INFLUENCE OF THE AUTOCATALYTIC STAGES ON THE DYNAMICS OF CONJUGATED CHEMICAL REACTIONS

Abstract

Chemical reactions occurring on nonlinear mechanisms, containing the stage of interaction of various reagents (feedback), can exhibit unusual kinetic properties - the multiplicity of equilibria (hysteresis of different shape dependency on the «velocity-parameter»), change the time of the motion to the equilibrium (slow or fast relaxation), sustained oscillations (regular, irregular), etc. All these critical phenomena are usually associated with the appearance of unstable equilibria in the reactions under study. From the kinetic point of view, one of the main causes of instability is the presence of autocatalytic stages in the reaction mechanism. Therefore, it is interesting to study the effect of autocatalytic stages on the kinetics of chemical reactions, especially far from equilibrium. In this regard, the dynamic characteristics of typical conjugate reactions occurring by non-autocatalytic and autocatalytic mechanisms in an isothermal reactor of ideal mixing under the same conditions are compared in this paper. It is shown that the kinetics of these reactions is different: autocatalysis can shift the equilibrium, change the relaxation time and the rate of reactions. In an irreversible consecutive reaction (far from equilibrium) autocatalysis shifts the equilibrium in the direction of increasing the proportion occupied by the surface of the catalyst and the reaction rate dominated by positive autocatalysis. As the reversible processes increase, the balance shifts to the other side, the reaction slows down and autoinhibition begins to prevail. In parallel conjugate reactions, negative autocatalysis is not observed. In both types of the considered conjugate reactions, the maximum positive change in concentrations and velocity due to autocatalysis observed when these reactions are irreversible.