Showing papers on "Standard molar entropy published in 2003"

Standard Absolute Entropy, , Values from Volume or Density. 1. Inorganic Materials

Abstract: Standard absolute entropies of many inorganic materials are unknown; this precludes a full understanding of their thermodynamic stabilities. It is shown here that formula unit volume, Vm, can be employed for the general estimation of standard entropy, , values for inorganic materials of varying stoichiometry (including minerals), through a simple linear correlation between entropy and molar volume. Vm can be obtained from a number of possible sources, or alternatively density, ρ, may be used as the source of data. The approach can also be extended to estimate entropies for hypothesized materials. The regression lines pass close to the origin, with the following formulas: For inorganic ionic salts, /J K-1 mol-1 = 1360 (Vm/nm3 formula unit-1) + 15 or = 2.258 [M/(ρ/g cm-3)] + 15. For ionic hydrates, /J K-1 mol-1 = 1579 (Vm/nm3 formula unit-1) + 6 or = 2.621 [M/(ρ/g cm-3)] + 6. For minerals, /J K-1 mol-1 = 1262 (Vm/nm3 formula unit-1) + 13 or = 2.095 [M/(ρ/g cm-3)] + 13. Coupled with our published procedures,...

The thermodynamics of tetrataenite and awaruite: A review of the Fe-Ni phase diagram

Abstract: There are two well-known ordered ferromagnetic intermetallic compounds in the iron-nickel system: tetrataenite, FeNi, and awaruite, FeNi3. Their thermodynamic properties are established from the various stable and metastable equilibria in which they are involved, and a review to make this data accessible is appropriate. The Fe-Ni phase diagram shows a paramagnetic face-centered cubic phase (gamma) with well-measured properties over the entire composition range from 1184 to 1662 K. Its properties can be extrapolated to lower temperatures, and known stable and metastable equilibria are used to establish models for the thermodynamic properties of the ferromagnetic alpha phase, a high-temperature paramagnetic alpha phase, a paramagnetic gamma-ordered Fe3Ni phase, the ferromagnetic disordered gamma phase, and both ordered ferromagnetic gamma phases, tetrataenite, FeNi, and awaruite, FeNi3. The overestimate of Chuang et al. for the entropy of ordering in awaruite is corrected. The standard enthalpies at 298.15 K of tetrataenite (0.5 FeNi) and awaruite (0.25 FeNi3) are −1170 and −3560±1000 J mol−1. The corresponding standard entropy values are 35.7 and 33.3±3 J mol−1 K−1. All the second-order transitions are accurately modeled and the full phase diagram is calculated. The spinodal regions and metastable equilibria responsible for the complex behavior on cooling of alloys with mole fractions of nickel between 0.26 and 0.40 are described in detail.

Refinement of thermodynamic data for LaMnO3

Abstract: The standard Gibbs energy of formation of LaMnO3 has been measured in the temperature range from 900 to 1400 K using a solid-state cell incorporating a buffer electrode. The oxygen potential corresponding to the three-phase mixture MnO + La2O3 + LaMnO3 has been measured using pure oxygen gas at 0.1 MPa as the reference electrode, and yttria-stabilized zirconia as the solid electrolyte. The buffer electrode prevented polarization of the three-phase electrode and ensured accurate data. The measured oxygen chemical potential corresponding to the decomposition of LaMnO3−δ to MnO, La2O3 and O2 gas is in fair agreement (±6 kJ mol−1) with most data available in the literature and can be represented by the equation,ΔμO2/J mol−1 (±520) = −583160 + 170.55 (T/K)Combining this with available information on oxygen potential variation with the non-stoichiometric parameter δ, the standard Gibbs free energy of formation of LaMnO3 from MnO, La2O3 and O2 was evaluated. The correction for non-stoichiometry was ∼1.6(±0.7) kJ mol−1. The heat capacity of LaMnO3 has been measured by a differential scanning calorimeter from 400 to 1060 K. Information on low-temperature heat capacity available in the literature was joined smoothly with the high-temperature data to evaluate the standard entropy of LaMnO3 at 298.15 K as 116.68 J mol−1 K−1. The “third-law” analysis of the Gibbs energy values obtained in this study yields a value of −155.93 (±0.8) kJ mol−1 for the standard enthalpy of formation of LaMnO3 from MnO, La2O3 and O2 at 298.15 K. This value provides a critical test of calorimetric data on enthalpy of formation of LaMnO3. A consistent set of thermodynamic data for LaMnO3 is presented from 298.15 to 1400 K based on the results obtained in this study and other supporting information in the literature.

Thermodynamic properties of hercynite (FeAl2O4) based on adiabatic calorimetry at low temperatures

Abstract: The low-temperature heat capacity of hercynite (FeAl2O4) was measured between 3 and 400 K, and thermochemical functions were derived from the results. The measured heat-capacity curve shows a small lambda-shaped anomaly peaking at around 13 K. From our data, we suggest a standard entropy for hercynite at 298.15 K of 113.9 ± 0.2 J/(mol·K), which is some 7.6 J/(mol·K) higher than reported previously by a calorimetric study that missed the entropy contributions of the lowtemperature anomaly.

Determination of the Entropy of Ion Transfer between Two Immiscible Liquids Using the Water|Oil|Water Thermocouple

Abstract: A nonisothermal galvanic cell comprising two interfaces between two immiscible electrolyte solutions has been employed to determine the standard entropy ( ) of ion transfer at the nitrobenzene (NB)|water (W) interface. Under the conditions that only one ion (i) can partition between the NB|W interface, the nonisothermal emf has been measured. A nonequilibrium thermodynamic treatment has shown that the peak value (E0) of the nonisothermal emf, being usually observed within 1 min, is related to for ion i. However, E0 has also been shown, both experimentally and theoretically, to be influenced by thermal diffusion potentials arising in the bulk phases. Nevertheless, the contributions from the thermal diffusion potentials can be corrected for if the parameters for the ionic heats of transport are available, or they can be minimized by using adequate supporting electrolytes. Thus, accurate values of have been determined for various cations and anions. The determined values of for relatively hydrophobic cations...

Temperature dependence of dielectric relaxation of rigid polar molecules acetophenone, pyridine and their mixtures in dilute solutions of benzene

Abstract: The dielectric absorption studies of acetophenone, pyridine and their binary mixtures, both consisting of rigid molecules, have been studied at 8.93 GHz in the dilute solutions of benzene at different temperatures. The relaxation times, dipole moments, thermodynamical parameters, viz. free energy, enthalpy and entropy of activation have been calculated from the dielectric data. The relaxation time (1: 11) of the single component agrees well with literature values. The experimental values of relaxation time (1: 11) of the dipolar mixture have been compared with the theoretical values obtained by employing different methods. The non-linear behaviour of ~ 2 versus mole fraction is explained on the basis of solute­ solute molecular association between these two-polar rigid molecules. The values of the molar entropy for the relaxation process indicate that , the cooperative orientation of the molecules in the single component system is retained in the mixture also.

Excess partial molar entropy of alkane-mono-ols in aqueous solutions at 25°C

Abstract: In the preceding paper, we reported the values of model-free chemical potentials for aqueous methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and 1-hexanol at 25°C over the entire compositiona...

Absorbed heat and heat of formation of dried microbial biomassstudies on the thermodynamics of microbial growth

Abstract: As represented by equations in which there is a term representing the biomass, the thermodynamics of biological growth processes is difficult to study without knowing the thermodynamic properties of cellular structural fabric. Measurement of the heat capacity data required to determine the standard entropy, S298 15

High temperature 93Nb NMR and Raman spectroscopic investigation of the structure and dynamics of solid and liquid NbCl5-alkali chloride solutions

Abstract: Pure liquid niobium chloride and solid and liquid NbCl5-alkali chloride solutions were for the first time studied by 93Nb NMR. Chemical shift (δ) and line width (Δν1/2) measurements were made by using a laboratory made probe head for experiments at elevated temperatures up to 650 °C. In the case of NbCl5-(LiCl/KCl)eut, where the salt mixture was not opaque, also Raman spectra could be recorded. For pure liquid NbCl5 the monomer–dimer equilibrium could be investigated. In the temperature range 200 °C to ca. 500 °C from the temperature dependence of both δ and Δν1/2 the equilibrium constant and the standard entropy and enthalpy for this reaction have been obtained. Binary NbCl5–CsCl and NbCl5–NaCl salt melts and solutions of NbCl5 in solid and liquid eutectic mixtures were investigated by 93Nb NMR. For some mixtures where the phase behaviour was only partially known, additional differential thermoanalysis (DTA) measurements of the phase diagrams have been performed. By 93Nb NMR a distinctly different behaviour of CsCl and NaCl containing melts is observed, where the the CsCl melts show relative broad resonance lines and a large negative chemical shift, whereas the NaCl melts reveal typically narrow lines and positive shifts. The broad lines are discussed with respect to the self-reduction reaction Nb5+ → Nb4+. In the high temperature solid phases of both NaCl and CsCl containing mixtures unusually narrow lines are explained by a fast ionic hopping process in these materials. The stability of oxy complexes in different salt matrices is also discussed. Finally, the observed temperature dependence of the 93Nb chemical shift (ca. 0.1 ppm K−1) in different salt mixtures is found to be in qualitative agreement with a theoretical estimate, which considers the Nb–Cl distance variation with temperature.

Thermodynamic and dilatometric properties of the dimerized phase of a C60 fullerene

Abstract: This paper reports on the results of complex investigations into the structural, thermodynamic, and dilatometric properties of the C60 dimerized phase prepared under compression of a C60 fullerite at a pressure up to 8 GPa and a temperature of 290 K. It is demonstrated that the dimerized phase has a face-centered cubic structure with a lattice parameter a=14.02±0.05 A. The dimeric structure of the studied sample is confirmed by x-ray diffraction analysis. According to the dilatometric data, the volume jump observed in the vicinity of the orientational transition for the dimerized phase is estimated to be approximately 30 times less than that for the C60 fullerite. The temperature dependence of the heat capacity of the (C60)2 crystalline dimer is examined using precision adiabatic vacuum calorimetry under normal pressure in the temperature range from T → 0 K to 340 K. The results obtained are used in the calculations of thermodynamic functions, namely, the heat capacity C p 0 (T), the enthalpy H 0(T)-H 0(0), the entropy S 0(T), and the Gibbs function G 0(T)-H 0(0). The fractal dimension D is determined as a function of the heat capacity. The standard entropy of the formation of the (C60)2 crystalline dimer from a simple compound (graphite) at T=298.15 K and normal pressure is calculated.

Thermodynamic and adsorption properties of semiinterpenetrating polymer networks based on polybenzimidazoles and polyaminoimide resin

Abstract: Thermodynamic characteristics of adsorption of organic compounds on semiinterpenetrating networks based on polybenzimidazoles and polyaminoimide resin with different compositions were studied at small coverages using inverse gas chromatography. The following characteristics were determined: adsorption equilibrium constants (specific retention volumes) of substances of different classes (n-alkanes, aromatic hydrocarbons, ethers, ketones, alcohols, and nitrogen- and halogen-containing compounds), appropriate changes in differential molar internal energy and Helmholtz potential, and changes in standard molar entropy of the sorbates. The contributions of the molecular fragments to the heat of adsorption were calculated. The adsorption properties of the semiinterpenetrating networks based on polybenzimidazoles and polyaminoimide resin differ from those of the starting polymeric materials and their physical mixtures with the similar composition. Unlike graphitized thermal carbon black (nonspecific adsorbent), the network and starting materials manifest the specific properties (electron-donating and electron-accepting). The difference in the thermodynamic characteristics of adsorption on the semiinterpenetrating polymeric networks with different compositions is determined by the size and geometry of interphase regions.

Irreversible thermodynamics of reversible polymerization reactions

Abstract: Based on the theory of irreversible thermodynamics explicit expressions are derived for the entropy production during reversible polymerization of bifunctional linear polymers whose initial molecular weight distribution can be chosen arbitrarily. The time-dependent course of the entropy production is explicitly calculated for two cases where the reaction starts (a) from monomer and (b) from monodisperse polymer molecules. In both cases we treat the system to be ideal and the time dependant change of the number of molecules is described by a kinetic approach using two kinetic constants for the forward and backward reactions, respectively. During reversible polymerization the entropy production σred is a monotonously decreasing function approaching zero when the system reaches the equilibrium molecular weight distribution with σred being positive in accordance with the second law of thermodynamics. In case of starting reaction from monodisperse polymer molecules under constraint that the number average chai...

Study on Thermochemistry of Hydrated Potassium Monoborate

Abstract: Hydrated potassium monoborate(KBO 2 ·4/3H 2 O)was obtained from an aqueous solutio n in a mole ratio of K 2 O∶B 2 O 3 =2∶1and characterized by powder X-ray diffraction(XRD),infrared spectroscopy(FT-IR)and Raman spectroscopy.The enthalpy of solut ion of hydrated potassium monoborate,KBO 2 ·4/3H 2 O,in approximately1mol·dm -3 aqueous hydrochloric acid was determined.Together with the previously determined enthalpies of so-lution of H 3 BO 3 in approximately 1mol·dm -3 HCl (aq),and of KCl in aqueous(hydrochloric acid +boric acid),the standard molar enthalpy of forma tion of -(1411.11±0.84)kJ·mol -1 for KBO 2 ·4/3H 2 O was obtained from the standard molar enthalpies of formation of KCl (s),H 3 BO 3 (s),and H 2 O(l).The standard molar entropy of formation of -422.94J ·K -1 ·mol -1 and standard molar entropy of 163.47J·K -1 ·mol -1 for KBO 2 ·4/3H 2 O were calculated from the thermodynamic relations.A group contribution method is applicable to KBO 2 ·4/3H 2 O.

The thermodynamic characteristics of lithium uranoborate

Abstract: The standard enthalpy of formation of crystalline LiBUO 5 at 298.15 K was determined by reaction calorimetry. The heat capacity of the compound was studied by adiabatic vacuum calorimetry in the temperature range 7-300 K.The experimental data were used to calculate its thermodynamic functions (the standard entropy and the Gibbs energy of formation at 298.15 K). The standard thermodynamic functions of reactions used to synthesize lithium uranoborate were calculated and analyzed.

Studies on the Correlativities of Partition Function with Standard Entropy and Hydrated Enthalpy of Cations

Abstract: Based on the relationship between partition function and entropy in statistical thermodynamics for a distinguishable particle system, the atomic weight (A_(r,i)) and electronic shell number(n_i) of ground state atom i has an excellent correlativity with the standard entropies \{[S~0_m/(J·mol~(-1)·K~(-1))]\} of 70 cations in solid compounds: S~0_m=(-0.51)+(3.59)·((1.5\}ln A_(r,i))~(1.4)-\{0.31(ln\} n_i)~2, R=(0.999 6.) Based on the relationship between enthalpy and partition function for an indistinguishable particle system, the linear regression equation between ground state energies (e_i) and hydrated enthalpies[-Δ_hH_m/(kJ·mol~(-1))] of 51 metal ions is drawn up: -Δ_hH_m=46.93+525.49e_i, R=(0.992 0). The calculated values of S~0_m, (Δ_hH_m) basically tally with the experiment values.

Thermodynamics of Copper Uranogermanate

Abstract: The standard enthalpy of formation of crystalline copper uranogermanate at 298.15 K and the standard enthalpies of dehydration of its crystal hydrates were determined by reaction calorimetry. The heat capacity of Cu(HGeUO6)2·6H2O was measured by adiabatic vacuum calorimetry in the range 80-300 K, and the thermodynamic functions of this compound, as well as the standard entropy and Gibbs energy of its formation at 298.15 K, were calculated. The standard thermodynamic functions of the reactions of synthesis and thermal decomposition of copper uranogermanate were calculated and discussed.