Periodicity in chemically reacting systems. A model for the kinetics of the decomposition of Na2S2O4

Abstract

Sodium dithionite undergoes thermal decomposition in aqueous solution to form sodium bisulphite and sodium thiosulphate. It has been observed previously that in the decomposition, under some conditions, the concentration of the reactant oscillates in time. Although various theoretical mechanisms, such as the Lotka system, have been proposed which would produce oscillations in the rate of reaction and in the concentrations of intermediate species in a reacting system, none of the theoretical mechanisms can explain the oscillations, including periodic increases, of the reactant concentration observed in the dithionite system.

In this paper, the observed behaviour of the dithionite system is described. Three mechanisms are discussed which have been proposed by others to explain various characteristics, other than the oscillations, of the decomposition. It is then shown how these mechanisms could, with certain modifications, produce oscillations such as are observed with the dithionite system.