Sue E. Gillespie

Thermodynamic quantities for the interaction of SO 4 2? with H+ and Na+ in aqueous solution from 150 to 320C

AbstractThe aqueous reactions,

Thermodynamic quantities for the protonation of amino acid amino groups from 323.15 to 398.15 K

\begin{gathered} H^ + + SO_4^{2 - } = HSO_4^ - ,Na^ + + SO_4^{2 - } = NaSO_1^ - , \hfill \\ and H^ + + HSO_4^ - = H_2 SO_4 (aq) \hfill \\ \end{gathered}

Thermodynamic quantities for the interaction of Cl− with Mg2+, Ca2+ and H+ in aqueous solution from 250 to 325°C

were studied as a function of ionic strength(I) at 150, 175, 200, 250, 300 and 320°C using a flow calorimetric procedure. Log K, ΔH, ΔS and ΔCp values at I=0 were derived from the data at each temperature. Using these experimental values, equations describing log K, ΔH, ΔS and ΔCp at I=0 and temperatures from 150 to 320°C were derived for each system. The use of equations containing identical numbers of positive and identical numbers of negative charges on both sides of the equal sign (isocoulombic reaction principle) was evaluated as a technique for the extrapolation of log K values valid below 100°C to temperatures above 150°C. This evaluation indicated that the principle gives good estimates up to 320°C.

Determination of enthalpy of ionization of water from 250 to 350° C

The aqueous reactions, {ie865-1}were studied as a function of ionic strength at 275, 300, and 320°C using a flow calorimetric technique. Log K, ΔH and ΔS values were determined from the fits of the calculated and experimental heats while ΔCp values were calculated from the variation of ΔH values with temperature. The log K and ΔH values for the first two reactions agree well with literature values at these temperatures. No previous results have been reported for the third reaction. The use of equations containing identical numbers of positive and identical numbers of negative charges on both sides of the equal sign (isocoulombic reaction principle) was applied to the log K values determined in this study. The resulting plots of log K for the isocoulombic reactions vs. I/T were approximately linear, which demonstrates that the ΔCp values for these reactions are approximately zero.

Thermodynamic quantities for the ionization of nitric acid in aqueous solution from 250 to 319°C

Flow claorimetry has been used to study the interaction of protons with glycine, DL-α-alanine, β-alanine, DL-2-aminobutyric acid, 4-aminobutyric acid, and 6-aminocaproic acid in aqueous solutions at temperatures from 323.15 to 398.15 K. By combining the measured heats for amino acid solutions titrated with NaOH solutions with the heat of ionization for water, the log K, ΔHo, ΔSo, and ΔCpo values for the protonation of the amino groups of these amino acids have been obtained at each temperature studied. Equations are given expressing these values as functions of temperature. The ΔHo and ΔSo values increase while log K values decrease as temperacture increases. The trends for log K, ΔHo, ΔSo, and ΔCpo are discussed in terms of changes in long-range and short-range solvent effects. The trend in ΔHo, ΔSo, and ΔCpo values with temperature and with charge separation in the zwitterions is interpreted in terms of solvent-solute interactions and the electrostatic interaction between the two oppositely charged groups within the molecule.

Effect of temperature and pressure on the protonation of glycine.

Flow calorimetry has been used to study the interaction of glycine, DL-α-alanine, DL-2-aminobutyric acid, β-alanine, 4-aminobutyric acid, and 6-aminocaproic acid with protons in aqueous solutions from 323.15 K to 398.15 K and at 1.52 MPa. LogK, ΔH°, ΔS°, and ΔCp° for the protonation of the carboxylate groups of these amino acids have been obtained at each temperature studied. Equations are given expressing these values as functions of temperature. The protonation reactions are exothermic at lower temperatures and become endothermic as temperature increases. The logK, ΔH°, and ΔS° values are close together over the temperature range studied for the protonation of α-amino acids, i.e., glycine, DL-α-alanine, and 2-aminobutyric acid. At each temperature, the magnitudes of these thermodynamic quantities increase as the number of methylene groups between the amino group and the carboxylate group increases. The ΔCp° value for the protonation of the carboxyl group is found to lie between those of an isocoulombic reaction and a charge reduction reaction. At 323.15 K, the protonation reactions of the carboxylate groups have larger ΔCp° values which approach those associated with charge reduction reactions. As the temperature increases, ΔCp° decreases and approaches those found for isocoulombic reactions. This result is explained by considering long-range and short-range solvent effects. The trend in ΔH° and ΔS° with temperature and with charge separation in the zwitterions is interpreted in terms of solvent-solute interactions and the electrostatic interaction of the two oppositely charged groups within the molecule.

The effect of temperature and pressure on the protonation ofo-phosphate ions at 348.15 and 398.15 K, and at 1.52 and 12.50 MPa

The aqueous reactions, Mg2++Cl−=MgCl+, Ca2++Cl−=CaCl+, and H+ +Cl−=HCl(aq), were studied as a function of ionic strength at 250, 275, 300, and 325°C using a flow calorimetric technique. The logK, ΔH, ΔS and ΔCp values were determined from the fits of the calculated and experimental heast. The data were reduced assuming a known functionality of the activity coefficient. Hence, the logK, ΔH, ΔS and ΔCp values determined in this study are dependent on the activity coefficient model used. These thermodynamic values were compared with literature results. The logK values for the formation of MgCl+ agree reasonably well with those reported in the literature. The logK values for CaCl+ formation agree reasonably well with those reported in the literature at 300 and 325°C. At lower temperatures, the agreement is poorer. The logK values for the formation of HCl(aq) are generally lower than those reported in the literature. The logK, ΔH, ΔS and ΔCp values for all three ion association reactions are positive and increase with temperature over the temperature range studied. These values are the first determined calorimetrically for the formation of MgCl+ and CaCl+ in the temperature range 275–325°C.

Calorimetric determination of thermodynamic quantities for chemical reactions in the system CO2−NaOH−H2O from 225 to 325°C

The enthalpy changes at zero ionic strength (ΔH°) for the ionization of water (H2O=H++OH−) were determined by flow calorimetry from the heats of mixing of aqueous NaOH and HCl solutions in the temperature range 250 to 350°C. Pitzer ion-interaction models developed by other workers were used to calculate enthalpies of dilution of aqueous NaOH, HCl, and NaCl solutions for the extrapolation of ΔH values from the conditions of the experiment to infinite dilution. Equations are derived for thermodynamic quantities (log K, ΔH°, ΔS°, ΔCp° and ΔV°) for the ionization of water using the ΔH° values determined in this study from 250 to 350°C and literature log K and ΔH° values from 0 to 225°C. Smoothed values of log K, ΔH°, ΔS°, ΔCp°, and ΔV° are presented at rounded temperatures from 0 to 350°C and at the saturation pressure of water for each temperature. The equations in the present study provide a better representation of experimental thermodynamic data from 0 to 350°C than the Marshall-Franck equation.