The present monograph appears after the death of Professor V. N.
Kondratiev, one of those scientists who have greatly contributed to the
foundation of contem- porary gas kinetics. The most fundamental idea of
chemical kinetics, put for- ward at the beginning of the twentieth
century and connected with names such as W. Nernst, M. Bodenstein, N. N.
Semenov, and C. N. Hinshelwood, was that the complex chemical reactions
are in fact a manifestation of a set of simpler elementary reactions
involving but a small number of species. V. N. Kondratiev was one of the
first to adopt this idea and to start investigations on the elementary
chemical reactions proper. These investigations revealed explicitly that
every elementary reaction in turn consisted of many elementary events
usually referred to as elementary processes. It took some time to
realize that an elementary reaction, represented in a very simple way by
a macroscopic kinetic equation, can be described on a microscopic level
by a generalized Boltzmann equation. Neverheless, up to the middle of
the twentieth century, gas kinetics was mainly concerned with the
interpretation of complex chemical reactions via a set of elementary
reactions. But later on, the situation changed drastically. First, the
conditions for reducing microscopic cquations to macroscopic ones were
clearly set up. These are essentially based on the fact that the small
perturbations of the Maxwell-Boltzmann distribution are caused by the
reaction proper.