Showing papers on "Standard molar entropy published in 1971"

Methanol: Heat Capacity, Enthalpies of Transition and Melting, and Thermodynamic Properties from 5–300°K

Abstract: Thermal properties of methanol were studied by adiabatic calorimetry. The first‐order nature of the phase transition at 157.4°K with an entropy increment of 0.97 cal mole−1·°K−1 was confirmed. The heat capacity of the crystalline phase stable just below the triple point was defined and shown to be extremely sensitive to impurity. No evidence for a second previously‐reported phase transition could be detected. The standard entropy (S°) and Gibbs energy function (− [G° − H°0] / T) for the liquid at 298.15°K are 30.40 and 15.18 cal mole−1·°K−1, respectively. The proposed classification of methanol as a plastic crystal on the basis of its small entropy of melting (4.38 cal mole−1·°K−1) is considered with respect to hydrogen bonding in the liquid phase.

Sodium-Lithium Exchange Equilibria on Vermiculite at 25° and 50°C*

Abstract: Sodium-lithium exchange equilibria between dilute aqueous chloride solutions and 0.2–62 µ Transvaal, South African vermiculite were studied at 25° and 50°C using a dialysis technique. The K content of the vermiculite was reduced to < 1% of the exchange capacity of 2·14 me/g by exhaustive extraction using Na-tetraphenylboron. The thermodynamic equilibrium constants and in turn the standard free energies and heats of exchange were evaluated from the equilibrium selectivity coefficients at the two temperatures. The standard entropy of exchange, ΔS°, was calculated according to the relationship ΔG° = ΔH° − TΔS°. Similar results were obtained for Na → Li and Li → Na exchange at 25°C, thus confirming the reversibility of the reaction. Sodium preference increased with Na saturation of the vermiculite and equilibrium selectivity coefficients ranged from 6·0 to 22·0 at 25°C. In comparison, selectivity coefficients for Na-Li exchange on montmorillonite ranged from 1·0 to 2·0 and became smaller with increasing Na saturation. The standard free energy and heat of exchange on vermiculite at 25°C were −1444 and −5525 cal mole−1, respectively, resulting in a ΔS° value of −13·7 e.u. This relatively large entropy change is probably due to differences in ion hydration in the solution and surface phases.

Thermodynamic Properties of RuO2

Abstract: The free energy change for the reaction RuO2(s)+4Cu(s) = 2Cu2O(s)+Ru(s) was determined from 600° to 1000°C from emf measurements on a solid oxide galvanic cell using a stabilized ZrO2 electrolyte. The cell was designed to minimize the reduction of RuO2 by the gas phase. The results were used to develop an equation for the standard molar free energy of formation of RuO2: The standard molar enthalpy and entropy of formation of RuO2 at 298°K were calculated to be −72,430 ±200 cal/mol and –40.44±0.2 eu, respectively, using the available heat capacity data. The absolute entropy of RuO2 at 298°K was calculated to be 15.46±0.2 eu.

Calorimetric Study of Iodine Pentafluoride: Heat Capacity between 5 and 350°K, Enthalpy of Fusion and Vaporization, Standard Entropy of the Vapor, and Other Thermodynamic Properties

Abstract: The heat capacity of iodine pentafluoride has been measured by an adiabatic method between 5 and 350°K. The triple point of the compound is 282.553 ± 0.01°K and the enthalpy of fusion is ΔHfusion = 11222 ± 11 J mole−1. The vapor pressure measured between 283 and 378°K is represented by the equation: log10PmmHg = − 3090.14 / T − 6.96834 log10T + 29.02167. A determination of the vapor density at 330 and 372°K resulted in the values − 2813 and − 1232 cm3 mole−1, respectively, for the second virial coefficient B to be used with the equation of state PV = RT + BP. The enthalpy of vaporization at 330°K was calculated to be ΔHvap(330°K) = 39320 ± 200 J mole−1. At 298.15°K the standard state values of the thermodynamic functions obtained from the heat capacity data are: CP° = 174.7 ± 0.17 J °K−1·mole−1, S° = 224.85 ± 0.22 J °K−1·mole−1, (H° − H°0) = 37086 ± 37 J mole−1, and (G° − H°0) / T = − 100.47 ± 0.1 J °K−1·mole−1. The standard entropy of iodine pentafluoride vapor at 330°K calculated from calorimetric data ...