books written at a comparable level.