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1.
Heat capacity and enthalpy increments of calcium niobates CaNb2O6 and Ca2Nb2O7 were measured by the relaxation time method (2–300 K), DSC (260–360 K) and drop calorimetry (669–1421 K). Temperature dependencies of the molar heat capacity in the form C pm=200.4+0.03432T−3.450·106/T 2 J K−1 mol−1 for CaNb2O6 and C pm=257.2+0.03621T−4.435·106/T 2 J K−1 mol−1 for Ca2Nb2O7 were derived by the least-squares method from the experimental data. The molar entropies at 298.15 K, S m0(CaNb2O6, 298.15 K)=167.3±0.9 J K−1 mol−1 and S m0(Ca2Nb2O7, 298.15 K)=212.4±1.2 J K−1 mol−1, were evaluated from the low temperature heat capacity measurements. Standard enthalpies of formation at 298.15 K were derived using published values of Gibbs energy of formation and presented heat capacity and entropy data: Δf H 0(CaNb2O6, 298.15 K)= −2664.52 kJ molt-1 and Δf H 0(Ca2Nb2O7, 298.15 K)= −3346.91 kJ mol−1.  相似文献   

2.
The low-temperature heat capacity C p,m of erythritol (C4H10O4, CAS 149-32-6) was precisely measured in the temperature range from 80 to 410 K by means of a small sample automated adiabatic calorimeter. A solid-liquid phase transition was found at T=390.254 K from the experimental C p-T curve. The molar enthalpy and entropy of this transition were determined to be 37.92±0.19 kJ mol−1 and 97.17±0.49 J K−1 mol−1, respectively. The thermodynamic functions [H T-H 298.15] and [S T-S 298.15], were derived from the heat capacity data in the temperature range of 80 to 410 K with an interval of 5 K. The standard molar enthalpy of combustion and the standard molar enthalpy of formation of the compound have been determined: Δc H m0(C4H10O4, cr)= −2102.90±1.56 kJ mol−1 and Δf H m0(C4H10O4, cr)= − 900.29±0.84 kJ mol−1, by means of a precision oxygen-bomb combustion calorimeter at T=298.15 K. DSC and TG measurements were performed to study the thermostability of the compound. The results were in agreement with those obtained from heat capacity measurements.  相似文献   

3.
The heat capacities (C p,m) of 2-amino-5-methylpyridine (AMP) were measured by a precision automated adiabatic calorimeter over the temperature range from 80 to 398 K. A solid-liquid phase transition was found in the range from 336 to 351 K with the peak heat capacity at 350.426 K. The melting temperature (T m), the molar enthalpy (Δfus H m0), and the molar entropy (Δfus S m0) of fusion were determined to be 350.431±0.018 K, 18.108 kJ mol−1 and 51.676 J K−1 mol−1, respectively. The mole fraction purity of the sample used was determined to be 0.99734 through the Van’t Hoff equation. The thermodynamic functions (H T-H 298.15 and S T-S 298.15) were calculated. The molar energy of combustion and the standard molar enthalpy of combustion were determined, ΔU c(C6H8N2,cr)= −3500.15±1.51 kJ mol−1 and Δc H m0 (C6H8N2,cr)= −3502.64±1.51 kJ mol−1, by means of a precision oxygen-bomb combustion calorimeter at T=298.15 K. The standard molar enthalpy of formation of the crystalline compound was derived, Δr H m0 (C6H8N2,cr)= −1.74±0.57 kJ mol−1.  相似文献   

4.
Low-temperature heat capacity of natural zinnwaldite was measured at temperatures from 6 to 303 K in a vacuum adiabatic calorimeter. An anomalous behavior of heat capacity function C p(T) has been revealed at very low temperatures, where this function does not tend to zero. Thermodynamic functions of zinnwaldite have been calculated from the experimental data. At 298.15 K, heat capacity C p(T) = 339.8 J K−1mol−1, calorimetric entropy S o(Т) – S o(6.08) = 329.1 J K−1 mol−1, and enthalpy Н o(Т) − Н o(6.08) = 54,000 J mol−1. Heat capacity and thermodynamic functions at 298.15 K for zinnwaldite having theoretical composition were estimated using additive method of calculation.  相似文献   

5.
Heat capacity C p(T) of the orthorhombic polymorph of L-cysteine was measured in the temperature range 6–300 K by adiabatic calorimetry; thermodynamic functions were calculated based on these measurements. At 298.15 K the values of heat capacity, C p; entropy, S m0(T)-S m0(0); difference in the enthalpy, H m0(T)-H m0(0), are equal, respectively, to 144.6±0.3 J K−1 mol−1, 169.0±0.4 J K−1 mol−1 and 24960±50 J mol−1. An anomaly of heat capacity near 70 K was registered as a small, 3–5% height, diffuse ‘jump’ accompanied by the substantial increase in the thermal relaxation time. The shape of the anomaly is sensitive to thermal pre-history of the sample.  相似文献   

6.
Rare-earth perchlorate complex coordinated with glycine [Nd2(Gly)6(H2O)4](ClO4)6·5H2O was synthesized and its structure was characterized by using thermogravimetric analysis (TG), differential thermal analysis (DTA), chemical analysis and elementary analysis. Its purity was 99.90%. Heat capacity measurement was carried out with a high-precision fully-automatic adiabatic calorimeter over the temperature range from 78 to 369 K. A solid-solid phase transformation peak was observed at 256.97 K, with the enthalpy and entropy of the phase transformation process are 4.438 kJ mol−1 and 17.270 J K−1 mol−1, respectively. There is a big dehydrated peak appears at 330 K, its decomposition temperature, decomposition enthalpy and entropy are 320.606 K, 41.364 kJ mol−1 and 129.018 J K−1 mol−1, respectively. The polynomial equations of heat capacity of this compound in different temperature ranges have been fitted. The standard enthalpy of formation was determined to be −8023.002 kJ mol−1 with isoperibol reaction calorimeter at 298.15 K.  相似文献   

7.
The heat capacity of a sample of Cs2CrO4 was determined in the temperature range 5 to 350 K by aneroid adiabatic calorimetry. The heat capacity at constant pressure Cpo(298.15 K), the entropy So(298.15 K), the enthalpy {Ho(298.15 K) - Ho(0)} and the function ? {Go(298.15 K) - Ho(0)}298.15K were found to be (146.06 ± 0.15) J K?1 mol?1, (228.59 ± 0.23) J K?1 mol?1, (30161 ± 30) J mol?1, and (127.43 ± 0.13) J K?1 mol?1, respectively. The heat capacity Cpo(298.15 K) and entropy So(298.15 K) and entropy So(298.15 K) of Rb2CrO4 are estimated to be (146.0 ± 1.0) J K?1 mol?1 and (217.6 ± 3.0) J K?1 mol?1, respectively.  相似文献   

8.
The molar heat capacities of the room temperature ionic liquid 1-butylpyridinium tetrafluoroborate (BPBF4) were measured by an adiabatic calorimeter in temperature range from 80 to 390 K. The dependence of the molar heat capacity on temperature is given as a function of the reduced temperature X by polynomial equations, C p,m [J K−1 mol−1]=181.43+51.297X −4.7816X 2−1.9734X 3+8.1048X 4+11.108X 5 [X=(T−135)/55] for the solid phase (80–190 K), C p,m [J K−1 mol−1]= 349.96+25.106X+9.1320X 2+19.368X 3+2.23X 4−8.8201X 5 [X=(T−225)/27] for the glass state (198–252 K), and C p,m[J K−1 mol−1]= 402.40+21.982X−3.0304X 2+3.6514X 3+3.4585X 4 [X=(T−338)/52] for the liquid phase (286–390 K), respectively. According to the polynomial equations and thermodynamic relationship, the values of thermodynamic function of the BPBF4 relative to 298.15 K were calculated in temperature range from 80 to 390 K with an interval of 5 K. The glass transition of BPBF4 was observed at 194.09 K, the enthalpy and entropy of the glass transition were determined to be ΔH g=2.157 kJ mol−1 and ΔS g=11.12 J K−1 mol−1, respectively. The result showed that the melting point of the BPBF4 is 279.79 K, the enthalpy and entropy of phase transition were calculated to be ΔH m = 8.453 kJ mol−1 and ΔS m=30.21 J K−1 mol−1. Using oxygen-bomb combustion calorimeter, the molar enthalpy of combustion of BPBF4 was determined to be Δc H m0 = −5451±3 kJ mol−1. The standard molar enthalpy of formation of BPBF4 was evaluated to be Δf H m0 = −1356.3±0.8 kJ mol−1 at T=298.150±0.001 K.  相似文献   

9.
The molar heat capacities of an aqueous Li2B4O7 solution were measured with a precision automated adiabatic calorimeter in the temperature range from 80 to 356 K at a concentration of 0.3492 mol⋅kg−1. The occurrence of a phase transition was determined based on the changes in the curve of the heat capacity with temperature. A phase transition was observed at 271.72 K corresponding to the solid-liquid phase transition; the enthalpy and entropy of the phase transition were evaluated to be Δ H m = 4.110 kJ⋅mol−1 and Δ S m = 15.13 J⋅K−1⋅mol−1, respectively. Using polynomial equations and thermodynamic relationship, the thermodynamic functions [H T H 298.15] and [S T S 298.15] of the aqueous Li2B4O7 solution relative to 298.15 K were calculated in temperature range 80 to 355 K at intervals of 5 K. Values of the relative apparent molar heat capacities of the aqueous Li2B4O7 solution, C p, were calculated at every 5 K in temperature range from 80 to 355 K from the experimental heat capacities of the solution and the heat capacities of pure water.  相似文献   

10.
The heat capacity and the enthalpy increments of strontium metaniobate SrNb2O6 were measured by the relaxation method (2-276 K), micro DSC calorimetry (260-320 K) and drop calorimetry (723-1472 K). Temperature dependence of the molar heat capacity in the form C pm=(200.47±5.51)+(0.02937±0.0760)T-(3.4728±0.3115)·106/T 2 J K−1 mol−1 (298-1500 K) was derived by the least-squares method from the experimental data. Furthermore, the standard molar entropy at 298.15 K S m0 (298.15 K)=173.88±0.39 J K−1 mol−1 was evaluated from the low temperature heat capacity measurements. The standard enthalpy of formation Δf H 0 (298.15 K)=-2826.78 kJ mol−1 was derived from total energies obtained by full potential LAPW electronic structure calculations within density functional theory.  相似文献   

11.
Temperature dependences of the heat capacities of disordered graphite-like nanostructures prepared by the thermobaric treatment of fullerite C60 (p = 2 and 8 GPa, T = 1373 K) were measured in the temperature ranges from 7 to 360 K in an adiabatic vacuum calorimeter and from 330 to 650 K in a differential scanning calorimeter. At T < 50 K, the dependences obtained were analyzed using the Debye theory of the heat capacity of solids and its multifractal version. The fractal dimensions D were determined and some conclusions on the heterodynamic character of the structures studied were made. The thermodynamic functions C p o T), H o(T) − H o(0), S o(T) − S o(0), and G o(T) − H o(0) were calculated in the temperature range from T → 0 to 610 (650) K. The thermodynamic properties of the graphite-like nanostructures studied and some carbon allotropes were compared. The standard entropies of formation Δf S o of the graphite nanostructures studied and diamond were calculated along with the standard entropies of the reactions of their synthesis from the face-centered cubic phase of fullerite C60 and their interconversions at T = 298.15 K. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1940–1945, September, 2008.  相似文献   

12.
The low-temperature heat capacity C p,m of sorbitol was precisely measured in the temperature range from 80 to 390 K by means of a small sample automated adiabatic calorimeter. A solid-liquid phase transition was found at T=369.157 K from the experimental C p-T curve. The dependence of heat capacity on the temperature was fitted to the following polynomial equations with least square method. In the temperature range of 80 to 355 K, C p,m/J K−1 mol−1=170.17+157.75x+128.03x 2-146.44x 3-335.66x 4+177.71x 5+306.15x 6, x= [(T/K)−217.5]/137.5. In the temperature range of 375 to 390 K, C p,m/J K−1 mol−1=518.13+3.2819x, x=[(T/K)-382.5]/7.5. The molar enthalpy and entropy of this transition were determined to be 30.35±0.15 kJ mol−1 and 82.22±0.41 J K−1 mol−1 respectively. The thermodynamic functions [H T-H 298.15] and [S T-S 298.15], were derived from the heat capacity data in the temperature range of 80 to 390 K with an interval of 5 K. DSC and TG measurements were performed to study the thermostability of the compound. The results were in agreement with those obtained from heat capacity measurements.  相似文献   

13.
The relative enthalpies, ΔHo (0) and ΔHo (298.15), of stationary points (four minimum and three transition structures) on the O3H potential energy surface were calculated with the aid of the G3MP2B3 as well as the CCSD(T)–CBS (W1U) procedures from which we earlier found mean absolute deviations (MAD) of 3.9 kJ mol−1 and 2.3 kJ mol−1, respectively, between experimental and calculated standard enthalpies of the formation of a set of 32 free radicals. For CCSD(T)-CBS (W1U) the well depth from O3 + H to trans-O3H, ΔHowell(298.15) = −339.1 kJ mol−1, as well as the reaction enthalpy of the overall reaction O3 + H→O2 + OH, ΔrHo(298.15) = −333.7 kJ mol−1, and the barrier of bond dissociation of trans-O3H → O2 + OH, ΔHo(298.15) = 22.3 kJ mol−1, affirm the stable short-lived intermediate O3H. In addition, for radicals cis-O3H and trans-O3H, the thermodynamic functions heat capacity Cop(T), entropy So (T), and thermal energy content Ho(T) − Ho(0) are tabulated in the range of 100 − 3000 K. The much debated calculated standard enthalpy of the formation of the trans-O3H resulted to be ΔfHo(298.15) = 31.1 kJ mol −1 and 32.9 kJ mol −1, at the G3MP2B3 and CCSD(T)-CBS (W1U) levels of theory, respectively. In addition, MR-ACPF-CBS calculations were applied to consider possible multiconfiguration effects and yield ΔfHo(298.15) = 21.2 kJ mol −1. The discrepancy between calculated values and the experimental value of −4.2 ± 21 kJ mol−1 is still unresolved. Note added in proof: Yu-Ran Luo and J. Alistair Kerr, based on the discussion in reference 12, recently presented an experimental value of ΔfHo(298.15) = 29.7 ± 8.4 kJ mol−1 in the 85th edition of the CRC Handbook of Chemistry and Physics (in progress).  相似文献   

14.
The temperature dependence of heat capacity of C70 fullerene was studied by calorimetry in the range between 6 and 390 K. Phase transitions were established and their thermodynamic characteristics were determined. From the experimental data obtained, the thermodynamic functionsH o (T)-H o(0),S o(T),G o(T)-H o(0) for temperatures between 0 and 390 K were calculated. The results were used to calculate the standard values of Δf S o, Δf G o, and logK f o for the formation of C70 from graphite. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 647–650, April, 1998.  相似文献   

15.
A solid complex Eu(C5H8NS2)3(C12H8N2) has been obtained from reaction of hydrous europium chloride with ammonium pyrrolidinedithiocarbamate (APDC) and 1,10-phenanthroline (o-phen⋅H2O) in absolute ethanol. IR spectrum of the complex indicated that Eu3+ in the complex coordinated with sulfur atoms from the APDC and nitrogen atoms from the o-phen. TG-DTG investigation provided the evidence that the title complex was decomposed into EuS. The enthalpy change of the reaction of formation of the complex in ethanol, Δr H m θ(l), as –22.214±0.081 kJ mol–1, and the molar heat capacity of the complex, c m, as 61.676±0.651 J mol–1 K–1, at 298.15 K were determined by an RD-496 III type microcalorimeter. The enthalpy change of the reaction of formation of the complex in solid, Δr H m θ(s), was calculated as 54.527±0.314 kJ mol–1 through a thermochemistry cycle. Based on the thermodynamics and kinetics on the reaction of formation of the complex in ethanol at different temperatures, fundamental parameters, including the activation enthalpy (ΔH θ), the activation entropy (ΔS θ), the activation free energy (ΔG θ), the apparent reaction rate constant (k), the apparent activation energy (E), the pre-exponential constant (A) and the reaction order (n), were obtained. The constant-volume combustion energy of the complex, Δc U, was determined as –16937.88±9.79 kJ mol–1 by an RBC-II type rotating-bomb calorimeter at 298.15 K. Its standard enthalpy of combustion, Δc H m θ, and standard enthalpy of formation, Δf H m θ, were calculated to be –16953.37±9.79 and –1708.23±10.69 kJ mol–1, respectively.  相似文献   

16.
The heat capacity of crystalline α-platinum dichloride was measured for the first time in the temperature intervals from 11 to 300 K (vacuum adiabatic microcalorimeter) and from 300 to 620 K (differential scanning calorimetry). In the 300–620 K temperature interval, the C° p values for α-PtCl2 (cr) coincide with the heat capacity of CrCl2 (cr) within the limits of experimental error, which made it possible to estimate the heat capacity of α-PtCl2 (cr) at higher temperatures. The approximating equation of the temperature dependence of the heat capacity in the interval from 298 to 900 K C° p (±0.8) = 63.5 + 21.4·10−3 T + 0.883·105/T 2 (J mol−1 K−1) was derived using the experimental values, as well as the literature data on the heat capacity of CrCl2 (cr). For the standard conditions, the C° p,298.15 and S°298.15 values are 70.92±0.08 and 100.9±0.33 J mol−1 K, respectively; H°298.15H°0 = 14 120±42 J mol−1. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1136–1138, June, 2008.  相似文献   

17.
Enthalpy of formation of the perovskite-related oxide BaCe0.9In0.1O2.95 has been determined at 298.15 K by solution calorimetry. Solution enthalpies of barium cerate doped with indium and mixture of BaCl2, CeCl3, InCl3 in ratio 1:0.9:0.1 have been measured in 1 M HCl with 0.1 M KI. The standard formation enthalpy of BaCe0.9In0.1O2.95 has been calculated as −1611.7±2.6 kJ mol−1. Room-temperature stability of this compound has been assessed in terms of parent binary oxides. The formation enthalpy of barium cerate doped by indium from the mixture of binary oxides is Δox H 0 (298.15 K)=−36.2±3.4 kJ mol−1.  相似文献   

18.
The molar heat capacities C p,m of 2,2-dimethyl-1,3-propanediol were measured in the temperature range from 78 to 410 K by means of a small sample automated adiabatic calorimeter. A solid-solid and a solid-liquid phase transitions were found at T-314.304 and 402.402 K, respectively, from the experimental C p-T curve. The molar enthalpies and entropies of these transitions were determined to be 14.78 kJ mol−1, 47.01 J K−1 mol for the solid-solid transition and 7.518 kJ mol−1, 18.68 J K−1 mol−1 for the solid-liquid transition, respectively. The dependence of heat capacity on the temperature was fitted to the following polynomial equations with least square method. In the temperature range of 80 to 310 K, C p,m/(J K−1 mol−1)=117.72+58.8022x+3.0964x 2+6.87363x 3−13.922x 4+9.8889x 5+16.195x 6; x=[(T/K)−195]/115. In the temperature range of 325 to 395 K, C p,m/(J K−1 mol−1)=290.74+22.767x−0.6247x 2−0.8716x 3−4.0159x 4−0.2878x 5+1.7244x 6; x=[(T/K)−360]/35. The thermodynamic functions H TH 298.15 and S TS 298.15, were derived from the heat capacity data in the temperature range of 80 to 410 K with an interval of 5 K. The thermostability of the compound was further tested by DSC and TG measurements. The results were in agreement with those obtained by adiabatic calorimetry.  相似文献   

19.
Relative enthalpies for low-and high-temperature modifications of Na3FeF6 and for the Na3FeF6 melt have been measured by drop calorimetry in the temperature range 723–1318 K. Enthalpy of modification transition at 920 K, δtrans H(Na3FeF6, 920 K) = (19 ± 3) kJ mol−1 and enthalpy of fusion at the temperature of fusion 1255 K, δfusH(Na3FeF6, 1255 K) = (89 ± 3) kJ mol−1 have been determined from the experimental data. Following heat capacities were obtained for the crystalline phases and for the melt, respectively: C p(Na3FeF6, cr, α) = (294 ± 14) J (mol K)−1, for 723 = T/K ≤ 920, C p(Na3FeF6, cr, β) = (300 ± 11) J (mol K)−1 for 920 ≤ T/K = 1233 and C p(Na3FeF6, melt) = (275 ± 22) J (mol K)−1 for 1258 ≤ T/K ≤ 1318. The obtained enthalpies indicate that melting of Na3FeF6 proceeds through a continuous series of temperature dependent equilibrium states, likely associated with the production of a solid solution.   相似文献   

20.
The temperature dependence of the heat capacity C p o = f(T) of palladium oxide PdO(cr.) was studied for the first time in an adiabatic vacuum calorimeter in the range of 6.48–328.86 K. Standard thermodynamic functions C p o(T), H o(T) — H o(0), S o(T), and G o(T) — H o(0) in the range of T → 0 to 330 K (key quantities in different thermodynamic calculations with the participation of palladium compounds) were calculated on the basis of the experimental data. Based on an analysis of studies on determining the thermodynamic properties of PdO(cr.), the following values of absolute entropy, standard enthalpy, and Gibbs function of the formation of palladium oxide are recommended: S o(298.15) = 39.58 ± 0.15 J/(K mol), Δf H o(298.15) = −112.69 ± 0.32 kJ/mol, Δf G o(298.15) = −82.68 ± 0.35 kJ/mol. The stability of Pd(OH)2 (amorph.) with respect to PdO(cr.) was estimated.  相似文献   

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