Introduction

Physical chemistry is concerned with the structures of chemical compounds, the mechanisms by which these compounds react and the energy changes that accompany the reactions between the chemical species. Studies in these fundamental aspects of the subject are based largely upon experimental measurements, but theoretical and computer-simulation techniques provide powerful additional methods of investigation. Notwithstanding the subject has, for convenience here, been subdivided, the sections are inevitably linked, so that the order in which they are treated is simply a matter of preference.

All chapters are provided with sets of problems, for which detailed solutions are available on the Internet (see Preface), that have been designed to enhance the reader's appreciation of the subject matter. The reader is encouraged to attempt these problems, and the material described in Appendix 1 should be of assistance in this aspect of the study.

Structure

The term structure embraces a wide range of properties, among which we may include the stereochemistry of a molecule, the lengths of bonds between its atoms, the angles between pairs of bonds, the vibrations of atoms and groups of atoms, the distribution of electron density, the arrangement of molecules in the condensed state and the contact, or nonbonded, distances between species.

In the water molecule H2O, for example, each hydrogen atom is linked to the oxygen atom by a bond that is mainly covalent, with O–H bond lengths of 0.096 nm and an H–O–H bond angle of 104.4˚; the distance between the two hydrogen atoms, the intramolecular proton separation, is 0.152 nm.

An important part of the study of physical chemistry is problem-solving. This activity may range from the evaluation of a parameter from a given equation to the detailed interpretation of a set of experimental data. An involvement with numerical work conveys an understanding of the magnitudes of physical quantities. This facility is important, because computers and hand calculators produce sensible results only if they are supplied correctly with good data.

Solving numerical problems

Numerical problems give practice in relating experimental observations to theoretical models. The insertion of magnitudes into a given equation is a common scientific activity that should be mastered.

The solving of problems leads to an appreciation of several important features:

1. (a) the orders of magnitude of physico-chemical quantities;

2. (b) the need for an understanding of units;

3. (c) the value of checking dimensional homogeneity;

4. (d) the sources of physico-chemical data;

5. (e) the precision of the data and its transmission to the result.

Most problems involve algebraic manipulation. However, it is essential to obtain a clear picture of the physical chemistry involved in a problem before embarking on a series of mathematical processes, and it is useful to obtain an explicit algebraic expression before inserting numerical values. There are several advantages in so doing:

1. (f) the expression can be checked dimensionally;

2. (g) the possible cancellation of terms would simplify the arithmetic;

3. (h) similar problems with other magnitudes can be solved with little additional effort;

4. (i) it is good examination practice.

This book is a complete revision of an earlier work of the same title by the author and his late colleague, Dr W H Lee. It is intended to meet the requirements of students in their first and second years of a degree course in chemistry, or in those sciences for which chemistry forms a significant part, and so to prepare the ground for more advanced final-year studies in this subject.

The mathematical arguments that have been employed in the book should lie within the scope of any chemistry degree student, who will have studied mathematics to A-level, or its equivalent, at least. Physical chemistry is not a nonmathematical subject: any attempt to make it appear so will probably detract from the elegance that attends those approaches that have served this subject well. Some less familiar mathematical topics are discussed in appendices.

Each chapter has been provided with a set of problems designed to enhance the reader's appreciation of the subject matter and its application to new situations. A suggested scheme for solving problems has been given in Appendix 1. The ready availability of computers means that much more extensive data sets can be handled than would be reasonable with hand calculators.

To this end, a number of computer programs has been written, as outlined in Appendix 1. They have been made available on the Worldwide Web internet and may be accessed at web site www.cup.cam.ac.uk; the set of programs, with notes, may be obtained also from the author.