Conditions for Satisfying the Second Law of Thermodynamics for Detailed and Reduced Chemical Mechanisms*

In this study, we establish the necessary and sufficient conditions for the automatic satisfaction of the second law of thermodynamics in chemical reactions. We provide a proof of the sufficiency of these conditions for both real and ideal gases. Furthermore, we consider the impact of these conditions on common mechanism reduction methods. One such technique for mechanism reduction is to transform a system of N reversible reactions into 2N irreversible reactions, followed by the elimination of reactions based on specific criteria. We demonstrate that neglecting reactions in this way generally leads to violations of the second law. The magnitude of these violations vary, depending on the specific set of reactions and conditions. Consequently, we discuss the merits and drawbacks of common mechanism reduction techniques in light of the preceding analysis. Additionally, we explore the implication of these results on achieving thermodynamic consistency while employing global mechanisms.