Invariant expressions for linear complex mechanisms: Single-step substance case

Abstract We generalize the results on invariances found for linear two-step mechanisms within our joint kinetics approach. A general invariant expression for any linear complex mechanism with at least two single-step substances is obtained, from corrected ratios of the concentration profiles of single-step substances. The invariant expression consist of the product of three factors of different nature: • A non-thermodynamic factor: the ratio of kinetic coefficients of different chemical reactions. • A thermodynamic factor: the pure or apparent equilibrium constant of a sub-mechanism within the complex mechanism. • An “experimental” factor, defined by the initial conditions of the two experiments needed to determine the invariant expression. The relationship between the structure of the linear complex mechanism and the peculiarities of the invariant expression obtained are presented. A mathematical demonstration of the invariant expression is given. The demonstration is based on an invariant expression from reciprocal experiments, related to Onsager’s reciprocal relations.