Entropy Of Formation Research Articles

Thermodynamic and thermal properties of the C60-l-lysine derivative

In the present research, the low-temperature molar heat capacity, Cp,m°, of C60 – l-lysine derivative was measured using adiabatic calorimetry from T=13K to T=326K. The respective molar third law entropy at T=298.15K, Sm°, was calculated giving (1110±3)J·K−1·mol−1 for C60 – l-lysine derivative. Smoothed Cp,m°(T) values between T→0K and 320K are presented along with the values for Sm° and the functions [Hm°(T) – Hm°(0)] and [Gm°(T) – Hm°(0)]. The standard molar entropy of formation, ΔfSm°, at T=298.15K was calculated for the compound under study in the crystalline state giving −1916±5J·K−1·mol−1. The complex thermal analysis of the C60-Lys crystallohydrate was performed from T=300 to T=1323K.

Thermochemical study Mg–Fe amphiboles

The paper presents data on the thermochemical study (high-temperature melt calorimetry in a Tian–Calvet microcalorometer) of two natural Mg–Fe amphiboles: anthophyllite Mg2.0(Mg4.8Fe0.2 2+)[Si8.0O22](OH)2 from Kukh-i-Lal, southwestern Pamirs, Tajikistan, and gedrite Na0.4Mg2.0(Mg1.7Fe0.2 2+Al1.3)[Si6.3Al1.7O22](OH)2 from the Kola Peninsula, Russia. The enthalpy of formation from elements is obtained as–12021 ± 20 kJ/mol for anthophyllite and as–11545 ± 12 kJ/mol for gedrite. The standard entropy, enthalpy, and Gibbs energy of formation are evaluated for Mg–Fe amphiboles of theoretical composition.

Facing the challenge of predicting the standard formation enthalpies of n-butyl-phosphate species with ab initio methods.

Tributyl-phosphate (TBP), a ligand used in the PUREX liquid-liquid separation process of spent nuclear fuel, can form an explosive mixture in contact with nitric acid that might lead to a violent explosive thermal runaway. In the context of safety of a nuclear reprocessing plant facility, it is crucial to predict the stability of TBP at elevated temperatures. So far, only the enthalpies of formation of TBP are available in the literature with rather large uncertainties, while those of its degradation products, di-(HDBP) and mono-(H2MBP), are unknown. In this goal, we have used state-of-the art quantum chemical methods to compute the formation enthalpies and entropies of TBP and its degradation products di-(HDBP) and mono-(H2MBP) in gas and liquid phases. Comparisons of levels of quantum chemical theory revealed that there are significant effects of correlation on their electronic structures, pushing for the need of not only high level of electronic correlation treatment, namely, local coupled cluster with single and double excitation operators and perturbative treatment of triple excitations, but also extrapolations to the complete basis to produce reliable and accurate thermodynamics data. Solvation enthalpies were computed with the conductor-like screening model for real solvents [COSMO-RS], for which we observe errors not exceeding 22 kJ mol-1. We thus propose with final uncertainty of about 20 kJ mol-1 standard enthalpies of formation of TBP, HDBP, and H2MBP which amounts to -1281.7 ± 24.4, -1229.4 ± 19.6, and -1176.7 ± 14.8 kJ mol-1, respectively, in the gas phase. In the liquid phase, the predicted values are -1367.3 ± 24.4, -1348.7 ± 19.6, and -1323.8± 14.8 kJ mol-1, to which we may add about -22 kJ mol-1 error from the COSMO-RS solvent model. From these data, the complete hydrolysis of TBP is predicted as an exothermic phenomena but showing a slightly endergonic process.

Gaining Thermodynamic Insight From Distinct Glass Formation Kinetics of Structurally Similar Organic Compounds

Thermodynamic and kinetic aspects of crystallization of 12 structurally similar organic compounds were investigated from the supercooled liquid state by calorimetric and rheologic measurements. Based on their crystallization behaviors, these compounds were divided into 3 categories: stable glass formers, poor glass formers, and good glass formers with poor stability on reheating. Correlation was sought between thermodynamic quantities and glass formation based on nucleation and crystal growth theories. Larger values of enthalpy of fusion and melting point were found to correlate with poor glass-forming ability. Conversely, lower entropy of fusion was found to correlate with glass formation. Examination of kinetic aspects of glass formation revealed 2 important facets of good glass formers, that is, rapid increase in viscosity on supercooling and high melting point viscosity compared with non-glass formers. A broader relationship was sought between entropy of fusion and glass formation by including several glass formers from literature. Our analysis indicated that good glass formers tend to have an entropy of fusion closer to 0.3 J cm−3 K−1. The structural similarity of the compounds in this study provides insights regarding the nature of intermolecular interactions responsible for the observed effect on entropy of fusion, viscosity, and crystallization kinetics.

Synthesis of diethyl carbonate from ethanol through different routes: A thermodynamic and comparative analysis

In this study, thermodynamic analysis of various possible synthesis routes of diethyl carbonates (DEC), a benign organic carbonate, was carried out and a comparative analysis was performed. Chemical equilibrium constants at standard conditions were calculated using Gibbs free energy of the system. The Benson group contribution method was used to estimate standard heat of formation and standard entropy change of some raw materials/components like dimethyl carbonate. Variation of heat capacity (Cp) with temperature was estimated for different components from the Rozicka‐Domalski model. Variation of chemical equilibrium constants with temperature and pressure was studied for various routes. Synthesis of DEC from ethylene carbonate (EC) was also found to be better considering equilibrium constants at room temperature. The CO2 route was found to be the most unfavourable route for DEC synthesis due to stability of CO2 molecules. Moreover, DEC synthesis through the urea route was found to be best at high temperatures since the equilibrium constants were found to increase exponentially. Experiments were conducted for DEC synthesis using the EC route at two temperatures. Activity coefficients were calculated using the UNIFAC model. Experimentally and theoretically determined chemical equilibrium constant values were found to be similar. PRO/II was also used to minimize Gibbs free energy of the system and estimate the equilibrium constants and the results were comparable with those obtained by the equilibrium constant method and the trend was found to be the same for both the methods.

Enthalpies of formation of polyhalite: A mineral relevant to salt repository

Polyhalite is an important coexisting mineral with halite in salt repositories for nuclear waste disposal, such as Waste Isolation Pilot Plant (WIPP) in Carlsbad, New Mexico. The thermal stability of this mineral is a key knowledge in evaluating the integrity of a salt repository in the long term, as water may release due to thermal decomposition of polyhalite. Previous studies on structural evolution of polyhalite at elevated temperatures laid the basis for detailed calorimetric measurements. Using high-temperature oxide-melt drop-solution calorimetry at 975K with sodium molybdate as the solvent, we have determined the standard enthalpies of formation from constituent sulfates (ΔH°f,sul), oxides (ΔH°f,ox) and elements (ΔH°f,ele) of a polyhalite sample with the composition of K2Ca2Mg(SO4)4·1.95H2O from the Salado formation at the WIPP site. The obtained results are: ΔH°f,sul=−152.5±5.3kJ/mol, ΔH°f,ox=−1926.1±10.5kJ/mol, and ΔH°f,ele=−6301.2±9.9kJ/mol. Furthermore, based on the estimated formation entropies of polyhalite, its standard Gibbs free energy of formation has been derived to be in the range of −5715.3±9.9kJ/mol to −5739.3±9.9kJ/mol. These determined thermodynamic properties provide fundamental parameters for modeling the stability behavior of polyhalite in salt repositories.

Thermodynamic properties of liquid copper–lanthanum alloys

Mixing enthalpies of alloys in the Cu–La system are measured using isoperibolic calorimetry method over the ranges 0 < x La < 0.185 at 1400–1430 K and 0.659 < x La < 1 at 1370 K. They have moderate exothermic values over the whole concentration range and agree with literature data. Activities of the components, enthalpies and entropies of formation of intermetallics in this system, and its phase diagram are optimized using an ideal associated solution (IAS) model, and agree with most literature data. The updated thermodynamic properties can be used in further investigation of multicomponent systems based on the binary Cu–La.

Structural and thermodynamic study of dicesium molybdate Cs2Mo2O7: Implications for fast neutron reactors

The structure of α-Cs2Mo2O7 (monoclinic in space group P21/c), which can form during irradiation in fast breeder reactors in the space between nuclear fuel and cladding, has been refined in this work at room temperature from neutron diffraction data. Furthermore, the compounds' thermal expansion and polymorphism have been investigated using high temperature X-ray diffraction combined with high temperature Raman spectroscopy. A phase transition has been observed at Ttr(α→β)=(621.9±0.8)K using Differential Scanning Calorimetry, and the structure of the β-Cs2Mo2O7 phase, orthorhombic in space group Pbcm, has been solved ab initio from the high temperature X-ray diffraction data. Furthermore, the low temperature heat capacity of α-Cs2Mo2O7 has been measured in the temperature range T=(1.9–313.2)K using a Quantum Design PPMS (Physical Property Measurement System) calorimeter. The heat capacity and entropy values at T=298.15K have been derived as Cp,mo(Cs2Mo2O7,cr,298.15K)=(211.9±2.1)JK−1mol−1 and Smo(Cs2Mo2O7,cr,298.15K)=(317.4±4.3)JK−1mol−1. When combined with the enthalpy of formation reported in the literature, these data yield standard entropy and Gibbs energy of formation as ΔfSmo(Cs2Mo2O7,cr,298.15K)=−(628.2±4.4)JK−1mol−1 and ΔfGmo(Cs2Mo2O7,cr,298.15K)=−(2115.1±2.5)kJmol−1. Finally, the cesium partial pressure expected in the gap between fuel and cladding following the disproportionation reaction 2Cs2MoO4=Cs2Mo2O7+2Cs(g)+ 1/2 O2(g) has been calculated from the newly determined thermodynamic functions.

Spectroscopic and conductometric study of interaction of anionic surfactants with [Co(phen)3]F2·2H2O complex

A new complex [Co(phen)3]F2·2H2O has been synthesized and characterized by elemental analysis, FTIR studies, magnetic measurements, electronic absorption measurements and single crystal X-ray diffraction analysis. The crystals are triclinic in the P-1 space group, with a=11.9520(8), b=12.8152(9), c=15.1013(11)Å, α=98.175(2)°, β=91.601(2)°, γ=114.8700(10)°. The crystal structure displays OH⋯F and OH⋯O hydrogen-bond interactions. Solubilization of [Co(phen)3]F2·2H2O by anionic surfactants sodium dodecyl sulphate (SDS) and sodium stearate (SS), in aqueous solutions in the premicellar and micellar concentration ranges has been investigated by using UV–visible spectroscopy and electrical conductivity measurements. The equilibrium model was used to evaluate thermodynamic parameters of complex-surfactant interaction like standard entropy (ΔSm), free energy (ΔGm) and enthalpy (ΔHm) of micelle formation. The disruption of structured water in the near environment of hydrophobic groups of surfactants is responsible for the increase in critical micelle concentration (CMC) with the rise in temperature. The negative value of ∆Gm and ΔHm indicate that solubilization of complex in micelles of both surfactants was spontaneous, in addition to enthalpy and entropy driven. UV–visible spectroscopy uncovers the quantitative measure of interaction of complex with surfactant in terms of partition constant (Kx), binding coefficient (Kb), binding free energy (ΔGb) and free energy of partition (ΔGp). The results obtained suggested that the critical micelle concentration of both surfactants is increased due to the presence of complex in micellar medium. Complex exhibited significant radical scavenging potential against DPPH radical and hemolytic effect against RBCs. Further, the complex exhibited no substantial cytotoxic effect against 3T3 cell line.

Diffusion coefficients of transition metals in fcc cobalt

Using first-principles density functional theory (DFT), we calculate the diffusivities of 32 different solute elements—all transition metals, together with Al and Si—in fcc cobalt within the formalism of the five-frequency model. For self-diffusion in fcc cobalt, we compare the accuracy of various approximations to the exchange-correlation energy functional of DFT in estimating the activation energy, and find that only the Perdew-Burke-Ernzerhof (PBE) approximation agrees well with experimental reports and all other functionals largely overestimate it. Our calculations also show that an accurate estimation of the self-diffusion coefficient requires explicit calculation of the effective jump frequency and vacancy formation entropy via phonons. Using accurate self-diffusion data and scaling all solute-related attempt frequencies with respect to the attempt frequency for self-diffusion using a simple relation involving the atomic mass and melting temperature of the solute yields solute diffusivities in excellent agreement with experiments, where such data is available. We find that large solutes spontaneously relax toward the nearest neighbor vacancy to relieve the misfit strain, and the extent of this relaxation correlates negatively with the migration energy. Thus, in general, larger solutes have lower migration energies and diffuse faster than smaller solutes in fcc cobalt. However, extremely large solutes, e.g., group III elements Sc, Y, Lu, tend to be trapped in an energy valley located halfway toward the vacancy, and monovacancy mediated diffusion may no longer be valid in such cases. Finally, for all the solutes considered, we systematically tabulate the diffusion-related quantities calculated—diffusion prefactors, migration and activation energies—constructing an extensive and accurate first-principles database for solute diffusion in fcc cobalt.

Surface freezing and molecular miscibility of binary fluoroalkanol-alkanol liquid mixture

The surface freezing (SF) of liquid 6-perfluorohexyl hexanol (F6H6OH)–1-dodecanol (C12OH) mixture was studied by surface tension, external reflection absorption FTIR (ERA-FTIR), and X-ray reflectivity (XR) measurements. The surface tension vs. temperature curve of pure C12OH liquid shows a sharp break point at the surface liquid (SL)–SF phase transition temperature Ts. The surface tension of pure F6H6OH, on the other hand, decreases monotonically with increasing temperature. The entropy of surface formation in the SF state of C12OH is large negative due to a well-ordered structure at the surface. The electron density profile determined by XR showed that the C12OH molecules form bilayer stabilized by the hydrogen bonding between hydroxyl groups facing each other through water molecule intercalated in between them. In the F6H6OH–C12OH system, the estimation of surface composition indicated that the SL state is enriched in F6H6OH compared to bulk liquid. The negative excess entropy in the SL layer suggests that F6H6OH molecules form domains at the surface. Furthermore, the surface composition and electron density profile in the SF state indicated that a small amount of F6H6OH mix with C12OH in the SF bilayer in which F6H6OH molecules preferentially exist in the upper layer of the bilayer.

On the pH Dependence of the Potential of Maximum Entropy of Ir(111) Electrodes

Studies over the entropy of components forming the electrode/electrolyte interface can give fundamental insights into the properties of electrified interphases. In particular, the potential where the entropy of formation of the double layer is maximal (potential of maximum entropy, PME) is an important parameter for the characterization of electrochemical systems. Indeed, this parameter determines the majority of electrode processes. In this work, we determine PMEs for Ir(111) electrodes. The latter currently play an important role to understand electrocatalysis for energy provision; and at the same time, iridium is one of the most stable metals against corrosion. For the experiments, we used a combination of the laser induced potential transient to determine the PME, and CO charge-displacement to determine the potentials of zero total charge, (EPZTC). Both PME and EPZTC were assessed for perchlorate solutions in the pH range from 1 to 4. Surprisingly, we found that those are located in the potential region where the adsorption of hydrogen and hydroxyl species takes place, respectively. The PMEs demonstrated a shift by ~30 mV per a pH unit (in the RHE scale). Connections between the PME and electrocatalytic properties of the electrode surface are discussed.

Kinetics process of Tb(III)/Tb couple at liquid Zn electrode and thermodynamic properties of Tb-Zn alloys formation

Electrochemical properties of rare-earth elements in the LiCl-KCl eutectic are important for the pyrometallurgical recycling process of spent nuclear fuels. In this work, the electrochemical properties of Tb (III)/Tb (0) couple were studied by the cyclic voltammetry (CV) at a liquid Zn pool electrode. The results showed that this electrochemical reaction is quasi-reversible with mixed reversible diffusion control and the charge transfer control. The diffusion coefficient of Tb (III) was determined to be in the order of ~10−5 cm2 s−1. Moreover, kinetic parameters, such as the standard rate constants ( k s) and charge transfer coefficient ( α ) for the electroreduction of Tb (III) to Tb (0) at the liquid Zn electrode, were calculated by the Nicholson method at 873 K. Additionally, it was found that Tb-Zn intermetallic compounds were easily to be formed in the measurements. Hence, the reduction process of Tb (III)/Tb (0) couple on the Zn-coated Mo electrode was also studied to obtain more information of the Tb-Zn intermetallic compounds. Electrochemical signals stemming from various intermetallic compounds associated with TbZn12, Tb2Zn17, Tb13Zn58, Tb3Zn11, TbZn3, TbZn2 and TbZn, were observed. The thermodynamic data were thereafter estimated by applying the emf method at 823–923 K. The standard formation Gibbs energies and the standard equilibrium constant of each Tb-Zn intermetallic compounds were also calculated. Finally, enthalpies and entropies of formation and the apparent standard potentials of various Tb-Zn intermetallic compounds were also obtained.

Molecular dynamics and cluster-continuum insights on bulk alcohols effects on SN2 reactions of potassium and cesium fluorides with alkyl halides

Bulk alcohols like tert-butanol have been investigated as reaction medium for SN2 reactions, especially nucleophilic fluorination. Nevertheless, details of alkali metal salts in tert-butanol solution, as well as the transition state solvation, have not been investigated. This work presents a molecular dynamics study of pure tert-butanol and solution of KF in tert-butanol. The interaction and structure of the SN2 transition state in tert-butanol solution has also been investigated using both molecular dynamics and density functional theory calculations. In the last case, the transition state is solvated by a cluster of four tert-butanol molecules and by a dielectric continuum. The present study point out the KF and CsF salts form ion pairs in tert-butanol, and the strong interaction of hydroxyl groups of tert-butanol with both cation and anion, combined with low entropy for formation of cluster in solution, facilitates the solubilization of inorganic salts, although the solubility is predicted be low. The reaction of solubilized KF and CsF has low free energy of activation and the transition states involve participation of the tert-butanol molecules. This fact turns the CsF more reactive than KF. The free energy of activation for CsF reaction with ethyl bromide is predicted to be 28.4kcalmol−1, close to the experimental value of 28.9kcalmol−1 for a similar system.

Thermomechanical stabilization of electron small polarons in SrTiO3 assessed by the quasiharmonic approximation

We predict a predominance diagram for electron defects in the temperature-hydrostatic stress space for $\mathrm{SrTi}{\mathrm{O}}_{3}$ by combining density functional theory and the quasiharmonic approximation. We discovered two regimes where small polarons dominate: under tensile stress at lower temperature due to a larger relaxation volume of the defect $\mathrm{\ensuremath{\Omega}}$, and under compressive stress at higher temperature due to a smaller $\mathrm{\ensuremath{\Omega}}$ and larger formation entropy. This provides a means to modulate the electronic conductivity via controlling the underlying charge carrier. Furthermore, the results challenge the common association between larger $\mathrm{\ensuremath{\Omega}}$ and charge localization by demonstrating that at high temperature the free electron can induce larger $\mathrm{\ensuremath{\Omega}}$ compared to the small polaron. This finding is attributed to the ability of the free electron to generate greater vibrational entropy upon finite isothermal expansion.

Thermodynamic Properties Determination in LiF-CaF2 using Electrochemistry in High Temperature Fused Salts: Application to CeF3

Pyrochemical route is a promising option for spent nuclear fuel recycling. The major step of spent fuel reprocessing is the actinides-lanthanides separation performed by electrochemical processes. In this partitioning strategy, the most radiotoxic elements (actinides) are separated from the lowest ones (lanthanides) to decrease the volume of high activity nuclear waste disposal. The knowledge of thermodynamic properties (such as activities, standard potentials…) of actinides and lanthanides in solution is then crucial to predict their electrochemical behaviour in a complex multi-element system. Thermodynamic calculations have been done on cerium fluoride in the LiF-CaF2 eutectics from 1113 to 1233K with FactSage and HSC 6.1 database. From electrochemical measurements (linear sweep voltammetry, equilibrium potential measurements…), the main thermodynamic properties needed for the electrochemical separation evaluation were determined: standard potentials and activity coefficients in different reference states (liquid or solid reference state, and infinite dilution reference state) and for different composition scales (molarity, molality, or molar fraction), and also standard enthalpy and standard entropy of formation in the 1113-1233K temperature range.Finally, constants which interconnected the infinite dilution reference state and the solid and liquid reference states were evaluated.

Elastic properties, thermal stability, and thermodynamic parameters of MoAlB

MoAlB is the first and, so far, the only transition-metal boride that forms alumina when heated in air and is thus potentially useful for high-temperature applications. Herein, the thermal stability in argon and vacuum atmospheres and the thermodynamic parameters of bulk polycrystalline MoAlB were investigated experimentally. At temperatures above 1708 K, in vacuum and inert atmospheres, this compound incongruently melts into the binary MoB and liquid aluminum metal as confirmed by differential thermal analysis, quenching experiments, x-ray diffraction, and scanning electron microscopy. Making use of that information together with heat-capacity measurements in the 4–1000-K temperature range—successfully modeled as the sum of lattice, electronic, and dilation contributions—the standard enthalpy, entropy, and free energy of formation are computed and reported for the full temperature range. The standard enthalpy of formation of MoAlB at 298 K was found to be −132 ± 3.2 kJ/mol. Lastly, the thermal conductivity values are computed and modeled using a variation of the Slack model in the 300–1600-K temperature range.

Charge-transfer interaction between C60 fullerene and alkylnaphthalenes

ABSTRACTA series of alkylnaphthalenes, namely 1,4-dimethylnaphthalene, 2,6-diethylnaphthalene, 2-ethylnaphthalene and pure naphthalene are not able to form Diels-Alder adducts with C60 fullerene but produce a series of 1:1 charge-transfer complexes (CTC) where the aromatic compounds act as donor and C60 as acceptor. The spectrophotometric analysis of these CTC has permitted to determine the equilibrium constants of the CTC formation at four different temperatures and the relative enthalpies and entropies of formation. The C60-alkylnaphthalenes and C60-naphthalene were identified as weakly bound CTC. Using the Mulliken theory of the CTC also the degree of charge transfer α was determined, confirming the results already suggested by the equilibrium constants, i.e., the weakly interaction between the donor and the acceptor considered.

The thermodynamics of uranium salts and their hydrates – Estimating thermodynamic properties for nuclear and other actinoid materials using the Thermodynamic Difference Rule (TDR)

A comprehensive thermodynamic database of experimental standard enthalpy of formation, ΔfHo values, standard free energies of formation, ΔfGo and standard entropies, So298 for uranium salts and their hydrates at 298K and 1bar pressure is assembled. For many of these materials there exist experimental uncertainties or else multiple values (often considerably different) are listed for the same material. The aim of this paper is to showcase the ability of the Thermodynamic Difference Rule (TDR) to provide quite accurate estimates of such data (usually errors are less than 1%) and to provide guidance as to the most trusted value to adopt. In addition, where possible the TDR has been used to estimate missing literature values. New thermochemical data values are predicted and TDR is not reliant on possession of knowledge of crystal structures.

Enthalpy of formation of natural hydrous iron phosphate: Vivianite

This paper presents the new data on thermodynamic properties of hydrous iron phosphate, vivianite. The thermochemical study of natural vivianite Fe2.322+Fe0.333+ Mg0.35(PO4)2(OH)0.33·7.67H2O (Kerch iron ore basin, Republic of Crimea, Russia) was carried out on a high-temperature heat-flux Tian-Calvet microcalorimeter “Setaram” (France). The mineral was characterized by X-ray microprobe analysis, powder and single-crystal X-ray diffraction, thermal analysis, FTIR, Raman and Mössbauer spectroscopy. The value of ΔfHm0(T=298.15K) for natural vivianite was found to be −(5217±11kJmol−1). The standard values of the entropy, enthalpy and Gibbs energy of formation at T=298.15K for vivianite of theoretical composition Fe32+(PO4)2·8H2O were calculated as (571.0)J(Kmol)−1, −(5119±19)kJmol−1 and −(4439±19)kJmol−1 respectively.