Some remarks on the application of relaxation techniques to chemical equilibria

About 40 years ago, relaxation techniques were developed by Eigen and cowor kers. These techniques provided a new and powerful method to investigate "f ast" reactions in solution. To apply these techniques, the system, after pe rturbation, should remain in a position close to equilibrium, so that the k inetic equations can be linearized. If the system is brought to a position far from equilibrium, the full system of dynamical equations should be cons idered. Here (experimentally feasible), oscillation and chaos may appear. B esides, the classical extension of relaxation techniques to stationary stat es is not so straightforward as usually stated in the literature on relaxat ion phenomena. Another possible problem of the classical approach to relaxa tion techniques comes from the analysis of the total concentration change i n normal modes of reaction. Normally, one or two of the relaxation times, c an be determined from the kinetic trace. However, all of them are responsib le for the total concentration change. Thus, a systematic error is associat ed with this procedure. For these reasons, the purpose of this article is t wofold. First, we point out these shortcomings and show the way to handle t hem, and, second, we propose the use of sensitivity analysis as a new metho d to extract thermodynamic information from relaxation experiments. (C) 200 0 Elsevier Science B.V. All rights reserved.