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 H2CO3, and the equilibrium ratio of CO2 and H2CO3 concentrations over a range of temperature (15–32.5 °C). In 0.65 molal NaCl, close to the ionic strength of seawater, the H2CO3 dehydration rate constant (kD) is well represented by the equation lnkD (s−1)=30.15−(8018)T−1,and the ionization constant, Ka, for H2CO3 followed the relationship logKa=−0.994−(610.5)T−1,where T is the temperature (Kelvin scale). The equilibrium ratio (KD) of CO2 and H2CO3 concentrations at 25 °C was equal to 848. KD ranged from approximately 840 at 15 °C to 878 at 32.5 °C. Values of KD and kD were used to calculate the CO2 hydration rate constant, kH. Over the temperature range of this work, kH was well represented by the equation lnkH (s−1)=22.66−(7799)T−1.