According to the acid-base proton theory, sodium lactate acts as a strong base and weak acid salt, while carbonic acid is a binary weak acid. When the two react, carbonic acid transfers protons to sodium lactate. At standard conditions of 25 ℃, the equilibrium constant of the reaction was experimentally determined to be approximately 0.056, indicating that the reaction can proceed spontaneously to some extent.
From the perspective of chemical kinetics, the rate of reaction between sodium lactate and carbonic acid is influenced by multiple factors. When the concentration of reactants is 0.1 mol/L, the reaction rate increases by about 1.5 times for every 10 ℃ increase in the reaction system temperature, which is consistent with the relationship between reaction rate and temperature described by the Arrhenius equation. The essence of this reaction is an ion exchange process, where lactate ions combine with hydrogen ions ionized from carbonic acid to form lactate, while carbonic acid ions combine with sodium ions. Some literature points out that in a solution with an ionic strength of 0.01, the activity coefficient of ions has an undeniable impact on the reaction process, which can cause deviations between the actual reaction situation and the ideal state. The reaction between sodium lactate and carbonic acid involves the principle of chemical equilibrium shift. When an appropriate amount of solid sodium chloride is added to the reaction system, the ion strength changes. According to the Debye Huck limit formula, the activity of ions will change, leading to a change in the equilibrium constant of the reaction, and the equilibrium will shift towards weakening this change. From the perspective of energy changes in the reaction, this reaction is an exothermic reaction. According to the calorimeter experiment, under the conditions of 101kPa and 298K, the amount of heat released per 1mol of lactic acid is about 28.5kJ. The release of this energy plays an important role in the temperature of the reaction system and the subsequent reaction process.
Considering the small secondary ionization constant of carbonic acid, it is mainly the primary ionization of carbonic acid that plays a role when reacting with sodium lactate. At 25 ℃, the first-order ionization constant of carbonic acid is 4.4 × 10 ⁻⁷, which determines the concentration of hydrogen ions that carbonic acid can provide in the reaction, thereby affecting the degree and direction of the reaction. There may be side reactions during the reaction between sodium lactate and carbonic acid. Due to its chemical activity with lactic acid, it may undergo its own polymerization reaction in the reaction system, especially under conditions of long reaction time and high temperature, the degree of this side reaction will increase. The reaction between sodium lactate and carbonic acid varies in different solvent systems. For example, in ethanol water mixed solvents, as the ethanol content increases, the solubility of sodium lactate and carbonic acid changes, resulting in a decrease in reaction rate. When the ethanol volume fraction reaches 50%, the reaction rate is only about 30% of that in pure water. The reaction product lactic acid exists in a certain dissociation equilibrium in solution. At 25 ℃, the dissociation constant of lactic acid is 1.38 × 10 ⁻⁴, which means that lactic acid will partially dissociate in the solution, affecting the acidity and alkalinity of the solution, and thus exerting feedback regulation on the subsequent process of the reaction.
From a microscopic perspective, the reaction between sodium lactate and carbonic acid is an effective collision process between molecules. According to collision theory, only molecules with sufficient energy and appropriate orientation can undergo a reaction through collision. In this reaction system, increasing the concentration of reactants or raising the temperature can increase the collision frequency and effective collision ratio of molecules, thereby accelerating the reaction rate.