The interaction of an organic
acid with
sodium bicarbonate in water produces an effervescent reaction. The reaction products are
carbon dioxide, water, and the
sodium salt of the
acid. The kinetic rate-determining step for this reaction is the
dehydration of
carbonic acid. The solid-solid interaction with known amounts of moisture was followed by quantitatively determining
carbon dioxide evolution as a function of time. The aqueous solubilities, diffusion coefficients, dissociation constants, and solid-solid interaction rates of six different substituted
benzoic acids were determined. Using a model based on diffusion of the organic
acid through the aqueous layer coupled with chemical reaction, predicted rates and levels of
carbon dioxide production were compared with experimental results. Included in the model were the effects of the reaction products on the
solution properties of the reactants. It was found that high concentrations of substituted
sodium benzoate were generated very quickly and affected the solubility of the reactants, diffusion coefficient of the
acid, and the
carbonic acid dehydration rate constant. Moisture content was found to have a profound influence on the interaction rate. Water provides a medium for diffusion of the reacting species as well as the reaction
solvent.