Standard molar entropy

About: Standard molar entropy is a research topic. Over the lifetime, 1586 publications have been published within this topic receiving 29886 citations.

Molar entropy of the selenium (VI)/(IV) couple obtained by cyclic voltammetry

Abstract: An electrochemical investigation of selenium species, using cyclic voltammetry, has been carried out for the purpose of determining the molar entropy of the Se(VI)/(IV) couple. To obtain the ion interaction coefficient between HSeO4− and Na+, ϵT(HSeO4−, Na+), the following reaction involving HSeO4− as an oxidant and the uncharged species (H2SeO3) as the reductant was used: The Se(VI)/(IV) half-wave potentials were measured in acidic sodium nitrate solutions as a function of the molality of Na+ ranging from 0.500 to 2.00 mol kg−1. The temperatures for the measurement were 288, 298, 308 and 323 K. Specific ion interaction theory was used to calculate the HSeO4−/H2SeO3 standard redox potential, , and ϵT(HSeO4−, Na+) at each temperature. The following molar entropy was derived from the temperature dependence of : The value of ϵT(HSeO4−, Na+) at 298 K was determined to be 0.29 ± 0.03 kg mol−1. The following ∂ϵ/∂T was derived from the temperature dependence of ϵT(HSeO4−, Na+):

Na2O activity and thermodynamic mixing properties of SiO2–Na2O–CaO melt

Abstract: Electro-motive force (EMF) measurement using concentration cell with direct contact between sample and reference melts has been carried out to determine the Na 2 O activity of silicate melt. Thermodynamic mixing properties of silicate melts have been examined based on the temperature and compositional dependences of the Na 2 O activity. The Na 2 O activities for soda silicate melt and soda aluminosilicate melt measured by the method of this study are in agreement with previously reported values. The Na 2 O activities for (100 − x − y)SiO 2 –xNa 2 O–yCaO (x = 12–30; y = 5–22, mol%) melts have been measured between 1273 K and 1573 K. The Na 2 O activity increases with increasing Na 2 O and CaO content when the melt is a depolymerized composition. The effect of Na 2 O and CaO contents on the Na 2 O activity decreases with increasing SiO 2 content. They can be interpreted in terms of Gibbs energy of mixing as a concave function of composition. The comparison of partial molar entropy of mixing for soda-lime silicate and sodium silicate melts suggests the existence of local maximum of the entropy of mixing in depolymerized composition of SiO 2 –Na 2 O–CaO system. The effect of CaO on redox reaction of iron in silicate melt calculated from the Na 2 O activity is quantitatively consistent with that measured by voltammetry and wet-chemical analysis.

Solubility products, thermodynamic functions and stability constants for the praseodymium and ytterbium fluoride

Abstract: The solubility products and thermodynamic functions for the praseodymium and ytterbium fluoride-water systems have been measured using different analytical techniques for comparison among the measured values as well as with values reported in literature. Although there is not much difference among our values obtained by potentiometric, conductometric and radiometric methods, the values for PrFa disagree with at least two of the reported values. The effects of precipitant, aging of the precipitate and pH of the saturated solutions on the solubility product were studied and found to be significant. The standard enthalpy and free energy changes for the dissolution of both fluorides were found to be positive although the enthalpy for YbF~ is about twice as high as that for PrF 3 . The standard entropy change for PrF 3 is negative, but that for YbF 3 is positive. The overall stability constants for the monoand difluoride complexes of both Pr and Yb have also been measured potentiometrically using a simplified approach.

Thermodynamics of lutetium uranosilicate

Abstract: The standard enthalpy of formation of crystalline Lu(HSiUO6)3 · 10H2O at 298.15 K, −10668.0±16.0 kJ mol−1, and the standard enthalpy of its dehydration were determined by reaction calorimetry. The heat capacity of this compound in the range 80–300 K was measured by adiabatic vacuum calorimetry, and its thermodynamic functions were calculated. The standard entropy of formation at 298.15 K is −3812.9±1.2 J mol−1 K−1, and the standard Gibbs energy of formation at 298.15 K, −9531.0±16.5 kJ mol−1. The standard thermodynamic functions of the reactions of the synthesis of lutetium uranosilicate were calculated and discussed.

Entropy characteristics of adsorption of benzene derivatives from aqueous-methanol solutions on the graphite-like adsorbent

Abstract: Thermodynamics of adsorption of benzene and its various functional derivatives from aqueous-methanol solutions of different compositions was investigated by equilibrium adsorption HPLC on columns with porous graphitized carbon Hypercarb. A method was proposed for the determination of the molar standard entropy of the adsorptive in the state of a infinitely dilute solution in the eluent. The method makes use of the data of molecular statistical calculations of the equilibrium parameters of adsorption on the basal plane of graphite. Good agreement between values of entropy of the adsorptive in the eluent and entropy of pure liquid compounds is shown. It is concluded that solvation effects appear upon the interaction of molecules of the adsorptives and components of a binary solution.