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Showing papers on "Standard molar entropy published in 2000"


Journal ArticleDOI
TL;DR: In this paper, the beads of hybrid inorganic ion exchanger: styrene supported zirconium (IV) tungstophosphate for a pesticide phosphamidon at 30, 45 and 60°C.

128 citations


Journal ArticleDOI
TL;DR: This work presents a simple statistical-thermodynamic scheme for calculating the adsorption entropy, including its resolution into translational and rotational contributions, using the known distance-orientation dependent binding (adsorption) potential.

96 citations


Journal ArticleDOI
TL;DR: In this paper, a double-twin microcalorimeter is used to measure the partial molar enthalpy and the chemical potential of the water in a lipid headgroup.
Abstract: We present a novel method for monitoring isothermal lipid hydration using a sorption microcalorimeter. A measuring cell of the double-twin calorimeter consists of two vessels connected by a stainless steel tube. The upper vessel contains pure water, and the bottom vessel is loaded with the lipid sample. This calorimeter allows for simultaneous measurement of the partial molar enthalpy and the chemical potential (or the partial molar free energy) of the water. The versatility of the method is demonstrated by studies of the hydration of the phospholipids dipalmitoyl phosphatyl choline (DPPC), dimyristoyl phosphatidyl choline (DMPC), and dilauroyl phosphatidyle choline (DLPC) at 25 and 27 C. The measurements provide a relation between water content and water chemical potential, which, in these lamellar systems, is often recast as a force-distance relation and has been called the hydration force. Through the simultaneously monitored calorimetric values, the partial molar enthalpy of water is also obtained. The method consequently provides a rather unique combination of information on both partial molar enthalpy and partial molar free energy and thus also the partial molar entropy of the process. We find that the incorporation of the first three to four water molecules per lipid is exothermic. These water molecules presumably interact directly with oxygen atoms on the phosphate of the lipid headgroup. When the first waters have been added, the remaining ones are incorporated endothermically. This applies to the water molecules taken up both in the gel phase and in the liquid crystalline state. We also observe that the sorption process triggers a first-order phase change from a gel (L') to a liquid crystalline (L) phase. For DLPC, this occurs at 25 C at a relative humidity of 0.79 with an endothermic transition enthalpy of 42 ± 2 kJ/mol (DLPC) and, for DMPC, at 27 C at 0.93 relative humidity with H = 56 ± 5 kJ/mol (DMPC). We use a previously established model to quantitatively interpret these phase transitions. Furthermore, the observed endothermic nature of the sorption process above three to four waters per lipid is fully consistent with the suggestion that the negative free energy of the sorption (swelling) is due to increased thermal excitations and thus a positive entropy. It is more problematic to reconcile the data with models proposing structuring effects in the water as the main cause of the swelling. (Less)

74 citations


Journal ArticleDOI
TL;DR: In this paper, the heat capacity of synthetic eskolaite, Cr2O3, and of the synthetic spinels Magnesiochromite, MgCr2O4, and chromite, FeCr2 O4 were measured from 1.5 K to 340 K, which indicated the transition to antiferromagnetic long-range order.
Abstract: The heat capacity of synthetic eskolaite, Cr2O3, and of the synthetic spinels magnesiochromite, MgCr2O4, and chromite, FeCr2O4 were measured from 1.5 K to 340 K. For MgCr2O4, a substantial magnetic contribution to the entropy is revealed by a sharp peak in the heat capacity curve at 12.55 ± 0.05 K, which indicates the transition to antiferromagnetic long-range order. Integration of the heat capacity curve yields a value of 118.3 ± 1.2 J/(mol·K) for the standard entropy at 298.15 K, which is in excellent agreement with that calculated from phase equilibria studies on the reaction MgCr2O4 + SiO2 = Cr2O3 + MgSiO3. The new calorimetric results for Cr2O3 indicate a standard entropy at 298.15 K of 82.8 ± 0.8 J/(mol·K). The measurements for FeCr2O4 show three distinct heat capacity anomalies, one of which (peaking at 36.5 ± 0.2 K) was missed by previous low temperature heat capacity measurements, which only extend down to 53 K. Integration of the heat capacity curve yields a value for the standard entropy at 298.15 K of 152.2 ± 3.0 J/(mol·K) for FeCr2O4, some 6 J/ (mol·K) greater than the previous calorimetric value. These low-temperature heat capacity data were combined with high-temperature heat content measurements from the literature to derive heat capacity equations for all three phases to 1800 K. The resulting heat capacity equations were then used to extract revised recommended values of the standard enthalpies of formation and entropies of MgCr2O4 and Cr2O3 from phase equilibrium data. For FeCr2O4, the phase equilibrium data are of dubious accuracy, the enthalpy of formation is only approximate.

72 citations


Journal ArticleDOI
TL;DR: In this article, the association of acid orange 7 and cetylpyridinium chloride (S) was studied at 15, 25, 35 and 45°C in the presence of 0, 0.05 and 0.1 mol/kg NaCl, by potentiometric titration, using a surfactant cation sensitive membrane electrode.

49 citations


Journal ArticleDOI
TL;DR: In this paper, the adsorption thermodynamics of oxamyl on fly ash at 10°C, 25°C and 50°C have been studied via the relevant adorption isotherms, Freundlich constants (KF and 1/n), distribution coefficient (Kd), and other thermodynamic parameters.
Abstract: The adsorption thermodynamics of oxamyl on fly ash at 10°C, 25°C and 50°C have been studied via the relevant adsorption isotherms, Freundlich constants (KF and 1/n), distribution coefficient (Kd) and other thermodynamic parameters. The data were well fitted by the Freundlicdhequation (r2 > 0.98) and yielded S-shaped isotherms at all the temperatures studied. Thermodynamic parameters such as the thermodynamic equilibrium constant (K0), the standard free energy change (ΔG0), the standard enthalpy change (ΔH0) and the standard entropy change (ΔS0) have been calculated as a means of predicting the nature of the adsorption process.

45 citations


Journal ArticleDOI
TL;DR: In this investigation, respective thermodynamic parameters of heats of formation, standard entropy and specific heat capacity at constant pressure for PCDDs, PCDFs, Co-PCB and PCBs as well as polychlorinated-benzenes and poly chlorinated-phenols have been evaluated by quantum chemical calculation using a semi-empirical molecular orbital method with the PM3 Hamiltonian and statistical thermodynamic correlation.

43 citations


Journal ArticleDOI
TL;DR: In this article, a new measurement of the high temperature heat capacity of Rh 2 O 3 using differential scanning calorimetry (DSC) is presented, which is significantly different from those given in thermodynamic compilations.
Abstract: The standard Gibbs energy of formation of Rh 2 O 3 at high temperature has been determined recently with high precision. The new data are significantly different from those given in thermodynamic compilations. Accurate values for enthalpy and entropy of formation at 298.15 K could not be evaluated from the new data, because reliable values for heat capacity of Rh 2 O 3 were not available. In this article, a new measurement of the high temperature heat capacity of Rh 2 O 3 using differential scanning calorimetry (DSC) is presented. The new values for heat capacity also differ significantly from those given in compilations. The information on heat capacity is coupled with standard Gibbs energy of formation to evaluate values for standard enthalpy and entropy of formation at 289.15 K using a multivariate analysis. The results suggest a major revision in thermodynamic data for Rh 2 O 3 . For example, it is recommended that the standard entropy of Rh 2 O 3 at 298.15 K be changed from 106.27 J mol -1 K -1 given in the compilations of Barin and Knacke et al. to 75.69 J mol -1 K -1 . The recommended revision in the standard enthalpy of formation is from -355.64 kJ mol -1 to -405.53 kJ mol -1 .

32 citations


Journal ArticleDOI
TL;DR: In this article, the relationship between the corrected selectivity coefficient, Kc (Me) (Me = Zn, Pb), and fraction of the exchanged Me2+ ions in zeolite A, f Me,Z, were determined from corresponding exchange isotherms.
Abstract: Relationships between the corrected selectivity coefficient, Kc (Me) (Me = Zn, Pb), and fraction of the exchanged Me2+ ions in zeolite A, f Me,Z, were determined from the corresponding exchange isotherms. The exchange isotherms were obtained by measuring the equilibrium concentrations of sodium and Me2+ ions in both the solid and the liquid phase at constant total-ion concentrations and different temperatures in the range from 20°C to 60°C. Thermodynamic equilibrium constants, Ka (Me), calculated from the corresponding Kielland's plots (lnKC (Me) vs.f Me,Z plots) were used for the calculation of the appropriate values of standard free energy, ΔG°(Me), standard enthalpy, ΔH°(Me), and standard entropy, ΔS°(Me).

31 citations


Journal ArticleDOI
TL;DR: In this paper, the authors measured the potentials of solute molecules in aqueous acetone and tetramethyl urea (TMU) solutions, and concluded that three distinctively different mixing schemes are operative depending on the composition range.

23 citations


Journal ArticleDOI
TL;DR: The ion exchange and sorption properties of crystalline Tin bis(monohydrogen orthophosphate) monohydrate of composition Sn(HPO(4))(2).H(2)O were studied in an aqueous solution of KCl over the temperature range 300-320 K, varying the pH and metal ion concentration in the solution.

Journal ArticleDOI
TL;DR: In this paper, the standard molar enthalpies of combustion, in oxygen, at T ǫ = 298.15 K, Δ c H m o, measured by static bomb combustion calorimetry.

Journal ArticleDOI
TL;DR: In this article, the authors studied the hydrogen absorption in PuNi 3 type rhombohedral Tb 1− x Zr x Fe 3 (x =01, 02, 03) system in the temperature range 75≤ T (°C)≤150 at an initial pressure of 20 bar by fitting the experimental kinetic data to a second order rate equation.

Journal ArticleDOI
TL;DR: In this paper, the temperature dependence of the molar heat capacity of hydrofullerene C60H36 between 5 and 340 K was determined by adiabatic vacuum calorimetry with an error of about 0.2%.
Abstract: The temperature dependence of the molar heat capacity (C p o ) of hydrofullerene C60H36 between 5 and 340 K was determined by adiabatic vacuum calorimetry with an error of about 0.2%. The experimental data were used for the calculation of the thermodynamic functions of the compound in the range 0 to 340 K. It was found that at T=298.15 K and p=101.325 kPa C p o (298.15)=690.0 J K –1 mol –1 , H o (298.15)–H o (0)= 84.94 kJ mol –1 , S o (298.15)=506.8 J K –1 mol –1 , G o (298.15)–H o (0)= –66.17 kJ mol –1 . The standard entropy of formation of hydrofullerene C60H36 and the entropy of reaction of its formation by hydrogenation of fullerene C60 with hydrogen were estimated and at T=298.15 K they were ΔfS o = –2188.4 J K –1 mol –1 and ΔrS o = –2270.5 J K –1 mol –1 , respectively.

Journal ArticleDOI
TL;DR: In this article, the authors explored the application of the tetraphenylarsonium tetrahenylborate (TATB) assumptions in obtaining the hydration entropy of ions and compared the results with those based on the widely accepted estimate of the standard entropy of the aqueous hydrogen ion based on thermocell data.

Journal ArticleDOI
TL;DR: In this paper, it was shown that for solid state organic substances ToSo≈2Qo, the area under a curve comprising the same incremental Cp values plotted against T can be estimated.

Journal ArticleDOI
TL;DR: In this paper, the authors used ANNs with Extended Delta-Bar-Delta (EDBD) back propagation learning algorithm to predict the standard enthalpy and entropy of 87 acyclic alkanes.
Abstract: Artificial Neural Networks (ANNs) with Extended Delta-Bar-Delta (EDBD) back propagation learning algorithm have been developed to predict the standard enthalpy and entropy of 87 acyclic alkanes. Molecular weight, boiling point and density of the compounds were used as input parameters. The network's architecture and parameters were optimized to give maximum performances. The best network was a 3-6-2 ANN, and the optimum learning epoch was about 1320. The results show that the maximum relative errors of enthalpy and entropy are less than 3%. They reveal that the performances of ANNs for predicting the enthalpy and entropy of alkanes are satisfying.

Journal ArticleDOI
TL;DR: In this paper, the change of oxygen potential, Δ G O 2, for the solid solutions of general formula A y 2+ B z 3+ U 1− y − z O 2+ x was studied by the method of configurational entropy calculation for cations and cation complexes.

Journal ArticleDOI
TL;DR: In this paper, the standard free energies of formation of V 3 Ge and V 5 Ge 3 at high temperature were determined from the activity data, and used in a third-law evaluation of the standard enthalpies of formation at 298 K of all the four intermediate compounds in the vanadium-germanium system.

Journal ArticleDOI
TL;DR: The heat capacity of crystalline NaZr2(AsO4)3 has been measured in the range 7-650 K using precision adiabatic calorimetry and differential scanning (DSC) as mentioned in this paper.
Abstract: The heat capacity C p 0 of crystalline NaZr2(AsO4)3 has been measured in the range 7–650 K using precision adiabatic calorimetry and differential scanning calorimetry. The experimental data have been used to calculate the standard thermodynamic functions of the arsenate: C p 0 , enthalpy H 0(T) − H 0(0), entropy S 0(T), and Gibbs function G 0(T) − H 0(0) from T → 0 to 650 K. The standard entropy of its formation from elements is Δf S 0(NaZr2(AsO4)3, cr, 298.15 K) = −1087 ± 1 J/(mol K).

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the influence of temperature, the addition of KBr, and the concentrations of DTA and TX100 on the complex formation between free DTA cations and nonionic micelles in solution.
Abstract: The nature and thermodynamics of interactions of the cationic surfactant dodecyltri methylammonium bromide (DTA) with the nonionic surfactant Triton X-100 (TX100) in mixtures are studied using the potentiometric method. We investigate the influence of temperature, the addition of KBr, and the concentrations of DTA and TX100 on the complex formation between free DTA cations and TX100 nonionic micelles in solution. Binding isotherms, distribution coefficients Kx, and stoichiometric equilibrium constants K1 are determined from the experimental data. The standard free energy change (ΔG1°), the standard enthalpy change (ΔH1°) and the standard entropy change (ΔS 1°) are calculated for transferring the free DTA cation from the aqueous bulk phase to the TX100 nonionic micelle phase. Our results support the assumption that hydrophobic interactions are the most important in this binding process.

Journal ArticleDOI
01 Apr 2000
TL;DR: The driving force for vesicle formation can be understood in terms of overlap of the thermally labile hydrophobic hydration shells of the alkyl chains.
Abstract: Titration microcalorimetry is used to study the influences of iodide, bromide, and chloride counterions on the aggregation of vesicle-forming 1-methyl-4-(2-pentylheptyl)pyridinium halide surfactants. Formation of vesicles by these surfactants was characterised using transmission electron microscopy. When the counterion is changed at 303 K through the series iodide, bromide, to chloride, the critical vesicular concentration (cvc) increases and the enthalpy of vesicle formation changes from exo- to endothermic. With increase in temperature to 333 K, vesicle formation becomes strongly exothermic. Increasing the temperature leads to a decrease in enthalpy and entropy of vesicle formation for all three surfactants. However the standard Gibbs energy for vesicle formation is, perhaps surprisingly, largely unaffected by an increase in temperature, as a consequence of a compensating change in both standard entropy and standard enthalpy of vesicle formation. Interestingly, standard isobaric heat capacities of vesicle formation are negative, large in magnitude but not strikingly dependent on the counterion. We conclude that the driving force for vesicle formation can be understood in terms of overlap of the thermally labile hydrophobic hydration shells of the alkyl chains.

01 Jan 2000
TL;DR: In this article, the authors explored the application of the tetraphenylarsonium tetrahenyl borate (TATB) assumptions in obtaining the hydration entropy of ions and compared the results with those based on the widely accepted estimate of the standard entropy of the aqueous hydrogen i on based on thermocell data.
Abstract: The hydration entropy of ions is calculated from their entropy in the ideal gaseous state and the standard entropy of their aqueous solutions. The application of the tetraphenylarsonium tetraphenyl borate (TATB) and the cognate tetraphenyl phosphonium tetraphenyl borate (TPTB) assumptions in obtaining the latter is explored, using newly determined heat capacity data for crystalline tetraphenyl phosphonium and arsonium perchlorates, their redetermined solubility data, both over a temperature interval, and data from the literature. The results are compared with those based on the widely accepted estimate of the standard entropy of the aqueous hydrogen i on based on thermocell data.

Journal ArticleDOI
TL;DR: In this article, the molar heat capacities of NiSi have been determined by low-temperature adiabatic calorimetry at temperatures between 8 and 400 K. From the heat capacity data the derived thermodynamic functions Δ0TH0 and S0 were calculated.
Abstract: The molar heat capacities of NiSi have been determined by low-temperature adiabatic calorimetry at temperatures between 8 and 400 K. From the heat capacity data the derived thermodynamic functions Δ0TH0 and S0 were calculated. At T = 298.15 K a molar standard heat capacity of 45.55 ± 0.05 J K−1 mol−1 and a molar standard entropy of 47.58 ± 0.04 J K−1 mol−1 have been found. The entropy of formation for NiSi was calculated to be −1.11 ± 0.08 J K−1 mol−1.

Journal Article
TL;DR: In this article, the effects of temperature, surfactant structure, alcohols (methanol, ethanol, propanol, isopropanol) and mixed solvents (alcohol-water with various volume ratio) on the micellar properties of two quaternary ammonium salts (QAS) with similar structure (hexadecyltrimethyl- and hexadecyldimethylethyl ammonium bromides) were studied using conductometric techniques.
Abstract: The effects of temperature, surfactant structure, alcohols (methanol, ethanol, propanol, isopropanol) and mixed solvents (alcohol-water with various volume ratio) on the micellar properties of two quaternary ammonium salts (QAS) with similar structure (hexadecyltrimethyl- and hexadecyldimethylethyl ammonium bromides) were studied using conductometric techniques. The effects of butanols (n-butanol, i-butanol, t-butanol) on the critical micelle concentrations (c.m.c.) of five surfactants-dodecyl-, tetradecyl-, hexadecyl-, octadecyltrimethyl-ammonium and hexadecyldimethylethylammonium bromides were also studied. The c.m.c., degree of counterion binding (β) and thermodynamic parameters (standard molar Gibbs energy, molar enthalpy and molar entropy) of micellization were calculated and compared with the measured conductivity dependences.

Journal ArticleDOI
TL;DR: In this article, the initial temperature coefficients were measured for a thermogalvanic cell composed of two silver chloride electrodes in water-methanol solutions (WMS) of hydrogen chlorite at 298 K.
Abstract: The initial temperature coefficients are measured for the voltage of a thermogalvanic cell composed of two silver chloride electrodes in water-methanol solutions (WMS) of hydrogen chlorite at 298 K. The experimental results and earlier studies of thermoelectric properties of WMS of alkali metal halides are used to determine the entropy and partial molar entropy of the hydrogen ion moving in solution, the entropy change during its solvation, and the entropy carried by the hydrogen ion and a stoichiometric mixture of H+ and Cl- ions in various WMS. The influence of composition of a mixed solvent on the entropy characteristics of the hydrogen ion is analyzed.