Thermodynamics of aqueous association and ionization reactions at high temperatures and pressures

Journal Article · Mon Aug 01 04:00:00 EDT 1988 · J. Solution Chem.; (United States)

DOI:https://doi.org/10.1007/BF00647417· OSTI ID:6084304

Mesmer, R E; Marshall, W L; Palmer, D A; Simonson, J M; Holmes, H F

Electrochemical and electrical conductance cells have been widely used at ORNL over the years to quantitatively determine equilibrium constants and their salt effects to 300/sup 0/C (EMF) and 800/sup 0/C (conductance) at the saturation pressure of water (EMF) and to 4000 bars (conductance). The most precise results to 300/sup 0/C for a large number of weak acids and bases show very similar thermodynamic behavior, which will be discussed. Results for the ionization constants of water, NH/sub 3/(aq), HCl(aq), and NaCl(aq), which extend well into the supercritical region, have been fitted in terms of a model with dependence on density and temperature. The entropy change is found to be the driving force for ion-association reactions and this tendency increases (as it must) with increasing temperature at a given pressure. Also, the variation of all thermodynamic properties is greatly reduced at high fixed densities. Considerable variation occurs at low densities. From this analysis, the dependence of the reaction thermodynamics on the P-V-T properties of the solvent is shown, and the implication of large changes in hydration for solutes in the vicinity of the critical temperature will be discussed. Finally, the change in the molar compressibility coefficient for all reactions in water is shown to be the same and dependent only on the compressibility of the solvent.

• Research Organization: Oak Ridge National Lab., TN (USA)
• DOE Contract Number: AC05-84OR21400
• OSTI ID: 6084304
• Journal Information: J. Solution Chem.; (United States), Journal Name: J. Solution Chem.; (United States) Vol. 17:8; ISSN JSLCA
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
400400 -- Electrochemistry
ALKALI METAL COMPOUNDS
AMMONIA
BASES
BINDING ENERGY
CHLORIDES
CHLORINE COMPOUNDS
COMPRESSIBILITY
DENSITY
ELECTRIC CONDUCTIVITY
ELECTRICAL PROPERTIES
ELECTROCHEMICAL CELLS
ENERGY
ENTHALPY
ENTROPY
EQUILIBRIUM
HALIDES
HALOGEN COMPOUNDS
HYDRATION
HYDRIDES
HYDROCHLORIC ACID
HYDROGEN COMPOUNDS
INORGANIC ACIDS
IONIZATION POTENTIAL
MATERIALS TESTING
MATHEMATICAL MODELS
MECHANICAL PROPERTIES
NITROGEN COMPOUNDS
NITROGEN HYDRIDES
OXYGEN COMPOUNDS
PH VALUE
PHYSICAL PROPERTIES
SODIUM CHLORIDES
SODIUM COMPOUNDS
SOLVATION
SOLVENTS
SULFURIC ACID
TEMPERATURE DEPENDENCE
TESTING
THERMODYNAMIC PROPERTIES
THERMODYNAMICS
TUNGSTATES
WATER