CO2 System Hydration and Dehydration Kinetics and the Equilibrium CO2/H2CO3 Ratio in Aqueous NaCl Solution

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Carbonic acid, Hydration, Dehydration, Carbon dioxide system, Kinetics

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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 equationlnkD(s−1)=30.15−(8018)T−1,">lnkD(s−1)=30.15−(8018)T−1, and the ionization constant, Ka, for H2CO3 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 (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 equationlnkH(s−1)=22.66−(7799)T−1.">lnkH(s−1)=22.66−(7799)T−1.

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Marine Chemistry, v. 78, issue 2-3, p. 65-73