Showing papers on "Standard molar entropy published in 1988"

Proportionality of Intrinsic Heat of Transport to Standard Entropy of Hydration for Aqueous Ions

Abstract: Intrinsic ionic heats of transport q * (ion) and ionic heats of transport Q * (ion) have been evaluated for 53 aqueous ions at infinite dilution at 25°C using the reduction rule proposed by the authors and the limiting laws of Agar, and of Helfand and Kirkwood without electrophoretic terms. q * (ion) have been found to correlate linearly with the standard ionic entropies of hydration for the 38 ions investigated. The correlation yields three distinctive proportionality constants indicating that the ions may be divided into three distinctive groups. Although the sign of Q * (ion) is not definite, all values of q * (ion) are positive. For 17 ions Q * (ion) are in good agreement with TS * (ion). Here, S * (ion) is the ‘absolute’ standard ionic entropy of transport which can be obtained from potentiometric measurements on cells. The values of S * (ion) were determined by Agar, and recently by Lin and coworkers.

Incommensurate phase transitions and anomalous lattice heat capacities of biphenyl.

Abstract: Heat capacities of crystalline biphenyl were measured between 3 and 300 K by adiabatic calorimetry and some thermodynamic functions including the calorimetric standard entropy were tabulated. Thermodynamic properties of the successive phase transitions were determined; for the twist transition at (40.4±0.2) K, ΔtrsH=(5.02±0.08) J·mol−1 and ΔtrsS=(0.129±0.003) J·K−1·mol−1, and for the lock-in transition at (16.8±0.1) K, ΔtrsH=(0.15±0.02) J·mol−1 and ΔtrsS=(0.009±0.001) J·K−1·mol−1. Anomalously large heat capacities at low temperatures were analyzed based on lattice dynamics calculation, and the crossover of the low temperature heat capacities of biphenyl and p-terphenyl was attributed to the greater activity of the twisting mode in biphenyl. The relation of the bond flexibility to the incommensurability is discussed through the comparison of the low temperature heat capacities of biphenyl, p-terphenyl, and 4,4′-difluorobiphenyl.

Thermochemistry of uranium compounds. XVI. Calorimetric determination of the standard molar enthalpy of formation at 298.15 K, low-temperature heat capacity, and high-temperature enthalpy increments of UO2(OH2)•H2O (schoepite)

Abstract: Three precise calorimetric methods, viz., low-temperature adiabatic, high-temperature drop, and solution-reaction, have been used to determine as a function of temperature the key chemical thermodynamic properties of a pure sample of schoepite, UO2(OH)2•H2O. The following results have been obtained at the standard reference temperature T = 298.15 K: standard molar enthalpy of formation molar heat capacity and the standard molar entropy The molar enthalpy increments relative to 298.15 K and the molar heat capacity are given by the polynomials: and , where 298.15 K < T < 400 K. The present result for at 298.15 K has been combined with three other closely-agreeing values from the literature to give a recommended weighted mean from which is calculated the standard Gibbs energy of formation at 298.15 K. Complete thermodynamic properties of schoepite are tabulated from 298.15 to 423.15 K.

Thermodynamics of molten Li-Sn alloys

Abstract: The activity of Li in molten Li-Sn alloys was continuously varied and monitored electrochemically in cells of the type Al-LiAl/glass electrolyte/Sn/glass electrolyte/Al-LiAl. The temperature (320 to 380 °C) and compositional dependence of the Li activity coefficient, γLi, was found to follow a quadratic expression of the form In γLi = A + B(1 − XLi)2 up to 30 mole pct lithium. Further, the liquidus temperature, TL, was found to follow TL(°C) = 642 XLi + 188 for 0.20 XLi 0.44 over the temperature range 320 to 470 °C. The partial and integral molar heats of solution were calculated and the results indicate that strong attractive forces exist between Sn and Li. These forces are strong enough to induce substantial ordering in the melt to an extent that the integral molar entropy of mixing at high Li contents (36 mole pct) is negative.

Thermodynamic parameters and shape of the mycobacterial polymethylpolysaccharide-fatty acid complex.

Abstract: Properties of the mycobacterial polymethylpolysaccharide-lipid complex have been investigated by fluorometric techniques. From the dissociation constant for the O-methyglucose polysaccharide-parinaric acid complex at 293 K, a Gibbs free energy (delta G degree) of -33.65 kJ/mol was obtained. The Kd decreased with increasing temperature, giving an enthalpy (delta H degree) of 15.4 kJ/mol. From these data, a molar entropy (delta S degree) of 167.4 J K-1 was obtained. Thus, the reaction is slightly endothermic, but the large positive entropy change leads to an overall negative free energy favoring complex formation. From fluorescence depolarization measurements, the methylglucose polysaccharide-parinaric acid complex appears to display isotropic rotation with a correlation time of 2.55 ns at 23 degrees C. This may be compared to a rotational correlation time of 6.17 ps for free parinaric acid in water at 23 degrees C calculated from the value determined in cyclohexanol at the same temperature, which demonstrates that the mobility of the fatty acid in the complex is restricted. Assuming the complex is spherical, it was calculated to have a diameter of 23-26 A, whereas a helical methyglucose polysaccharide molecule assembled from space-filling models has the dimensions of a cylinder of 18 X 24 A. The polysaccharide and fatty acid chain-length dependence of the interaction shows a discontinuity for helical polysaccharide segments shorter than 12 sugars and for fatty acids shorter than palmitate.

Thermodynamic and structural features of chloro-complex formation of bivalent transition metals in dimethylsulfoxide

Abstract: Heats of formation of complexes of the type MCl+ have been determined calorimetrically for M=Mn, Co, Ni, and Cu in dimethylsulfoxide (DMSO), at 25°C. Combined with the stability constants of the complexes they complete the thermodynamic characteristics of these systems. It appears that the complexes are formed in markedly endothermic reactions and owe their considerable stabilities to the large positive reaction entropies. The exceptionally large entropy of formation of the CuCl+ complex indicates its essentially pentacoordinate structure, CuCl(DMSO)4+, while the other complexes are octahedral, MCl(DMSO)5+, with a probable contribution of the outer-sphere ion-pair for CuCl+. The characteristic features of complex formation in dimethylsulfoxide, as compared with water, are discussed and ascribed to the relatively large molar entropy of this liquid.

Monolayers of triple long-chain salts on the concentrated sodium chloride solution

Abstract: The surface pressure–area (π–A) curves for monolayers of four kinds of cation-anion triple long-chain salts [dialkyldimethylammonium alkanesulfonates] on the aqueous solution of 4.4 M NaCl were measured at various temperatures by the Langmuir method. Some π–A curves of these salts showed two transition points. Judging from the apparent molar entropy change on the transition, the first was assigned to the transition from the expanded state (E phase) to the condensed state (C-I phase) and the second to the transition from the C-I phase to another condensed state (C-II phase). In this paper, another condensed phase (C-I′) was newly observed over a certain temperature range on the phase diagram, which is the intermediate phase between the C-I phase and the C-II phase. There exist two triple points on the phase diagram at which three phases (i.e., E, C-I, and C-I′, and C-I, C-I′, and C-II) coexist. From the apparent molar entropy change, limiting area, compressibility, and phase diagram, the orientation of (2–...

Thermal diffusion of dilute aqueous NH4Cl, Me4NCl, Et4NCl,n-Pr4NCl, andn-Bu4NCl solutions at 25°C

Abstract: The Soret effect (thermal diffusion) of dilute aqueous solutions of NH4Cl, Me4NCl, Et4NCl, n-Pr4NCl, and n-Bu4NCl has been investigated potentiometrically using the silver, silver chloride thermocell. The molar entropies (heats) of transport have been derived from the initial and final thermoelectric powers. The concentration dependence of the entropy of transport has been examined and the effect of the ionic size on the heat of transport is discussed. The molar entropy of tetrabutylammonium chloride exhibits a sharp minimum in the neighborhood of 0.002M, the reason of which is as yet unclear.

Thermodynamics-of precipitation of silver laurate from aqueous solution*

Abstract: The heat of precipitation of silver laurate was measured calorimetrically over the temperature range from 14 to 45°C, and the results compared with data derived from the dependence of silver laurate solubility on temperature. The standard enthalpy change was found to vary linearly with the thermodynamic temperature, whereas the standard entropy change was a linear function of the logarithm of the temperature. The slopes of both plots yielded the same value of the heat capacity change. Accordingly, the enthalpy of surfactant salts precipitation or dissolution cannot be obtained from the temperature dependency of solubility alone. The latter procedure is based on the assumption of negligible heat capacity change, which is not the case for precipitation reactions. The data on silver laurate also suggest that the heat capacity change does not vary much with temperature.

Gas adsorption on solids withGaussian micropore-size distributions

Abstract: This paper presents a theoretical description of gas adsorption on microporous solids withGaussian micropore-size distributions. This description comprises equations for the overall adsorption isotherm, the adsorption potential distribution, the differential molar enthalpy, and the differential molar entropy of adsorption. The truncatedGaussian micropore-size distribution is assumed to represent the structural heterogeneity of the micropores, whereas the adsorption potential distribution is used to characterize the energetic heterogeneity of these micropores.

Specific heat and related properties of some AIIBIVC and AIBIIIC semiconducting compounds between 2 and 300 K

Abstract: From specific heat measurements of the ternary semiconducting compounds ZnSiP2, ZnSiAs2, CdGeAs2, CuGaSe2, and CuInTe2 Debye characteristic temperatures and standard entropy values are calculated within the temperature range from 2 to 300 K. Aus Messungen der spezifischen Warmekapazitat der ternaren halbleitenden Verbindungen ZnSiP2, ZnSiAs2, CdGeP2, CuGaSe2, und CuInTe2 werden Debyetemperaturen und Standardentropien im Temperaturbereich von 2–300 K berechnet.

Effect of Carbon Dioxide on the Thermodynamic State of Water in Collagen

Abstract: Thermodynamic activities of polar sites of collagen in the presence of CO2 were observed by inverse gas chromatographic techniques using water as a probe. The interactions between collagen and the water probe were evaluated by determining the specific retention volume (Vg°) and partition coefficient (Kp) at 25°C, 3°C, and 35°C. Thermodynamic parameters were determined from these data. CO2 exhibited a significant effect on the water binding of collagen as shown by increased Vg° and Kp values as compared to N2- and He-treated collagen. The thermodynamic parameters of partial molar Gibb's free energy (ΔT°), partial molar enthalpy (ΔT°) and partial molar entropy (ΔT°) indicated CO2 significantly increased the average energy of water binding by collagen.