A general approach to the description of monomolecular reactions affected by random impacts has been developed on the basis of irreversible random transitions theory. Theoretical results derived allow us to account for concrete forms of stochastic affections and to evaluate statistical characteristics of reaction systems with monomolecular processes. Kinetic curves described in terms of the proposed theory provide information on certain properties of the random media. Such an approach gives a possibility to include both classical chemical kinetics and a polychromatic approximation as two limit cases. Exact solutions are given in two relevant cases in order to illustrate the applicability of the theory developed by the authors.