A Working Method Approach for Introductory Physical Chemistry Calculations by Brian Murphy, Clair Murphy, and Brian J. Hathaway

Reviewed by Francisco Rey Physical Chemistry Department, Universidade de Vigo, Vigo, Spain frey@uvigo.es

A Working Method Approach for Introductory Physical Chemistry Calculations. The Royal Society of Chemistry. ISBN 0-85404-5534-8. 152 pages.

Many things can be said of this book, but they can be summarized very simply: it is not a physical chemistry book and its usefulness for students is very doubtful. Moreover, it does not meet the minimal objectives one would expect.

It is not a physical chemistry book, even at introductory level, because its contents correspond neither to a traditional syllabus nor to the minimum level for a physical chemistry textbook, even if it is considered just as a supporting text on problem solving. Of the nine chapters, seven are devoted to equilibrium thermodynamics in its different aspects, and only two (which could easily be combined) to chemical kinetics. The book ignores many areas, such as spectroscopy, quantum chemistry, and statistical thermodynamics, and even nonequilibrium electrochemistry. The title is thus pretentious and might well mislead the reader. On the other hand, the depth of analysis is more suited to a general chemistry book.

The authors say that their book is not intended as a "recipe book" from which one can learn to solve problems, but as an introduction to a systematic approach, allowing students to develop their own methods to solve chemical problems. For this, the authors propose a method, requiring that students read the problem properly (not always done!), seek the relevant equations, identify the unknown quantities, and then solve the problem numerically, with the correct units. This method is outlined on page 10 and the remainder of the book is devoted to applying it. I felt that the authors did not really need so many words to explain something so straightforward.

Mathematical problem solving in any branch of science cannot be based on such a strict method, since each problem is different; no method will work for all of them. It is reasonable to think that a systematic approach must exist, but this only can be reached by reasoned resolution of the problems, relying on the specific abilities of each student.

The book contains many mistakes that can trap the novice student, who must then seek help from the teacher. Equally, unnecessary information is presented. For example, there seems little point in defining the oxyacids and oxyanions in Chapter 1, when they occur nowhere else in the text. Examples of this nature are common throughout the (excessive!) pages of the text.

Explanations are perplexing and in many cases, wrong. For example, a clear separation between experimental facts and chemical laws is not made. The volume of any gas decreases with increasing pressure if the temperature is kept constant; this is an experimental fact! By contrast, Boyle's law is only a model, summarizing experiment for an ideal gas. With this formulation, the reader can deduce that the volume of a gas decreases when its pressure is increased. A book whose main objective is to help the student to think cannot be based on affirmations of this sort, even though they occur frequently in other textbooks. On the other hand, the deduction of the ideal gas law is wrong. Such thinking is later applied systematically to more complex topics, where as a result, the reader can lose track of what is being read, rendering the working method valueless.

Those who teach introductory chemistry know that 1) chemical balance is one of the most important topics, in that students can "see" the equilibrium, and 2) the study of equilibria is one area where the students have problems. No general way of understanding equilibria exists and each student will use some personal methodology, invoking basic concepts that are then applied to the particular problem.

It is curious that the book makes no use of partial pressures, preferring to use "concentration" for gases. This perhaps lies behind a serious error that appears in one gas-phase calculation problem. How can anybody with chemistry knowledge assert that when 2 moles of a gas contained in 4 liters are mixed with 2.25 moles of another gas contained in 3 liters, the concentration of the first will be 0.5 M (2/4) and the concentration of the second 0.75 M (2.25/3)? Are the two gases mixed in one container or not? If they are not, the reaction is impossible. If they are mixed, do the gases occupy a different volume? Since this example is 50% of the chapter on chemical equilibrium, the effect on the value of the chapter is obvious.

Errors are apparent in several different sections, but we will mention only a few of the more important. It is asserted on page 53 that a buffer is a solution with an approximately constant pH. However, all stable solutions have a definite and constant pH. Presumably what the authors mean is that the pH of such solutions changes little when small quantities of acids or bases are added - but that is not what they say. A similar confusion in the authors' minds arises in Figure 5.3, where it seems that the pH of a solution is reduced upon addition of a more basic solution. In addition, the authors do not consistently follow IUPAC rules when discussing the concepts of negative catalysis or rate constants. How useful can such a book be when it contains such errors?

Finally, a few mathematical comments. In the resolution of acid and base problems in which quadratic equations appear, it is asserted that these may be solved using an approximation based on the elimination of a variable when its value is likely to be very low compared with other terms (the <5% criteria). In my opinion this is a serious (methodological) error. Using modern calculators, an equation of this type can be solved in seconds. Working with approximate solutions defeats the idea of an equilibrium. Numerical resolution of the problem is less fundamental than the concept itself. A similar criticism can be made of the graphic problems.

In brief, the book fails to reach the minimal level that I would expect. It contains so many errors, and in places is so incoherent, that I will confine it to my file devoted to the worst recent chemistry textbooks (which already holds many textbooks).