N. N. SEMENOV. The Modern Theory of the Rates of Gaseous Chemical Reactions. (Series “The Newest Trends in Scientific Thought,” book 19. GIZ. Moscow—Leningrad, 1929. 127 pp. Price, bound, 1 ruble 28 kopecks.)

The physical chemistry of our time has advanced noticeably in comparison with classical physical chemistry. In connection with the development of the doctrine of the structure of atoms and molecules, a number of problems have arisen that are borderline in character between physics and chemistry. Among these, first of all, is the question of the mechanism of chemical reactions. Classical physical chemistry approached the chemical reaction chiefly from the side of its thermodynamic content. The phenomenological method of thermodynamics led to the equation of the isochore, to the doctrine of the coexistence of phases, etc. Even chemical kinetics formerly had rather a phenomenological character, since chemists in the field of the theory of reaction kinetics confined themselves to the general form of rate equations for reactions of equal orders. The complex attempts of certain theoretical physicists (Boltzmann and others) to approach questions of chemical kinetics by using the kinetic theory of gases and statistical mechanics did not reach chemists. Ostwald’s review of Boltzmann’s Gas Theory (a book in which a large chapter is devoted to the kinetic justification of the dissociation of gases) is known, describing it as Sisyphean labor that proved fruitless.

At the present time the situation has changed substantially. A number of well-conducted experimental studies have accumulated; a fairly large number of simple reactions in the gaseous medium have been studied, and a rather large body of quantitative material has been collected. Naturally, in connection with this there arose the need to interpret the results of experiments and to create a theory explaining kinetics as a function of the diverse conditions of reactions. Recently a known role in this has been played by the growing influence of catalytic reactions in chemical practice.

It is erroneous to think that chemical kinetics is a narrow, isolated chapter of physical chemistry, of interest only to those chemists who work scientifically in this field. Since the object of chemical investigation is the study of one reaction or another, it is clear that the question of how each elementary act of the process is carried out and how this affects the macroscopic picture of the phenomenon is an essential and, so to speak, pressing question. Most often, react—

...it is not an ordinary, stable, normal molecule that reacts, but a molecule in a special, excited, “pathological,” active state. To clarify this question of the nature of activation, the joint work of chemists with physicists is needed, physicists who command such delicate and precise methods as the spectroscopy of atoms and molecules. Further, kinetics also poses the second question: the course of a reaction in time and the conditions for the regeneration of active molecules. Not only in Russian, but also in the foreign literature, until comparatively recently there was no book treating these questions with sufficient completeness. Only a few years ago Hinshelwood’s book devoted to kinetics appeared, and only in the most recent books on statistical mechanics (Tolman, Fowler) is sufficient attention paid to the theory of chemical rate.

The book by N. N. Semenov must be recognized as timely, necessary, and useful. Above all, one feels that the author is writing about a subject close to him and well known to him. The interesting and valuable works of N. N. Semenov on the kinetics of explosive reactions and on the chain theory have found adequate reflection in the book under review. The question of activation is set forth clearly and intelligibly. The material is well chosen, beginning with the simple reactions of Polanyi, which proceed practically without any activation, and ending with the complex question of unimolecular reactions. The chapter on explosions is interesting. I think that in it chemists will find much that is new, since they have grown accustomed to regard all explosions as thermal. The exposition is lively and engaging, though not everywhere equally even. In some places the author is sufficiently popular (assuming in the reader only elementary knowledge), while in other places rather complicated formulas are given without derivation. Since the book is intended for the average chemist, it would not hurt to introduce at least a small chapter devoted to the elements of kinetic theory, giving in it the equation for the number of collisions and Boltzmann’s \(\varepsilon\)-law. The chapter on activation would do well to be supplemented by an indication of predissociation (V. Henri),¹ which is of great importance in the kinetics of reactions with polyatomic molecules. In substance the book is a small monograph and may prompt many to acquaint themselves with the subject in greater detail. One of the merits of the book is that it at once introduces the reader to the essence of the questions of kinetics and keeps him throughout at the level of contemporary achievements, without concealing difficulties and unsolved problems.

We wish the book success.

Ya. Syrkin.