KINETICS QUASIINVARIANTS OF CHEMICAL REACTIONS IN CLOSED SYSTEMS
Abstract
The limitations of the dual-method and its extended version of the multi-experiment method in determining the exact time kinetic (thermodynamic) invariants and approximate invariants (quasiinvariants) of chemical reactions in closed isothermal systems are discussed. It is shown that for reactions, which allow except for internal equilibria, also boundary equilibria (multiple equilibria, multiequilibrium), for example, autocatalytic ones, there are always some "inconvenient" boundary values of reagent concentrations. These "uncomfortable" values cannot be used as the initial concentrations (conditions) for non-equilibrium multi-experiments (forward, reverse or intermediate), because for these values of non-equilibrium solutions cease to exist and, consequently, the reaction can proceed only in the equilibrium regime. As a result, the "usual " method of multi-experiments, using only the boundary values of the equilibrium concentrations of reagents, is not applicable. In this paper, a generalization of this method is proposed and a technique for conducting multi-experiments is developed, which is applicable for wider classes of reactions, including those with boundary equilibria, as well as autocatalytic reactions. This generalized method of multi-experiments (MME) allows one to bypass the limitations of the conventional multi-experiment method (dual-method) and to determine the exact time thermodynamic (kinetic) invariants of linear and some nonlinear chemical reactions, as well as approximate time invariants of any nonlinear chemical reactions in closed isothermal systems. The conditions of multi-experiments which are necessary for the correct operation of this method are determined. Examples of using the generalized method of multi-experiments for one-step and two-step nonlinear reactions with one and two independent reagents, respectively, are given. The kinetic time invariants and quasinvariants found with this method are compared with the exact solutions for the cases where they exist.
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