Essmaiil Djamali

A unified theory of the thermodynamic properties of aqueous electrolytes to extreme temperatures and pressures.

A new theoretical treatment has been developed for predicting the thermodynamic properties of electrolytes up to and beyond the critical temperature of water (973 K and at pressures up to 1000 MPa). The model is based upon the classical Born equation corrected for non-Born hydration effects. The temperature and pressure behavior of electrolytes can now be accurately predicted from existing low temperature data. Only two constants are needed for each electrolyte at all temperatures and pressures, where data exist to test the theory.

Standard State Thermodynamic Properties of Aqueous Sodium Chloride Using High Dilution Calorimetry at Extreme Temperatures and Pressures

In this communication, we report the first calorimetric data for the standard state enthalpies of a solution of sodium chloride obtained from high dilution, down to (10(-3) m), integral heats of solution measurements to 596.30 K. Although there are no comparable thermodynamic data available at such high dilutions in the literature, the present results for NaCl(aq) can be used for many thermodynamic studies by others to achieve a complete thermodynamic description of this key electrolyte over very wide ranges of concentration. From the recently developed unified theory of electrolytes, the experimental data from this study were used to predict Gibbs free energies of hydration of sodium chloride up to 1100 K. These Gibbs free energies of hydration at different pressures and densities compare well with reported values obtained from ab initio calculations by others.

A Priori Prediction of Thermodynamic Properties of Electrolytes in Mixed Aqueous–Organic Solvents to Extreme Temperatures

The unified theory of electrolytes (J. Phys. Chem. B 2009, 113, 2398-2404) for predicting the standard state thermodynamic properties of aqueous electrolytes has been extended to include mixed solvent systems. The solubility of solid sodium chloride in mixed solvents (methanol/water concentration up to 75% w/w) was also measured up to 466 K and pressures near 7 MPa. The present model, together with a simple modification of Pitzers thermodynamic treatment of aqueous solutions, allows a priori prediction of solubility of electrolytes in aqueous/organic systems to extreme temperatures and pressures. Solubility is predicted for sodium chloride and potassium chloride in mixed solvents (methanol/water, ethanol/water) over a wide range of temperatures and compositions from the extension of the unified theory of electrolytes to mixed solvents. Comparisons indicate good agreement in all cases to well within the uncertainties of the experimental data. The stoichiometric activity coefficients of saturated solution of sodium chloride in methanol/water mixed solvents were calculated up to 473.15 K. The stoichiometric activity coefficients, as a function of temperature at all concentrations (0 ≤ m ≤ m(sat)) and the entire range of mole fraction of methanol, were also calculated up to 473.15 K. The novelty of the present approach is that no additional parameters are required to account for the medium effect.

Standard state thermodynamic properties of completely ionized aqueous sodium sulfate using high dilution calorimetry up to 598.15 K.

Pabalan and Pitzer (Geochim. Cosmochim. Acta 1988, 52, 2393-2404) reported a comprehensive set of thermodynamic properties of aqueous solutions of sodium sulfate without using ion association or hydrolysis. However, there is now ample evidence available indicating that the ion association cannot be ignored at temperatures T>or=373 K. For example, even at the lowest concentration of their studies (m>or=0.05) and at 573.15 K, less than 20% of SO4(2-)(aq) is available as free ions. In the present study, the integral heats of solution of sodium sulfate were measured to very low concentrations (10(-4) m) up to 573.16 K. The data were analyzed correcting for the hydrolysis of SO4(2-)(aq) and the association of Na+(aq) with SO4(2-)(aq) and NaSO4-(aq) in order to obtain the final standard state thermodynamic properties of completely ionized aqueous sodium sulfate, Na2SO4(aq). From these and the available solubility data, the stoichiometric activity coefficients of saturated aqueous solutions of sodium sulfate were calculated up to 573.15 K and compared with literature data. The stoichiometric activity coefficients of aqueous solutions of sodium sulfate, as a function of temperature at all concentrations (0<or=m<or=msat), were also calculated up to 573.15 K.

Standard state thermodynamic properties of completely dissociated hydrochloric acid and aqueous sodium hydroxide at extreme temperatures and pressures.

Standard state thermodynamic properties for completely dissociated hydrochloric acid were fixed by ionic additivity, using the data from other strong electrolytes perrhenic acid, sodium perrhenate, and sodium chloride from 298.15 to 598.15 K and at p(sat). The standard electrode potential for the important silver-silver chloride electrode system and the equilibrium constants for the volatility of HCl from aqueous solutions were then calculated and compared with literature data. Using the experimental data from this study and auxiliary data from literature, the logarithm of the molal association constant of HCl at the critical temperature of water and at 673.15 K up to 1000 MPa was predicted from the unified theory of electrolytes (UTE). The standard state thermodynamic properties for completely dissociated aqueous sodium hydroxide were also calculated by ionic additivity over the same temperature range from aqueous sodium chloride, hydrochloric acid, and the dissociation constant of water. The results were compared with literature data.

Standard state thermodynamic properties of Ba2+(aq), Co2+(aq), and Cu2+(aq) up to 598.15 K, and temperature effect on ligand field.

Integral heat of solution measurements of barium chloride to 619.81 K, copper oxide in an excess of perrhenic acid to 585 K, and cobalt perrhenate in perrhenic acid to 573 K were measured in a high dilution calorimeter (< or =10(-3) m) at psat, from which the high temperature thermodynamic properties of aqueous barium chloride, copper perrhenate, and cobalt perrhenate were obtained. From the known differences between the corresponding properties for aqueous perrhenate and chloride ions, the thermodynamic properties of completely ionized aqueous copper and cobalt chloride were obtained from ionic additivity. The enthalpy and derived heat capacity data at higher temperatures (T > 473.15 K) suggest that the ligand field stabilization energy of Co2+(aq) may be disappearing.

Thermodynamic Properties of Aqueous Gadolinium Perrhenate and Gadolinium Chloride from High Dilution Calorimetry at Extreme Temperatures and Pressures

The heat of solution of solid cubic gadolinium oxide has been measured in noncomplexing perrhenic acid solutions at very high dilutions (10(-4) m) up to 596.30 K, from which the standard state thermodynamic properties of aqueous gadolinium perrhenate were determined up to 623.15 K. From the measured differences between similar properties of aqueous sodium chloride and perrhenate, thermodynamic properties for aqueous gadolinium chloride were obtained by ionic additivity. Data for the hydrolysis of Gd3+(aq) were obtained by separate determinations. The enthalpy of solution of gadolinium chloride at 623.15 K obtained from this research (-2.7 MJ mol(-1)) is apparently larger than any other recorded for a chemical reaction involving aqueous systems. Standard state partial molal heat capacities for ThCl4(aq) were predicted up to 623.15 K.

A high-temperature high-pressure calorimeter for determining heats of solution up to 623 K

A high-temperature high-pressure isoperibol calorimeter for determining the heats of solution and reaction of very dilute substances in water (10(-4) m) at temperatures up to 623 K is described. The energies of vaporization of water at steam saturation pressure were measured as a function of temperature and the results agree with the corresponding values from steam tables to better than 0.08+/-0.18%. The novelties of the present instrument relative to flow type heat capacity calorimeters are that measurements can be made at orders of magnitude lower concentrations and that measurement of heat of reaction involving solids or gases or in the presence of high concentrations of supporting electrolytes, acids, and bases is possible. Furthermore, the advantage of using enthalpy data over heat capacity data for calculations of the standard state Gibbs free energies of electrolytes is that the experimental heat data of this research need only be integrated once to derive higher temperature free energy data from lower temperatures. The derived heat capacities can be used mathematically to obtain free energies by double integration. However, the resulting errors are much smaller than if experimental aqueous heat capacities were used for the integrations.