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Abstract  

Thermodynamic investigation of the extraction of both uranium(VI) and uranium(IV) from nitric acid solutions using tri-n-butyl phosphate (TBP) loaded on polyacrylic acid polymer (SM-7) as an inert supporting material has been done using batch technique. The effect of temperature on the equilibrium extraction values has been utilized to evaluate the change in standard thermodynamic quantities (viz. DH, DS, and DG). The Freundlich isotherm was successfully applied to the extraction data of both metal ions. The Dubinin-Radushkevich (D-R) isotherm was found to be valid only in case of U(IV) extraction. Based on the D-R expression, the maximum extraction capacity of loaded TBP and the mean free energy of U(IV) extraction have been determined.

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Abstract  

The protolytic equilibria in aqueous solutions of different amino acids and dipeptides were studied by a direct calorimetric method at 288–328 K. The measurements were made with an isothermal-shell calorimeter with automatic temperature recording. The thermodynamic characteristics of the processes of acid-base equilibria were found from the combined results of thermochemical measurements and equilibrium constant data. Gurney concepts were used to analyse the thermodynamic characteristics of reactions. Comparisons of the temperature-dependent and temperature-independent contributions to the Gibbs energy and enthalpy change afford the criteria of the variability in sign of the ΔH of the process, i.e. they allow prediction of the magnitude of the temperature θ at which ΔH = 0.

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Abstract  

A novel extractant, N, N-didecanoylpiperazine (DDPEZ), was synthesized for the first time. The extraction of U(VI) by DDPEZ from aqueous nitric acid media in carbon tetrachloride has been studied. The dependence of extraction distribution ratio on concentration of aqueous nitric acid, extractant, salting-out agent and temperature was investigated and the enthalpy of the extraction was calculated.

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Abstract  

Geometries and energies of isolated CaC2O4H2O, CaC2O4, CaCO3, CaO, H2O, CO and CO2 were determined at the ab initio level using effective core potential valence basis sets of doublezeta quality, supplemented with polarization functions. The effects of electron correlation were taken into account at the second order Mller-Plesset level of theory. For CaC2O4H2O, the correlation for the basis set superposition error was also included. Common routines were employed to evaluate entropies, heat capacities, as well as enthalpies and free enthalpies of formation of all entities. The enthalphies and free enthalpies of consecutive dehydration of CaC2O4H2O, decarbonylation of CaC2O4 and decomposition of CaCO3 towards CaO and CO2 were determined on the basis of avialable data from the literature or those predicted thoretically. Assuming that upon all the above mentioned processes the system maintains equilibrium, the fractions reacted, enthalpy changes and differential dependencies of thesevs. temperature were derived and compared with experimental thermoanalytical data.

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Abstract  

A novel system using a potassium aluminosilicate electrolyte under applied potential that is able to split H2O (or OH) into H2 and 1/2O2 (or O2 2-) with higher yields than the value deduced from Faraday"s law is presented. There were three steps by which H2 and O2 were generated stoichiometrically, and it was predicted that the high yields were due to the occurrence of chemically endothermic reactions: dehydration of the catalytic cell at a temperature below 100C (step I), disproportionation of KOH (2KOH→H2+K2O2) at a temperature around 200C (step II), and disproportionation of K2O (2K2O→K2+K2O2) at a temperature above 500C (step III). So-called Nemca might be caused in the course of step III, since the rate of H2 was ca 102 times larger than the value deduced from Faraday"s law.

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Summary In this paper we present excess molar volumes and excess molar enthalpies of binary and ternary mixtures containing propyl propanoate, hexane and cyclohexane as components at 298.15 K. Excess molar volumes were calculated from the density of the pure liquids and mixtures. The density was measured using an Anton Paar DMA 60/602 vibrating-tube densimeter. Excess molar enthalpies were obtained using a Calvet microcalorimeter

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