Heat capacity and thermodynamic functions of LuPO4 in the range 0-320 K

The heat capacity of LuPO₄ was measured in the temperature range 6.51-318.03 K. Smoothed experimental values of the heat capacity were used to calculate the entropy, enthalpy and Gibbs free energy from 0 to 320 K. Under standard conditions these thermodynamic values are: (298.15 K) = 100.0 ± 0.1 J K⁻¹ mol⁻¹, S⁰(298.15 K) = 99.74 ± 0.32 J K⁻¹ mol⁻¹, H⁰(298.15 K) − H⁰(0) = 16.43 ± 0.02 kJ mol⁻¹, −[G⁰(298.15 K) − H⁰(0)]/T = 44.62 ± 0.33 J K⁻¹ mol⁻¹. The standard Gibbs free energy of formation of LuPO₄ from elements Δ_fG⁰(298.15 K) = −1835.4 ± 4.2 kJ mol⁻¹ was calculated based on obtained and literature data.     

Heat capacity and thermodynamic functions of nano-TiO2 rutile in relation to bulk-TiO2 rutile

Several conflicting reports have suggested that the thermodynamic properties of materials change with respect to particle size. To investigate this, we have measured the constant pressure heat capacities of three 7 nm TiO₂ rutile samples containing varying amounts of surface-adsorbed water using a combination of adiabatic and semi-adiabatic calorimetric methods. These samples have a high degree of chemical, phase, and size purity determined by rigorous characterization. Molar heat capacities were measured from T = (0.5 to 320) K, and data were fitted to a sum of theoretical functions in the low temperature (T < 15 K) range, orthogonal polynomials in the mid temperature range (10 > T/K > 75), and a combination of Debye and Einstein functions in the high temperature range (T > 35 K). These fits were used to generate $\mathit{Cp}\text{,}{\text{m}}^{\circ }$, ${\mathrm{\Delta }}_0^{\text{T}}{S}_{\text{m}}^{\circ }$, ${\mathrm{\Delta }}_0^{\text{T}}{H}_{\text{m}}^{\circ }$, and ${\phi }_{\text{m}}^{\circ }$ values at selected temperatures between (0.5 and 300) K for all samples. Standard molar entropies at T = 298.15 K were calculated to be (62.066, 59.422, and 58.035) J · K⁻¹ · mol⁻¹ all with a standard uncertainty of 0.002·${\mathrm{\Delta }}_0^{\text{T}}{S}_{\text{m}}^{\circ }$ for samples TiO₂·0.361H₂O, TiO₂·0.296H₂O, and TiO₂·0.244H₂O, respectively. These and other thermodynamic values were then corrected for water content to yield bare nano-TiO₂ thermodynamic properties at T = 298.15 K, and we show that the resultant thermodynamic properties of anhydrous TiO₂ rutile nanoparticles equal those of bulk TiO₂ rutile within experimental uncertainty. Thus we show quantitatively that the difference in thermodynamic properties between bulk and nano-TiO₂ must be attributed to surface adsorbed water.     

Low-temperature heat capacity and thermodynamic properties of crystalline carboxin (C12H13NO2S)

Carboxin was synthesized and its heat capacities were measured with an automated adiabatic calorimeter over the temperature range from 79 to 380 K. The melting point, molar enthalpy (Δ_fusH_m) and entropy (Δ_fusS_m) of fusion of this compound were determined to be 365.29±0.06 K, 28.193±0.09 kJ mol⁻¹ and 77.180±0.02 J mol⁻¹ K⁻¹, respectively. The purity of the compound was determined to be 99.55 mol% by using the fractional melting technique. The thermodynamic functions relative to the reference temperature (298.15 K) were calculated based on the heat capacity measurements in the temperature range between 80 and 360 K. The thermal stability of the compound was further investigated by differential scanning calorimetry (DSC) and thermogravimetric (TG) analysis. The DSC curve indicates that the sample starts to decompose at ca. 290 °C with the peak temperature at 292.7 °C. The TG-DTG results demonstrate the maximum mass loss rate occurs at 293 °C corresponding to the maximum decomposition rate.     

Heat capacity and thermodynamic properties of crystalline ornidazole (C7H10ClN3O3)

The molar heat capacities of 1-(2-hydroxy-3-chloropropyl)-2-methyl-5-nitroimidazole (Ornidazole) (C₇H₁₀ClN₃O₃) with purity of 99.72 mol% were measured with an adiabatic calorimeter in the temperature range between 79 and 380 K. The melting-point temperature, molar enthalpy, Δ_fusH_m, and entropy, Δ_fusS_m, of fusion of this compound were determined to be 358.59±0.04 K, 21.38±0.02 kJ mol⁻¹ and 59.61±0.05 J K⁻¹ mol⁻¹, respectively, from fractional melting experiments. The thermodynamic function data relative to the reference temperature (298.15 K) were calculated based on the heat capacities measurements in the temperature range from 80 to 380 K. The thermal stability of the compound was further investigated by DSC and TG. From the DSC curve an intensive exothermic peak assigned to the thermal decomposition of the compound was observed in the range of 445-590 K with the peak temperature of 505 K. Subsequently, a slow exothermic effect appears when the temperature is higher than 590 K, which is probably due to the further decomposition of the compound. The TG curve indicates the mass loss of the sample starts at about 440 K, which corresponds to the decomposition of the sample.     

A calorimetric and thermodynamic investigation of A2[(UO2)2(MoO4)O2] compounds with A = K and Rb and calculated phase relations in the system (K2MoO4 + UO3 + H2O)

A calorimetric and thermodynamic investigation of two alkali-metal uranyl molybdates with general composition A₂[(UO₂)₂(MoO₄)O₂], where A = K and Rb, was performed. Both phases were synthesized by solid-state sintering of a mixture of potassium or rubidium nitrate, molybdenum (VI) oxide and gamma-uranium (VI) oxide at high temperatures. The synthetic products were characterised by X-ray powder diffraction and X-ray fluorescence methods. The enthalpy of formation of K₂[(UO₂)₂(MoO₄)O₂] was determined using HF-solution calorimetry giving Δ_fH° (T = 298 K, K₂[(UO₂)₂(MoO₄)O₂], cr) = −(4018 ± 8) kJ · mol⁻¹. The low-temperature heat capacity, С_р°, was measured using adiabatic calorimetry from T = (7 to 335) K for K₂[(UO₂)₂(MoO₄)O₂] and from T = (7 to 326) K for Rb₂[(UO₂)₂(MoO₄)O₂]. Using these С_р° values, the third law entropy at T = 298.15 K, S°, is calculated as (374 ± 1) J · K⁻¹ · mol⁻¹ for K₂[(UO₂)₂(MoO₄)O₂] and (390 ± 1) J · K⁻¹ · mol⁻¹ for Rb₂[(UO₂)₂(MoO₄)O₂]. These new experimental results, together with literature data, are used to calculate the Gibbs energy of formation, Δ_fG°, for both phases giving: Δ_fG° (T = 298 K, K₂[(UO₂)₂(MoO₄)O₂], cr) = (−3747 ± 8) kJ · mol⁻¹ and Δ_fG° (T = 298 K, Rb₂[(UO₂)₂(MoO₄)], cr) = −3736 ± 5 kJ · mol⁻¹. Smoothed С_р°(Т) values between 0 K and 320 K are presented, along with values for S° and the functions [H°(T) − H°(0)] and [G°(T) − H°(0)], for both phases. The stability behaviour of various solid phases and solution complexes in the (K₂MoO₄ + UO₃ + H₂O) system with and without CO₂ at T = 298 K was investigated by thermodynamic model calculations using the Gibbs energy minimisation approach.     

Benchmark thermodynamic properties of alkanediamines: Experimental and theoretical study

Vapor pressures of (dl)-1,2-propanediamine and 2-methyl-1,2-propanediamine were measured using the transpiration method. Molar enthalpies of vaporization were derived from the vapor pressure temperature dependence. Thermodynamic data on alkanediamines available in the literature were collected and treated uniformly. Consistency of the experimental data set for alkanediamines was evaluated with group-contribution and quantum-chemical methods.The standard molar entropy of formation and the standard molar Gibbs function of formation have been calculated. Vaporization and formation enthalpies of alkanediamines of benchmark quality are recommended for practical thermochemical calculations and validation of empirical and theoretical methods.     

Crystal structure, spectroscopy and thermodynamic properties of MVWO6(M – Li, Na)

In the present work lithium (sodium) vanadium tungsten oxides with brannerite structure is refined by the Rietveld method (space group C2/m, Z=2). IR and Raman spectroscopy was used to assign vibrational bands and determine structural particularities. The diffuse reflectance spectra allow to calculate bandgap for M^IVWO₆(M^I – Li, Na). The temperature dependences of heat capacity have been measured first in the range from 7 to 350 K for these compounds and then between 330 and 640 K, respectively, by precision adiabatic vacuum and dynamic calorimetry. The experimental data were used to calculate standard thermodynamic functions, namely the heat capacity C_p^o(T), enthalpy H^o(T)−H^o(0), entropy S^o(T)−S^o(0) and Gibbs function G^o(T)−H^o(0), for the range from T→0 to 640 K. The differential scanning calorimetry was applied to measure decomposition temperature of compounds under study.     

Thermodynamic properties of carbosilane dendrimers of the third to the sixth generations with terminal butyl groups in the range from T → 0 to 600 K

In the present work temperature dependences of heat capacity of carbosilane dendrimers with butyl terminal groups of the third and the fourth generations as well as of the fifth and the sixth generations have been determined first in the range from 6 to 340 K and between 6 and 600 K, respectively, by precision adiabatic vacuum and dynamic calorimetry. In the above temperature ranges the physical transformations have been detected and their thermodynamic characteristics have been estimated and analyzed. The experimental data were used to calculate standard thermodynamic functions, namely the heat capacity , enthalpy H^o(T) − H^o(0), entropy S^o(T) − S^o(0) and Gibbs function G^o(T) − H^o(T), for the range from T → 0 to (340–600) K. Linear dependences of changing the corresponding thermodynamic functions of the dendrimers on their molecular weight and the number of butyl groups on an outer sphere have been determined.     

Additive prediction of thermodynamic functions of hydrofluorides

Summary The experimental data available on the thermodynamic functions ⁰ forMF·nHF hydrofluorides [M=Li, Na, K, Rb, Cs, NH₄, Ag(I) and Tl(I);n=1–3] have been evaluated additively. The unknown values of ⁰ forn=0÷7 are predicted.

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Additive Voraussagen der thermodynamischen Funktionen von Hydrogenfluoriden (Kurze Mitt.)

Zusammenfassung Die vorhandenen experimentellen Daten über die thermodynamischen Funktionen ⁰ von HydrogenfluoridenMF·nHF [M=Li, Na, K, Rb, Cs, NH₄, Ag(I) und Tl(I);n=1–3] werden linear ausgeglichen und die fehlendenden Werte für ⁰ mitn=0÷7 vorausgesagt.

     

Heat capacity and thermodynamic properties of N-(2-cyanoethyl) aniline (C9H10N2)

The low temperature heat capacities of N-(2-cyanoethyl)aniline were measured with an automated adiabatic calorimeter over the temperature range from 83 to 353 K. The temperature corresponding to the maximum value of the apparent heat capacity in the fusion interval, molar enthalpy and entropy of fusion of this compound were determined to be 323.33 ± 0.13 K, 19.4 ± 0.1 kJ mol⁻¹ and 60.1 ± 0.1 J K⁻¹ mol⁻¹, respectively. Using the fractional melting technique, the purity of the sample was determined to be 99.0 mol% and the melting temperature for the tested sample and the absolutely pure compound were determined to be 323.50 and 323.99 K, respectively. A solid-to-solid phase transition occurred at 310.63 ± 0.15 K. The molar enthalpy and molar entropy of the transition were determined to be 980 ± 5 J mol⁻¹ and 3.16 ± 0.02 J K⁻¹ mol⁻¹, respectively. The thermodynamic functions of the compound [H_T − H_298.15] and [S_T − S_298.15] were calculated based on the heat capacity measurements in the temperature range of 83–353 K with an interval of 5 K.     

Heat capacity and standard molar enthalpy of formation of crystalline 2,6-dicarboxypyridine (C7H5NO4)

Low-temperature heat capacity C_p,m of 2,6-dicarboxypyridine (C₇H₅NO₄; CAS 499-83-2) was precisely measured in the temperature range from (80 to 378) K with a high precision automated adiabatic calorimeter. No phase transition or thermal anomaly was observed in this range. The thermodynamic functions [H_T − H_298.15] and [S_T − S_298.15] were calculated in the range from (80 to 378) K. The standard molar enthalpy of combustion and the standard molar enthalpy of formation of the compound have been determined, and , by means of a precision oxygen-bomb combustion calorimeter at T = 298.15 K. The thermodynamic properties of the compound were further investigated through differential scanning calorimeter (DSC) and the thermogravimetric (TG) analysis.     

Experimental and theoretical study of thermodynamic properties of levoglucosan

The heat capacity of levoglucosan was measured over the temperature range (5 to 370) K by adiabatic calorimetry. The temperatures and enthalpies of a solid-phase transition and fusion for the compound were found by DSC. The obtained results allowed us to calculate thermodynamic properties of crystalline levoglucosan in the temperature range (0 to 384) K. The enthalpy of sublimation for the low-temperature crystal phase was found from the temperature-dependent saturated vapor pressures determined by the Knudsen effusion method. The thermodynamic properties of gaseous levoglucosan were calculated by methods of statistical thermodynamics using the molecular parameters from quantum chemical calculations. The enthalpy of formation of the crystalline compound was found from the experiments in a combustion calorimeter. The gas-phase enthalpy of formation was also obtained at the G4 level of theory. The thermodynamic analysis of equilibria of levoglucosan formation from cellulose, starch, and glucose was conducted.     

High temperature enthalpy and heat capacity of GaN

The heat capacity and the heat content of gallium nitride were measured by calvet calorimetry (320-570 K) and by drop calorimetry (670-1270 K), respectively. The temperature dependence of the heat capacity in the form C_pm=49.552+5.440×10⁻³T−2.190×10⁶T⁻²+2.460×10⁸T⁻³ was derived by the least squares method. Furthermore, thermodynamic functions calculated on the basis of our experimental results and literature data on the molar entropy and the heat of formation of GaN are given.     

Heat capacity measurements on uranium–cerium mixed oxides by differential scanning calorimetry

Uranium–cerium mixed oxides of three different compositions (U_0.2Ce_0.8)O₂, (U_0.5Ce_0.5)O₂ and (U_0.8Ce_0.2)O₂, were prepared by combustion synthesis and characterized by XRD. The compositional characterization was done by ICP-AES. Heat capacity measurements employed a heat flux type differential scanning calorimeter from 280 to 820 K. The heat capacity values of (U_0.2Ce_0.8)O₂, (U_0.5Ce_0.5)O₂ and (U_0.8Ce_0.2)O₂ at 298 K are 62.8, 64.2 and 70.1 J K⁻¹ mol⁻¹, respectively. Enthalpy increment, entropy and Gibbs energy function were computed from the heat capacity data.     

Thermodynamic functions of α,α-trehalose dihydrate and of α,β-trehalose monohydrate at temperatures from 13 K to 300 K

Thermodynamic properties at low temperatures were investigated for α,α-trehalose dihydrate and α,β-trehalose monohydrate. The heat capacities were measured using an adiabatic calorimeter at temperatures between 13 K and 300 K. The heat capacity data were expressed as a function of temperature, T, by a polynominal of forth to sixth order, with which thermodynamic functions, enthalpy, entropy, and Gibbs free energy, were determined.     

S6 Isomer of C60(CF3)12: Synthesis,properties and thermodynamic functions

A crystalline form of S₆-С₆₀(CF₃)₁₂ was synthesized in an amount sufficient for reliable experimental investigation. We determined the enthalpy of combustion of S₆-С₆₀(CF₃)₁₂ in oxygen and its heat capacity, which made possible to derive the thermodynamic functions of S₆-С₆₀(CF₃)₁₂, namely the enthalpy of formation, the entropy and the Gibbs energy at T = 298.15 K. These experimental thermochemical data enabled estimation of the formation energy for a broad range of other trifluoromethylated compounds C₆₀(CF₃)_n, with n = (2–18; 24), on the basis of their DFT calculated relative energies.