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  • 1
    ISSN: 1572-8927
    Keywords: Equilibrium constant ; Henry's constant ; enthalpy change ; entropy change ; heat capacity change ; flow calorimetry ; high temperature ; carbon dioxide ; carbonic acid ; sodium hydroxide ; sodium carbonate ; isocoulombic reaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The phase equilibrium CO2(g)=CO2(aq) and the aqueous reactions CO 3 2− +H+=HCO 3 − , HCO 3 − +H+=CO2(aq)+H2O, and Na++CO 3 2− =NaCO 3 − were studied from 225 to 325°C using a flow calorimetric technique. Heats of mixing of gaseous CO2 with liquid H2O and with aqueous NaOH solutions were measured at these temperatures. Log K, ΔH, ΔS, and ΔCp values were determined for these reactions from the heat of mixing data. Equations for these thermodynamic quantities valid at infinite dilution (I=0) and 12.4 MPa are given as a function of temperature from 225 to 325°C. The log K and ΔH values agree well with literature values at these temperatures for the first and third reactions, but not for the second reaction. No previous results have been reported for the fourth reaction at high temperatures. The isocoulombic reaction principle is tested using the log K values determined in this study. This principle is found to be valid for the reactions where each charge on one side of the equation is balanced on the other side by a charge of the same sign and magnitude, but not for the reaction where two single negative charges (HCO 3 − and OH−) are balanced by one double negative charge (CO 3 2− ).
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1572-8927
    Keywords: Dilution enthalpies ; activity coefficient ; alkali metal chlorides ; equilibrium constants ; enthalpy changes ; entropy changes ; heat capacity changes ; high temperature ; aqueous solution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Dilution enthalpies, measured using isothermal flow calorimetry, are reported for aqueous solutions of LiCl, KCl, and CsCl at 300°C and 11.0 MPa, 325°C and 14.8 MPa, and 350°C and 17.6 MPa. The concentration range of the chloride solutions was 0.5 to 0.02 m. Parameters for the Pitzer excess Gibbs ion-interaction equation were determined from the fits of the experimental heat data. Equilibrium constants, enthalpy changes, entropy changes, and heat capacity changes for ion association of the chloride salts were estimated from the heat data. For all systems, the enthalpy and entropy changes were positive and had accelerating increases with temperature. The resulting equilibrium constants show significant, but smaller, increases with temperature.
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  • 3
    Electronic Resource
    Electronic Resource
    Springer
    Journal of solution chemistry 26 (1997), S. 47-61 
    ISSN: 1572-8927
    Keywords: Dilution enthalpies ; activity coefficient ; alkali metal chlorides ; equilibrium constants ; enthalpy changes ; entropy changes ; heat capacity changes ; high temperature ; aqueous solution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Dilution enthalpies, measured using isothermal flow calorimetry, are reported for aqueous solutions of LiCl, KCl, and CsCl at 300°C and 11.0 MPa, 325°C and 14.8 MPa, and 350°C and 17.6 MPa. The concentration range of the chloride solutions was 0.5 to 0.02m. Parameters for the Pitzer excess Gibbs ion-interaction equation were determined from the fits of the experimental heat data. Equilibrium constants, enthalpy changes, entropy changes, and heat capacity changes for ion association of the chloride salts were estimated from the heat data. For all systems, the enthalpy and entropy changes were positive and had accelerating increases with temperature. The resulting equilibrium constants show significant, but smaller, increases with temperature.
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  • 4
    Electronic Resource
    Electronic Resource
    Springer
    Journal of solution chemistry 27 (1998), S. 183-194 
    ISSN: 1572-8927
    Keywords: Dilution enthalpies ; activity coefficients ; alkali metal hydroxides ; equilibrium constants ; enthalpy changes ; entropy changes ; heat capacity changes ; high temperature ; aqueous solution
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract Dilution enthalpies, measured using isothermal flow calorimetry, are reported for aqueous solutions of KOH and CsOH at 300°C and 11.0 MPa, 325°C and 14.8 MPa, and for aqueous solutions of NaOH, KOH, and CsOH at 350°C and 17.6 MPa. Previously collected dilution enthalpies for aqueous solutions of NaOH at 300°C and 9.3 MPa and at 325°C and 12.4 MPa were included when fitting the Pitzer parameters. The concentration range of the hydroxide solutions was 0.5–0.02 molal. Parameters for the Pitzer excess Gibbs ion-interaction equation were determined from the fits of the experimental heat data. Equilibrium constants, enthalpy changes, entropy changes, and heat capacity changes for alkali metal ion association with hydroxide ion were estimated from the heat data. For all systems, the enthalpy changes and entropy changes were positive and had accelerating increases with temperature. The resulting equilibrium constants show significant, but smaller, increases with temperature.
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  • 5
    Electronic Resource
    Electronic Resource
    Springer
    Journal of solution chemistry 23 (1994), S. 747-768 
    ISSN: 1572-8927
    Keywords: Enthalpy change ; ionization of water ; high temperature ; flow calorimetry ; thermodynamic quantities
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract 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°, ΔC p ° 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°, ΔC p ° , 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.
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  • 6
    ISSN: 1572-8927
    Keywords: Equilibrium constant ; enthalpy change ; entropy change ; heat capacity change ; flow calorimetry ; high temperature ; formation of water ; formation of sodium hydroxide ; isocoulombic reaction
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The aqueous reactions H++OH−=H2O at 325°C and Na++OH−= NaOH(aq) at 250–325°C, were studied using a flow calorimeter. Heats of mixing of aqueous NaOH and HCl solutions were measured at 325°C. The enthalpy of water formation (ΔH=95.9 kJ-mol−1, valid at 12.4 MPa and infinite dilution) was obtained at this temperature from the heat of mixing data but differs significantly from that calculated from the Marshall-Franck equation. This calorimetric ΔH at 325°C was used in combination with literaturelog K and ΔH values at lower temperatures to derive equations representinglog K, ΔH, ΔS, and ΔCp for the formation of water from 250 to 325°C. Heats of dilution of aqueous NaOH solutions were measured at 250, 275, 300, and 325°C. Log K, ΔH, and ΔS for the formation of NaOH(aq) were determined at these temperatures from the fits of the calculated and measured heats while ΔCp values were calculated from the variation of ΔH with temperature. No previous experimental results have been reported for the formation of NaOH(aq). The isocoulombic reaction principle is tested using thelog K values obtained in this study. The plot oflog K vs. 1/T for the isocoulombic reaction NaOH(aq) +H+=H2O+Na+ is approximately linear.
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