Showing papers on "Standard molar entropy published in 2007"

Thermodynamics and kinetics of cadmium adsorption onto oxidized granular activated carbon

Abstract: Cadmium sorption behavior of granular activated carbon oxidized with nitric acid was systematically studied by sets of the equilibrium and time-based experiments under various conditions. The cadmium adsorption capacity of oxidized granular activated carbon enlarged with an increase in pH, and reduced with an increase in ionic strength. Experimental data were evaluated to find out kinetic characteristics. Adsorption processes were found to follow pseudo-second order rate equation. Adsorption isotherms correlate well with the Langmuir isotherm model and the maximum sorption capacity of cadmium evaluated is 51.02 μmol/g. Thermodynamic parameters were calculated based on Van't Hoff equation. Equilibrium constant Kd was evaluated from Freundlich isotherm model constants, Langmuir isotherm model constants, and isotherms, respectively. The average change of standard adsorption heat ΔH0 was −25.29 kJ/mol. Negative ΔH0 and ΔG0 values indicate the adsorption process for cadmium onto the studied activated carbon is exothermic and spontaneous. The standard entropy ΔS 0 was also negative, which suggests a decrease in the freedom of the system.

Estimation of physicochemical properties of ionic liquid C6MIGaCl4 using surface tension and density.

Abstract: An ionic liquid (IL) C 6 MIGaCl 4 (l-methyl-3-hexylimidazolium chlorogallate) was prepared by directly mixing GaCl 3 and l-methyl-3-hexylimidazolium chloride with molar ratio of 1/1 under dry argon. The density and surface tension of the IL were determined in the temperature range of 283.15-338.15 K. The ionic volume and surface entropy of the IL were estimated by extrapolation, respectively. In terms of Glasser's theory, the standard molar entropy and lattice energy of the IL were estimated, respectively. By use of Kabo's method, the molar enthalpy of vaporization of the IL, Δ 1 g H m 0 (298 K), at 298 K was estimated. According to the interstice model, the thermal expansion coefficient of IL C 6 MIGaCl 4 , a, was calculated and in comparison with experimental value; their magnitude order is in good agreement.

Surface tension and density of 1 -methyl -3 -hexylimidazolium chloroindium

Abstract: The ionic liquid (IL) [C6mim][InCl4] (1-methyl-3-hexylimidazolium chloroindium) was prepared by directly mixing InCl3 and 1-methyl-3-hexylimidazolium chloride with a molar ratio of 1:1 under dry argon. The density and surface tension of the IL were determined in the temperature range of (283.15 to 338.15) K. The ionic volume and surface entropy of the IL were estimated by extrapolation, respectively. In terms of Glasser's theory, the standard molar entropy and lattice energy of the IL were estimated, respectively. Using Kabo's method and Rebelo's method, the molar enthalpy of vaporization of the IL, ΔlgHm0 (298 K), and ΔlgHm0 (Tb) at a hypothetical normal boiling point, Tb = 787 K, were estimated, respectively. According to the interstice model, the thermal expansion coefficient of IL [C6mim][InCl4] was estimated.

Thermal Modulation Voltammetry with Laser Heating at an Aqueous|Nitrobenzene Solution Microinterface: Determination of the Standard Entropy Changes of Transfer for Tetraalkylammonium Ions

Abstract: Thermal modulation voltammetry (TMV) with laser heating was successfully performed at an aqueous|nitrobenzene (NB) solution microinterface, by taking advantage of the fact that laser light with a wavelength of 325.0 nm is optically transparent to the aqueous solution but opaque to the NB solution. When the laser beam impinges upon the interface from the aqueous solution side, a temperature is raised around the interface through the thermal diffusion subsequent to the light-to-heat conversion following the optical absorption by the NB solution near the interface. Based on such a principle, we achieved a fluctuating temperature perturbation around the interface for TMV by periodically irradiating the interface with the laser beam. On the other hand, the fluctuating temperature perturbation has influence on currents for transfer of an ion across the interface to produce fluctuating currents synchronized with the perturbation through temperature coefficients of several variables concerning the transfer, such as the standard transfer potential and the diffusion coefficient of the ion. Consequently, TMV has the possibility of providing information about the standard entropy change of transfer corresponding to a temperature coefficient of the standard transfer potential and a temperature coefficient of the diffusion coefficient. In this work, the aqueous|NB solution interface of 30 microm in diameter was irradiated with the laser beam at 10 Hz, and the currents synchronized with the periodical irradiation were recorded as a function of the potential difference across the interface in order to construct a TM voltammogram. TM voltammograms were measured for transfer of tetramethylammonium, tetraethylammonium, tetrapropylammonium, and tetra-n-butylammonium ions from the aqueous solution to the NB solution, and the standard entropy change of transfer was determined for each ion, according to an analytical procedure based on a mathematical expression of the TM voltammogram. Comparison of the values obtained in this work with the literature values has proved that TMV with laser heating is available for the determination of the standard entropy change of transfer for an ion.

Heat capacity of synthetic hydrous Mg-cordierite at low temperatures: Thermodynamic properties and the behavior of the H2O molecule in selected hydrous micro and nanoporous silicates

Abstract: The heat capacity, CP, of a synthetic hydrous cordierite of composition Mg1.97Al3.94Si5.06O18·0.625H2O was measured for the Þ rst time using precise adiabatic calorimetry in the temperature range from 6 to 300 K. Hydrous Mg-cordierite was obtained by hydrothermal treatment of anhydrous Mg-cordierite (Paukov et al. 2006) at 4 kbar and 600 °C for 24 hours. The synthetic product was characterized using X-ray diffraction and powder IR spectroscopy. Rietveld reÞ nement gives a = 17.060(2) A, b = 9.721(1) A, and c = 9.338(1) A with V = 1548.7(3) A 3 and ∆ = 0.25, and the IR spectrum shows only the presence of Class I-Type I H2O in the channel cavities. Small CP anomalies were observed at 272.98 ±0.03 K and 239.43 ±0.13 K, which are thought to be related to very small amounts of H2O occurring in tiny s uid inclusions and to surface H2O, respectively. From the heat-capacity data on hydrous Mg-cordierite, various thermodynamic functions were calculated and are presented in table form. The calculated partial molar entropy for one mole of H2O in hydrous Mg-cordierite at 298.15 K and 1 bar is 80.5 J/(mol·K). The partial molar volume for H2O in hydrous Mg-cordierite at 298 K and 1 bar is zero. The CP results, together with published heat-capacity data on three different zeolites, permit a comparison and analysis of their heat-capacity behavior. The heat-capacity behavior of H2O molecules in zeolites is more similar to that of ice at T 300 K, the heat capacity for H2O is the smallest in steam with values increasing in hydrous beryl and cordierite, to H2O in various zeolites, and Þ nally to liquid H2O. This behavior may res ect the nature of the hydrogen bonding and the energies of internal H2O stretching modes, which decrease in energy with increasing hydrogen-bonding strength in the various systems.

Low-temperature heat capacities of MgAl 2 O 4 and spinels of the MgCr 2 O 4 -MgAl 2 O 4 solid solution

Abstract: We present results from low-temperature heat capacity measurements of spinels along the solid solution between MgAl2O4 and MgCr2O4. The data also include new low-temperature heat capacity measurements for MgAl2O4 spinel. Heat capacities were measured between 1.5 and 300 K, and thermochemical functions were derived from the results. No heat capacity anomaly was observed for MgAl2O4 spinel; however, we observe a low-temperature heat capacity anomaly for Cr-bearing spinels at temperatures below 15 K. From our data we calculate standard entropies (298.15 K) for Mg(Cr,Al)2O4 spinels. We suggest a standard entropy for MgAl2O4 of 80.9 ± 0.6 J mol−1 K−1. For the solid solution between MgAl2O4 and MgCr2O4, we observe a linear increase of the standard entropies from 80.9 J mol−1 K−1 for MgAl2O4 to 118.3 J mol−1 K−1 for MgCr2O4.

Heat-pulse calorimetry measurements on natural chlorite-group minerals

Abstract: Low- and high-temperature heat capacities of five natural chlorite-group samples were measured using the heat-capacity option of the Physical Properties Measurement System (Quantum Design), which is based on the principles of heat-pulse calorimetry, and by differential scanning calorimetry. Comprehensive chemical analyses were performed on these samples by electron microprobe analysis, by inductively coupled plasma mass spectrometry, and by Karl-Fischer titration (for H2O). The natural chlorites span a range in X-Fe from 0.052 to 0.885 with increasing Al-content due to the Tschermak substitution with increasing X-Fe. The measured heat capacities were extrapolated to the end-member compositions of chamosite and clinochlore. Integration of heat-capacity data yields the calorimetric standard entropies of chamosite (Fe5Al)[Si3AlO10](OH)(8) and clinochlore (Mg5Al)[Si3AlO10](OH)(8), with values of 572.0 +/- 0.2 and 425.6 +/- 0.4 J/(mol-K), respectively. The C-p-polynomial for end-member chamosite is C-p = 1151.7 - 8.4564 x 10(3)-T-0.5 - 13.206 x 10(6)-T-2 + 15.233 x 10(8).T-3 [J/(mol-K)], valid in the temperature range of 298.15-900 K, and that for end-member clinochlore is C-p = 1160.5 - 9.9819 x 10(3)-T-0.5 - 5.9534 x 10(6).T-2 + 3.8677 x 10(8)-T-3 [J/(mol-K)], valid in the temperature range of 298.15-1000 K. The Fe-rich chlorites exhibit an asymmetric distribution of the excess heat capacity in a plot of C-p(ex) vs. T, with a maximum at about 52 K. By analogy to annite, we interpret this peak to represent the magnetic ordering temperature. Based on our standard entropy value for chamosite, the enthalpy of formation of berthierine (Fe2.5Al0.5)[Si1.5Al0.5O5Y](OH)(4) was estimated as -3570.30 kJ/mol using a reported onset temperature of 70 degrees C at 16 MPa for the berthierine-chamosite polymorphic transition.

Inclusion Complex Formation of Thiacalix[4]arene and Xe in Aqueous Solution Studied by Hyperpolarized 129Xe NMR

Abstract: The inclusion complex formation of 4-sulfothiacalix[4]arene sodium salt (STCAS) and Xe has been investigated by using hyperpolarized 129Xe NMR spectroscopy. Our new continuous-flow type hyperpolarizing system has advantageous capabilities that can supply hyperpolarized gases continuously and directly to a sample solution in a NMR tube. Consequently saturated Xe concentration in the aqueous solution of STCAS is maintained during the NMR experiment, and 129Xe NMR spectra can be obtained in remarkably short time. STCAS concentration dependence of 129Xe chemical shift has been analyzed in an elaborated way by a computer method as well as a simple graphic method that we have proposed. The association constant K:13.6±0.8 M−1 at 25 °C was obtained, and further analysis of the temperature dependence has successfully given thermodynamic parameters of enthalpy (ΔH) and entropy (ΔS) for the inclusion complex formation: ΔH = −11.9±1.9 kJ mol−1 and ΔS = −17.4±5.8 JK−1 mol−1. The energetic aspects of complex formation are discussed from the size effect and from the molecular theory of standard entropy, and a release of definite number of water molecules from STCAS cavity is suggested in the inclusion complex formation with Xe.

Experimental Study of the Chemical Equilibria in the Liquid-Phase Dehydration of 1-Pentanol to Di-n-pentyl Ether

Abstract: The thermodynamic equilibrium of the liquid-phase bimolecular dehydration of 1-pentanol to di-n-pentyl ether (DNPE) and water was studied in the temperature range of 423−463 K over Amberlyst 70. Furthermore, the equilibrium position of two side reactions could be followed, DNPE decomposition to 1-pentanol and 1-pentene and isomerization of 1-pentene to 2-pentene. The etherification reaction proved to be slightly exothermic, with an enthalpy change of reaction at 298.15 K of −(3.8 ± 0.6) kJ mol-1. From this value, the standard formation enthalpy and molar entropy of DNPE were computed to be −(421.1 ± 1.2) kJ mol-1 and 473.71 J (K·mol)-1, respectively. The enthalpy changes of the reaction of DNPE decomposition to 1-pentene and 1-pentanol and 1-pentene isomerization to 2-pentene were 63.4 ± 0.9 and −19.7 ± 2.1 kJ mol-1, respectively.

Solvent release upon ion association from entropy data. II

Abstract: When a cation and an anion associate, the charge on the product is lower than that on the individual ions and solvent is released from their solvation shells to the bulk solvent. This release occurs when the associate is a solvent-shared or contact ion pair or an inner-type complex. The measurable molar entropy change involved is considered to be made up of four contributions: translational, rotational, electrostatic, and desolvation entropies. The former three can be calculated from the properties of the ions and solvents involved; hence, the fourth is obtained by difference. The release of solvent molecules from the crystalline frozen solvent to the liquid on melting is analogous to the solvent release from translational immobilization in the solvation shells of the ions. The molar entropy of melting of the solvent is used to estimate the amount of solvent released in the association process.

Thermodynamic functions of elements and compounds: Entropies of inorganic substances

Abstract: The standard entropies of solid elements and inorganic compounds have been related to atomic or molar volumes after grouping the substances according to the periodic classification, compound type and crystal structure. It is shown that, within each sub-group, standard entropy and molar volume are related by the expression S = aVn. For elements and simple compounds, the entropy increase between 298° K and the melting point is related parabolically to the respective temperature rise. The entropy increase for complex compounds is less than that for simple compounds and is also dependent on type of compound. Entropy of fusion is related to temperature in the same manner. It is indicated that the entropy of formation of solid products from solid reactants is directly proportional to the volume change during the reaction.

The heat capacity and standard thermodynamic functions of Ni 0.5 Zr 2 (PO 4 ) 3 phosphate over the temperature range from T→0 to 664 K

Abstract: The temperature dependence of the heat capacity of crystalline nickel zirconium phosphate C°p = f(T) was measured over the temperature range 6–664 K. The experimental data obtained were used to calculate the standard thermodynamic functions of Ni0.5Zr2(PO4)3 from T → 0 to 664 K. The standard entropy of phosphate formation from simple substances at 298.15 K was calculated from the absolute entropy of the compound. The data on the low-temperature heat capacity were used to determine the fractal dimension of Ni0.5Zr2(PO4)3 over the temperature range 30–50 K. Conclusions concerning the heterodynamic characteristics of the structure of Ni0.5Zr2(PO4)3 were drawn.

Effects of Particle Size on Properties of Chemical Reaction Thermodynamics of Nanosystems

Abstract: In order to study size dependence of the thermodynamic properties of chemical reaction, nanoparticles of diamond were simulated by use of spherical C clusters, the properties of chemical reaction of diamond nanoparticles with different sizes and O_2 were calculated by quantum chemistry method. The results showed that the particle size had obvious effects on the molar standard entropy of reaction, the molar standard enthalpy of reaction, the molar standard Gibbs free energy, and the standard equilibrium constant in heterogeneous reactions; the molar standard entropy of reaction, the molar standard enthalpy of reaction, and the molar standard Gibbs free energy decreased and the standard equilibrium constant increased with the particle diameters of reactants decreasing. These regularities were consistent with experimental results.

Thermodynamics and Kinetics of Chiral Separations with β‐Cyclodextrin Stationary Phase: II. Effect of Temperature and Pressure

Abstract: In this study, a series of coumarin‐based compounds is separated using a β‐cyclodextrin stationary phase with a polar‐organic mobile phase. Temperature and pressure are varied in order to observe the effects and determine important thermodynamic and kinetic parameters. Increasing the temperature decreases the retention and chiral selectivity, but increases the mass transfer rates for all chiral compounds. Increasing the pressure decreases the retention, but does not significantly affect the chiral selectivity. Van't Hoff plots of the natural logarithm of retention factor versus inverse temperature are linear with positive slopes, indicating an enthalpically favorable transfer from mobile to stationary phase. The second eluted enantiomer has a more negative change in molar enthalpy than the first, suggesting an enthalpically more favorable transfer. For all compounds, both the differential change in molar enthalpy and the differential change in molar entropy between the two enantiomers are negativ...

Standard molar enthalpies of formation and sublimation of n-phenylphthalimide

Abstract: The standard (p 0=0.1 MPa) molar enthalpy of formation, Δf H 0 m, for crystalline N-phenylphthalimide was derived from its standard molar enthalpy of combustion, in oxygen, at the temperature 298.15 K, measured by static bomb-combustion calorimetry, as –206.0±3.4 kJ mol–1. The standard molar enthalpy of sublimation, Δg cr H 0 m , at T=298.15 K, was derived, from high temperature Calvet microcalorimetry, as 121.3±1.0 kJ mol–1. The derived standard molar enthalpy of formation, in the gaseous state, is analysed in terms of enthalpic increments and interpreted in terms of molecular structure.

Phase equilibria and thermodynamic properties of the system Tl-TlCl-Se

Abstract: Phase equilibria in the system Tl-Se-Cl were studied in the region Tl-TlCl-Se by DTA, X-ray powder diffraction, emf measurements concentration circuits (−) Tl/glycerol + KCl + TlCl/(Tl-Se-Ce) (+), and microhardness measurements. Several vertical sections, an isothermal section at 400 K, and the liquidus-surface projection were constructed. The primary crystallization regions and homogeneity regions of phases were determined, including the α phase of variable composition based on Tl5Se2Cl, the only ternary compound of the system. The types and coordinates of invariant and monovariant equilibria on the T-x-y diagram were determined. From the results of emf measurements, the standard thermodynamic functions of formation and the standard entropy were calculated for the compound Tl5Se2Cl.

Heat capacity and heat content of BiNb5O14

Abstract: The heat capacity and the heat content of bismuth niobate BiNb5O14 were measured by the relaxation time method, DSC and drop method, respectively. The temperature dependence of heat capacity in the form C pm=455.84+0.06016T–7.7342·106/T 2 (J K–1 mol–1) was derived by the least squares method from the experimental data. Furthermore, the standard molar entropy at 298.15 K S m=397.17 J K–1 mol–1 was derived from the low temperature heat capacity measurement.

Standard Gibbs energy of formation of Pb2Ru2O6.5

Abstract: Lead ruthenate is used as a bifunctional electrocatalyst for both oxygen evolution and reduction and as a conducting component in thick-film resistors. It also has potential applications in supercapacitors and solid oxide fuel cells. However, thermodynamic properties of the compound have not been reported in the literature. The standard Gibbs energy of formation has now been determined in the temperature range from 873 to 1123 K using a solid-state cell incorporating yttria-stabilized zirconia (YSZ) as the electrolyte, a mixture of $PbO + Pb_2Ru_2O_{6.5}+ Ru$ as the measuring electrode, and $Ru + RuO_2$ as the reference. The design of the measuring electrode is based on a study of phase relations in the ternary system Pb–Ru–O at 1123 K. For the reaction, $2PbO (ortho) + 2RuO_2 (rut) + 1/4O_2(g) = Pb_2Ru_2O_{6.5}$(pyro) $\Delta G_r^o /J mol^{−1} (\pm524)$ = −80224+75.763(T/K) − 5.873(T/K)ln (T/K) , the standard enthalpy of formation and standard entropy at 298.15 K are estimated from the high-temperature measurements. An oxygen potential diagram for the system Pb–Ru–O is composed based on data obtained in this study and auxiliary information from the literature.

The thermodynamic properties of crystalline Sr0.5Zr2(PO4)3 phosphate from T → 0 to 665 K

Abstract: The temperature dependence of the heat capacity of crystalline Sr0.5Zr2(PO4)3 phosphate was studied by precision adiabatic vacuum and dynamic scanning calorimetry over the temperature range 7–665 K. The low-temperature dependence of the heat capacity was analyzed using the Debye theory of the heat capacity of solids and its multifractal generalization, which allowed conclusions to be drawn about the heterodynamic characteristics of the structure. The experimental data obtained were used to calculate the standard thermodynamic functions of Sr0.5Zr2(PO4)3 from T → 0 to 665 K. The standard absolute entropy of Sr0.5Zr2(PO4)3 was in turn used to calculate the standard entropy of its formation from simple substances at 298.15 K.