Third dissociation constant of phosphoric acid in H₂O and D₂O from 75 to 300 °C at p = 20.4 MPa using Raman spectroscopy and a titanium-sapphire flow cell

Abstract

The first reported Raman spectra and ionization constants for the phosphate ion in H2O and D2O above 50 °C quantify deuterium isotope effects under hydrothermal conditions.

Second ionization constant of sulfuric acid in H2O and D2O from 150 to 300 °C at p = 11.5 MPa using flow AC conductivity

“…This expression demonstrated that changes in hydrogen bonding and the water coordination number at high temperature along with the drop in the light and heavy water dielectric constants would be expected to result in an increase in the Δp K a,m as it approaches the solvent critical points. 12 This prediction is consistent with the trend observed in the deuterium isotope effect on the bisulfate ionization reaction measured in this work, and by Yacyshyn et al , 22 further evidencing the validity of these results over those previously reported by Lietzke and Stoughton. 5…”

“…The deuterium isotope effect on chemical equilibrium constants has been reported in the literature for very few chemical systems at high temperatures. 5–12 As was described in the review by Laughton and Robertson, 2 a typical deuterium isotope effect is 0.2 > Δp K a,m > 1.0 at 25 °C with the general trend that the deuterium isotope effect increases with the acid p K a value. 4,76 As the temperature increases, the deuterium isotope effect on an acid ionization constant may increase or decrease, and the relative order of the effect between different acids is not preserved.…”

“…4,76 As the temperature increases, the deuterium isotope effect on an acid ionization constant may increase or decrease, and the relative order of the effect between different acids is not preserved. In previous work, 12 we developed a simple expression for the deuterium isotope effect as a function of temperature. This expression demonstrated that changes in hydrogen bonding and the water coordination number at high temperature along with the drop in the light and heavy water dielectric constants would be expected to result in an increase in the Δp K a,m as it approaches the solvent critical points.…”

“…1,2 The dissociation constants of weak acids are known to be larger in H 2 O than in D 2 O with a general trend of the difference being larger for weaker acids. 3,4 It is not well understood how these deuterium isotope effects change at high temperature and pressure because very few studies [5][6][7][8][9][10][11][12] exist in heavy water above B100 1C. In order to develop accurate thermodynamic models of heavy water systems at high temperatures, more experimental equilibrium constants and transport property data under these conditions are required.…”

Continuum Modeling of Porous Electrodes for Electrochemical Synthesis

“…It is once again important to note that the values of these rate constants have been shown to depend strongly on the local reaction environment. , For this reason, there is variance in the measured values for these rate constants. Additionally, these rate constants are dependent on the local electric field due to the second Wien effect (as discussed in section )a phenomenon which becomes particularly relevant in bipolar membranes or in the electrical double layer. − Proper models of electrochemical synthesis should aim to provide sensitivity analyses on the values of these rate parameters to account for the inconsistency in experimentally reported values.…”