CO2 system hydration and dehydration kinetics and the equilibrium CO2/H2CO3 ratio in aqueous NaCl solution

Observations of pH on a millisecond time scale were used to obtain the CO2 hydration rate, the H2CO3 dehydration rate, the ionization constant of H2O3, and the equilibrium ratio Of CO2 and H2CO3 concentrations over a range of temperature (15 - 32.5 degreesC. In 0.65 molal NaCl, close to the ionic strength of seawater, the H2CO3 dehydration rate constant (k(D)) is well represented by the equation lnk(D) (s(-1)) = 30.15 - (8018)T-1, and the ionization constant, K-D for H2CO3 followed the relationship logK(a) = -0.994 - (610.5)T-1, where T is the temperature (Kelvin scale). The equilibrium ratio (K-D) of CO2 and H2CO3 concentrations at 25 degreesC was equal to 848. K-D ranged from approximately 840 at 15 degreesC to 878 at 32.5 degreesC. Values of K-D and k(D) were used to calculate the CO2 hydration rate constant, k(H). Over the temperature range of this work, k(H) was well represented by the equation lnkH (s(-1)) = 22.66 - (7799)T-1. (C) 2002 Elsevier Science B.V. All rights reserved.