Reconstruction of Reversible Reaction Theory from the Perspective of the Second Law of Thermodynamics: Experimental Verification Based on the Definition of Chemical Equilibrium

Traditional chemical equilibrium theory posits that reversible reactions can achieve bidirectional dynamic equilibrium under identical thermodynamic conditions. However, this assumption fundamentally contradicts the unidirectionality constraint of the second law of thermodynamics (ΔrG). Through theoretical analysis and systematic experiments, this study reveals the inherent logical paradox in the traditional definition of reversible reactions: if both forward and reverse reactions must satisfy the spontaneous condition of ΔrG < 0, they directly violate the second law of thermodynamics. Based on thermodynamic calculations for typical cases such as water electrolysis and calcium carbonate decomposition, as well as unidirectionality evidence from experiments like ethyl acetate saponification and sucrose hydrolysis, this paper confirms that chemical reactions proceed unidirectionally only under specific thermodynamic conditions. The reaction endpoint is determined by reactant depletion or kinetic stagnation, rather than dynamic equilibrium. Isotope tracing technology further validates the unidirectional characteristics at the microscopic level. Accordingly, this study proposes a revised model: the essence of reversible reactions lies in switching reaction directions by altering thermodynamic conditions (e.g., temperature, pressure, concentration), rather than achieving bidirectional dynamic equilibrium under the same conditions. The findings challenge the core assumptions of traditional chemical equilibrium theory and offer a new perspective for the theoretical integration of thermodynamics and reaction kinetics.