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 CO ₂ hydration rate, the H ₂ CO ₃ dehydration rate, the ionization constant of H ₂ CO ₃ , and the equilibrium ratio of CO ₂ and H ₂ CO ₃ concentrations over a range of temperature (15–32.5 °C). In 0.65 molal NaCl, close to the ionic strength of seawater, the H ₂ CO ₃ dehydration rate constant ( k _D ) is well represented by the equationlnkD(s−1)=30.15−(8018)T−1,">lnkD(s−1)=30.15−(8018)T−1, and the ionization constant, K _a , for H ₂ CO ₃ followed the relationshiplogKa=−0.994−(610.5)T−1,">logKa=−0.994−(610.5)T−1, where T is the temperature (Kelvin scale). The equilibrium ratio ( K _D ) of CO ₂ and H ₂ CO ₃ concentrations at 25 °C was equal to 848. K _D ranged from approximately 840 at 15 °C to 878 at 32.5 °C. Values of K _D and k _D were used to calculate the CO ₂ hydration rate constant, k _H . Over the temperature range of this work, k _H was well represented by the equationlnkH(s−1)=22.66−(7799)T−1.">lnkH(s−1)=22.66−(7799)T−1.