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.

The thermodynamic properties of sodium uranoborate

Abstract: The standard enthalpy of formation of crystalline NaBUO 5 at 298.15 K (-2257.5 ′ 4.0 kJ/mol) was determined by reaction calorimetry. The heat capacity of the substance in the temperature range 10-300 K was studied by adiabatic vacuum calorimetry. The thermodynamic functions of the compound were calculated. The standard entropy and the Gibbs function of formation of sodium uranoborate at 298.15 K were found to be -452.7 ′ 2.1 J/(mol K) and -2122.5 ′ 4.5 kJ/mol, respectively. The standard thermodynamic functions of synthesis and thermal decomposition of sodium uranoborate were calculated and analyzed.

The rare earth ruthenium pyrochlore Ho2Ru2O7(s): thermodynamic properties by electrochemical cell and differential scanning calorimetric measurements

Abstract: The Gibbs energy of formation of Ho2Ru2O7(s) has been determined by employing a solid-state electrochemical cell incorporating an oxide ion conducting electrolyte. The reversible electromotive force (e.m.f.) of the following cell has been measured: cell: (−)Pt/{Ho2O3(s) + Ho2Ru2O7(s) + Ru(s)}//CSZ//O2(p(O2) = 21.21 kPa)/Pt(+). The Gibbs energy of formation of Ho2Ru2O7(s) from elements in their standard state, calculated by the least squares regression analysis of the data obtained in the present study, can be given by: {ΔfG°(Ho2Ru2O7,s)/(kJ mol−1) ± 2.6} = −2518.6 + 0.6225(T/K); (937 ≤ T/K ≤ 1265). The standard molar heat capacity C°p,m(T) of Ho2Ru2O7(s), was measured using a heat flux type differential scanning calorimeter (DSC) in the temperature range from 307 K to 765 K. The heat capacity was fitted into a mathematical expression and can be represented by: C°p,m((Ho2Ru2O7,s,T) (J K−1 mol−1)) = 289.8 + 3.06 × 10−2T (K) − 33.74 × 105/T2 (K); (307 ≤ T (K) ≤ 765). The heat capacity data of Ho2Ru2O7(s), along with the data obtained from the oxide electrochemical cell were used to calculate the standard enthalpy of formation and absolute molar entropy of the compound.

Solubility Measurements and Thermodynamic Properties of Sorbic Acid in Binary Solvent Mixtures of (Ethanol, 1-Propanol or 2-Propanol + Water) from 283.15 to 323.15 K

Abstract: The solubility data of sorbic acid in binary systems of (ethanol + water), (1-propanol + water) and (2-propanol + water) were measured from 283.15 to 323.15 K using the static equilibrium method under atmospheric pressure. It was found that the solubility of sorbic acid in the three binary solvent systems increased with increasing temperature as well as increasing initial mole fraction of organic solvent in these systems. The van’t Hoff–Jouyban–Acree model, the modified Apelblat–Jouyban–Acree model and the CNIBS/R-K model were proposed for correlating the experimental solubility values in various solution systems. Furthermore, the dissolution thermodynamic properties of Gibbs energy change (ΔsolGo), molar enthalpy change (ΔsolHo) and molar entropy change (ΔsolSo) were calculated from the experimental solubility data, using the van’t Hoff equation. The positive values of ΔsolGo, ΔsolHo and ΔsolSo indicate that these dissolution processes of sorbic acid in the solvents studied were all endothermic and entropically favorable. In addition, the change of dissolution enthalpy was the main contributor to the positive value of the molar Gibbs energy of the dissolution process. The experimental solubility and the models used in this work would be conducive to purifying sorbic acid from its crude mixtures.

Adsorption of 4 He on neon-coated exfoliated graphite

Abstract: Adsorption isotherms of 4He on Grafoil coated with a monolayer of neon were made for the temperature range of 2–10 K and in the pressure range of 0.10–15.00 Torr, using a standard volumetric method. From these isotherms the isosteric heats of adsorption were calculated as a function of coverage. The binding energy of 4He on Ne was obtained from the isosteric heat for V → 0, yielding a value of 39.4 K. The differential molar entropy and the internal molar energy were calculated as a function of coverage. A comparison of monolayer coverage obtained by analyzing different procedures is presented. Whenever possible the results are compared with theoretical evaluations and previous experimental data.

Thermodynamics of Adsorption and Micellization of Triblock Copolymers of Oxyethylene and Oxybutylene in Aqueous Medium Using Surface Tensiometry

Abstract: The aqueous solutions of three triblock copolymers based on polyoxyethylene and polyoxybutylene of the type EmB10Em have been analyzed by surface tension measurements. Surface activity of these triblock copolymers was studied by measuring surface parameters, like surface excess concentration, Γ2, area per molecule of polymer and standard Gibb's free energy of adsorption, ΔoGads, at various temperatures in the range of 20 to 50°C. The Effect of block length of hydrophilic portion of triblock copolymers on surface activity was investigated in this work. Miceller behavior of these triblock copolymers was also investigated using above technique. Critical micelle concentration (CMC) was determined from the plot of surface tension versus log of concentration in the range of temperature of 20–50°C. Thermodynamic parameters, standard free energy of micellization, ΔoGmic, standard enthalpy of micellization, ΔoHmic, and standard entropy of micellization, ΔoSmic were calculated from CMC value using closed associatio...