Some remarks on the application of relaxation techniques to chemical equilibria Original Research Article

About 40 years ago, relaxation techniques were developed by Eigen and coworkers. These techniques provided a new and powerful method to investigate “fast” reactions in solution. To apply these techniques, the system, after perturbation, should remain in a position close to equilibrium, so that the kinetic equations can be linearized. If the system is brought to a position far from equilibrium, the full system of dynamical equations should be considered. Here (experimentally feasible), oscillation and chaos may appear. Besides, the classical extension of relaxation techniques to stationary states is not so straightforward as usually stated in the literature on relaxation phenomena. Another possible problem of the classical approach to relaxation techniques comes from the analysis of the total concentration change in normal modes of reaction. Normally, one or two of the relaxation times, can be determined from the kinetic trace. However, all of them are responsible for the total concentration change. Thus, a systematic error is associated with this procedure. For these reasons, the purpose of this article is twofold. First, we point out these shortcomings and show the way to handle them, and, second, we propose the use of sensitivity analysis as a new method to extract thermodynamic information from relaxation experiments.