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

Abstract 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 equation ln k D ( s −1 )=30.15−(8018)T −1 , and the ionization constant, K a , for H 2 CO 3 followed the relationship log K a =−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 equation ln k H ( s −1 )=22.66−(7799)T −1 .