共查询到20条相似文献,搜索用时 15 毫秒
1.
《The Journal of chemical thermodynamics》2004,36(5):349-357
The molar heat capacity of Zn2GeO4, a material which exhibits negative thermal expansion below ambient temperatures, has been measured in the temperature range 0.5⩽(T/K)⩽400. At T=298.15 K, the standard molar heat capacity is (131.86 ± 0.26) J · K−1 · mol−1. Thermodynamic functions have been generated from smoothed fits of the experimental results. The standard molar entropy at T=298.15 K is (145.12 ± 0.29) J · K−1 · mol−1. The existence of low-energy modes is supported by the excess heat capacity in Zn2GeO4 compared to the sums of the constituent binary oxides. 相似文献
2.
Jiří Málek Takefumi Mitsuhashi Naoki Ohashi Yuki Taniguchi Hitoshi Kawaji Tooru Atake 《The Journal of chemical thermodynamics》2011,43(3):405-409
The heat capacity of polycrystalline germanium disulfide α-GeS2 has been measured by relaxation calorimetry, adiabatic calorimetry, DSC and heat flux calorimetry from T = (2 to 1240) K. Values of the molar heat capacity, standard molar entropy and standard molar enthalpy are 66.191 J · K?1 · mol?1, 87.935 J · K?1 · mol?1 and 12.642 kJ · mol?1. The temperature of fusion and its enthalpy change are 1116 K and 23 kJ · mol?1, respectively. The thermodynamic functions of α-GeS2 were calculated over the range (0 ? T/K ? 1250). 相似文献
3.
Quan Shi Claine L. Snow Juliana Boerio-Goates Brian F. Woodfield 《The Journal of chemical thermodynamics》2010,42(9):1107-1115
We have evaluated the accuracy of the heat capacity option of a Quantum Design physical property measurement system (PPMS) by measuring the heat capacity of various types of conducting and insulating samples over the temperature range from (2 to 300) K. In particular, the accuracy of measurements on a copper pellet was determined to be ±2% for 2 K < T < 20 K and ±0.6% for 20 K < T < 300 K, however similar measurements on a powdered sample of benzoic acid had errors as high as 20%. A new method for heat capacity measurements of powdered samples using a PPMS system has been developed that allows us to obtain heat capacity measurements for both insulating and conducting powdered samples with an accuracy of ±1% from (20 to 300) K and ±2% to ±5% for T < 20 K. Since the heat capacity of substances (and corresponding entropy contribution) is small at low temperatures for lattice-only contributions, the accuracy of ±2% to ±5% below 20 K is considered acceptable. As a test of the new method, the heat capacity of powdered bulk hematite has been measured in the temperature range from (2 to 300) K with the PPMS, and its standard entropy at T = 298.15 K was calculated to be (87.33 and 87.27) J · K?1 · mol?1, which deviates ?0.08% and ?0.15% from the accepted reference value, respectively. We recommend that this new method become the standard for accurate heat capacity measurements on insulating powdered samples using a PPMS system and the corresponding thermodynamic calculations. 相似文献
4.
《The Journal of chemical thermodynamics》2004,36(5):359-375
The molar heat capacities of GeCo2O4 and GeNi2O4, two geometrically frustrated spinels, have been measured in the temperature range from T=(0.5 to 400) K. Anomalies associated with magnetic ordering occur in the heat capacities of both compounds. The transition in GeCo2O4 occurs at T=20.6 K while two peaks are found in the heat capacity of GeNi2O4, both within the narrow temperature range between 11.4<(T/K)<12.2. Thermodynamic functions have been generated from smoothed fits of the experimental results. At T=298.15 K the standard molar heat capacities are (143.44 ± 0.14) J · K−1 · mol−1 for GeCo2O4 and (130.76 ± 0.13) J · K−1 · mol−1 for GeNi2O4. The standard molar entropies at T=298.15 K for GeCo2O4 and GeNi2O4 are (149.20 ± 0.60) J · K−1 · mol−1 and (131.80 ± 0.53) J · K−1 · mol−1 respectively. Above 100 K, the heat capacity of the cobalt compound is significantly higher than that of the nickel compound. The excess heat capacity can be reasonably modeled by the assumption of a Schottky contribution arising from the thermal excitation of electronic states associated with the CO2+ ion in a cubic crystal field. The splittings obtained, 230 cm−1 for the four-fold-degenerate first excited state and 610 cm−1 for the six-fold degenerate second excited state, are significantly lower than those observed in pure CoO. 相似文献
5.
C.A. Alexander J.S. Ogden S.M. Risser Van E. Wood 《The Journal of chemical thermodynamics》2009,41(5):610-616
Thermodynamic properties of the high-stability intermetallic compound nickel aluminide, NiAl, have been determined from mass-spectrometric, weight-loss effusion, and calorimetric measurements, using samples from a single preparation with a composition determined to be Ni0.986Al1.014. Per mole of NiAl molecules, the specific heat capacity at room temperature of 298 K is 48.54 J · K?1 · mol?1, with a linear temperature dependence of +0.0104 J · K?2 · mol?1. At the same temperature, the enthalpy of formation is ?133.7 kJ · mol?1, the entropy is about 53.8 J · K?1 · mol?1 and the enthalpy difference between room temperature and absolute zero is 7.97 kJ · mol?1. The Gibbs free-energy is ?130.2 kJ · mol?1 at T = 298 K, with a linear temperature dependence of +5.04 J · K?1 · mol?1. The Debye temperature is 452 K, while the electronic density-of-states at the Fermi-level is about 0.29 states per eV-atom. The NiAl+ ions were observed in the high-temperature mass spectra. Pressures for the gas at these temperatures were estimated and used with the results of quantum-mechanical calculations of total energy, specific heat, and entropy to calculate free-energy functions for the gas. These and additional results are compared with other measurements and discussed in terms of current theories of the electronic and structural properties of the compound. 相似文献
6.
The low temperature heat capacity of the ZnO–CoO solid solution system was measured from 2 to 300 K using the heat capacity option of a Quantum Design Physical Property Measurement System (PPMS). The thermodynamic functions in this temperature range were derived by curve fitting. The standard entropies of bulk ZnO and bulk ZnO–CoO (wurtzite, 18 mol% CoO) at T = 298.15 K were calculated to be (43.1 ± 0.4) J · mol−1 · K−1 and (45.2 ± 0.5) J · mol−1 · K−1, respectively. The surface entropy of ZnO was evaluated to be (0.02 ± 0.01) mJ · K−1 · m−2, which is essentially zero. No sharp magnetic transitions were observed in the solid solution samples. The nanophase solid solution, 12 mol% CoO, appears to bind H2O on its surface more strongly than ZnO. 相似文献
7.
《The Journal of chemical thermodynamics》2004,36(5):393-399
Heat capacities of 2,4-dichlorobenzaldehyde have been measured with a high-precision automatic adiabatic calorimeter over the temperature range from (79 to 371) K. The melting temperature, molar enthalpy, and entropy of fusion were determined by the heat capacity measurements to be (347.24 ± 0.13) K, (20468 ± 19) J · mol−1, and (58.94 ± 0.04) J · K−1 · mol−1, respectively. The melting temperatures for the sample and the absolutely pure compound have been obtained from fractional melting experiments to be (347.230 and 347.619) K, respectively, and the chemical purity of the sample was calculated to be 0.9921 mol fraction according to the Van't Hoff equation. Moreover, the solid-to-liquid phase transition of the substance was further investigated by using DSC technique. The results obtained from the heat capacity measurements were in agreement with those from the DSC analysis. 相似文献
8.
The low-temperature heat capacity of NiAl2O4 and CoAl2O4 was measured between T = (4 and 400) K and thermodynamic functions were derived from the results. The measured heat-capacity curves show sharp anomalies peaking at around T = 7.5 K for NiAl2O4 and at T = 9 K for CoAl2O4. The exact cause of these anomalies is unknown. From our results, we suggest a standard entropy for NiAl2O4 at T = 298.15 K of (97.1 ± 0.2) J · mol?1 · K?1 and for CoAl2O4 of (100.3 ± 0.2) J · mol?1 · K?1. 相似文献
9.
A new Mn (III) Schiff-base coordination compound, [Mn(L)(NCS)]2 (H2L = N,N′-bis(5-chlorosalicylidene)-1,2-diaminoethane), has been synthesized and characterized structurally and magnetically. The target compound is a phenoxo-bridged dimeric compound with the isothiocyanate coordinating in a usual bent mode. A magnetic susceptibility study reveals that the target compound exhibits antiferromagnetic intra-dimer coupling between Mn (III) ions. The low temperature heat capacity of the compound over the temperature range (2 to 300) K has been measured using the heat capacity option of a Quantum Design Physical Property Measurement System (PPMS). The thermodynamic functions in the experimental temperature range have been determined by curve fitting. The standard entropy and enthalpy of the as-prepared compound at T = 298.15 K have been calculated to be (924.52 ± 10.17) J · K−1 · mol−1 and (133.47 ± 1.47) kJ · mol−1, respectively. 相似文献
10.
Drew Gorman-Lewis Jeremy B. Fein Peter C. Burns Jennifer E.S. Szymanowski Jenalee Converse 《The Journal of chemical thermodynamics》2008,40(6):980-990
The mobility of uranium under oxidizing conditions can only be modeled if the thermodynamic stabilities of the secondary uranyl minerals are known. Toward this end, we synthesized metaschoepite (UO3(H2O)2), becquerelite (Ca(UO2)6O4(OH)6(H2O)8), compreignacite (K2(UO2)6O4(OH)6(H2O)7), sodium compreignacite (Na2(UO2)6O4(OH)6(H2O)7), and clarkeite (Na(UO2)O(OH)) and performed solubility measurements from both undersaturation and supersaturation under controlled-pH conditions. The solubility measurements rigorously constrain the values of the solubility products for these synthetic phases, and consequently the standard-state Gibbs free energies of formation of the phases. The calculated lg solubility product values (lg Ksp), with associated 1σ uncertainties, for metaschoepite, becquerelite, compreignacite, sodium compreignacite, and clarkeite are (5.6 ?0.2/+0.1), (40.5 ?1.4/+0.2), (35.8 ?0.5/+0.3), (39.4 ?1.1/+0.7), and (9.4 ?0.9/+0.6), respectively. The standard-state Gibbs free energies of formation, with their 2σ uncertainties, for these same phases are (?1632.2 ± 7.4) kJ · mol?1, (?10305.6 ± 26.5) kJ · mol?1, (?10107.3 ± 21.8) kJ · mol?1, (?10045.6 ±24.5) kJ · mol?1, and (?1635.1 ± 23.4) kJ · mol?1, respectively. Combining our data with previously measured standard-state enthalpies of formation for metaschoepite, becquerelite, sodium compreignacite, and clarkeite yields calculated standard-state entropies of formation, with associated 2σ uncertainties, of (?532.5 ± 8.1) J · mol?1 · K?1, (?3634.5 ± 29.7) J · mol?1 · K?1, ( ?2987.6 ± 28.5) J · mol?1 · K?1, and (?300.5 ± 23.9) J · mol?1 · K?1, respectively. The measurements and associated calculated thermodynamic properties from this study not only describe the stability and solubility at T = 298 K, but also can be used in predictions of uranium mobility through extrapolation of these properties to temperatures and pressures of geologic and environmental interest. 相似文献
11.
《The Journal of chemical thermodynamics》2007,39(1):108-114
The constant-volume energy of combustion of crystalline anhydrous caffeine (C8H10N4O2) in α (lower temperature steady) crystal form was measured by a bomb combustion calorimeter, the standard molar enthalpy of combustion of caffeine at T = 298.15 K was determined to be −(4255.08 ± 4.30) kJ · mol−1, and the standard molar enthalpy of formation was derived as −(322.15 ± 4.80) kJ · mol−1. The heat capacity of caffeine in the same crystal form was measured in the temperature range from (80 to 387) K by an adiabatic calorimeter. No phase transition or thermal anomaly was observed in the above temperature range. The thermal behavior of the compound was further examined by thermogravimetry (TG), differential thermal analysis (DTA) over the range from (300 to 700) K and by differential scanning calorimetry (DSC) over the range from (300 to 540) K, respectively. From the above thermal analysis a (solid–solid) and a (solid–liquid) phase transition of the compound were found at T = (413.39 and 509.00) K, respectively; and the corresponding molar enthalpies of these transitions were determined to be (3.43 ± 0.02) kJ · mol−1for the (solid–solid) transition, and (19.86 ± 0.03) kJ · mol−1 for the (solid–liquid) transition, respectively. 相似文献
12.
《The Journal of chemical thermodynamics》2006,38(3):211-223
The high-temperature heat capacity of zirconia was directly measured by differential scanning calorimetry between T = (1050 and 1700) K and derived from the heat content measured by transposed temperature drop calorimetry between T = (970 and 1770) K, including the monoclinic–tetragonal (m–t) phase transition region. The enthalpy and entropy of the m–t phase transition are (5.43 ± 0.31) kJ · mol−1 and (3.69 ± 0.21) J · K−1 · mol−1, respectively. Values of thermodynamic functions are provided from room temperature to 2000 K. 相似文献
13.
《The Journal of chemical thermodynamics》2003,35(3):475-492
Low-temperature calorimetric measurements have been performed on DyBr3(s) in the temperature range (5.5 to 420 K ) and on DyI3(s) from T=4 K to T=420 K. The data reveal enhanced heat capacities below T=10 K, consisting of a magnetic and an electronic contribution. From the experimental data on DyBr3(s) a C0p,m (298.15 K) of (102.2±0.2) J·K−1·mol−1 and a value for {S0m (298.15 K) − S0m (5.5 K)} of (205.5±0.5) J·K−1·mol−1, have been obtained. For DyI3(s), {S0m (298.15 K) − S0m (4 K)} and C0p,m (298.15 K) have been determined as (226.9±0.5) J·K−1·mol−1 and (103.4±0.2) J·K−1·mol−1, respectively. The values for {S0m (5.5 K) − S0m (0)} for DyBr3(s) and {S0m (4 K) − S0m (0)} for DyI3(s) have been calculated, giving S0m (298.15 K)=(212.3±0.9) J·K−1·mol−1 in case of DyBr3(s) and S0m (298.15 K) =(233.1±0.7) J·K−1·mol−1 for DyI3(s). The high-temperature enthalpy increment has been measured for DyBr3(s) in the temperature range (525 to 799 K) and for DyI3(s) in the temperature range (525 to 627 K). From the results obtained and enthalpies of formation from the literature, thermodynamic functions for DyBr3(s) and DyI3(s) have been calculated from T→0 to their melting temperatures at 1151.0 K and 1251.5 K, respectively. 相似文献
14.
Hydroboration reactions of 4-octene with HBBr2 · SMe2, HBCl2 · SMe2 and H2BBr · SMe2 in CH2Cl2 were studied as function of concentration and temperature and compared with those of 1-octene. On average, hydroboration with dihaloborane proceeded 16 times slower for 4-octene than for 1-octene. In the case of the reactions with the monohaloborane, this factor is halved. This can be explained by the difference in the relative rates of dissociates of Me2S from the dihaloborane and a monohaloborane complex, respectively. The reactions involving H2BBr · SMe2 also exhibited a k?2 value, an indication of the presence of a parallel reaction, most likely a rearrangement process facilitating isomerization by way of a π-complex. The moderate ΔH≠ values accompanied by small ΔS≠ values (94 ± 4 kJ mol?1, ?3 ± 13 J K?1 mol?1 for HBBr2 · SMe2; 93 ± 1 kJ mol?1, ?17 ± 4 J K?1 mol?1 for HBCl2 · SMe2 and in the case of H2BBr · SMe2, 90 ± 13 kJ mol?1, +12 ± 44 J K?1 mol?1 and 83 ± 13 kJ mol?1, ?24 ± 45 J K?1 mol?1, respectively, for the k2 and k?2 processes) imply a process that is dissociatively dominated, with the overall mode of activation being interchange dissociative (Id). 相似文献
15.
《The Journal of chemical thermodynamics》2004,36(10):895-899
Low-temperature heat capacities of pyrimethanil laurate (C24H37N3O2) were precisely measured with an automated adiabatic calorimeter over the temperature range between T = 78 K and T = 340 K. The sample was observed to melt at (321.52 ± 0.04) K. The molar enthalpy and entropy of fusion as well as the chemical purity of the compound were determined to be (67244 ± 11) J · mol−1, (209.28 ± 0.02) J · mol−1 · K−1, (0.9943 ± 0.0004) mass fraction, respectively. The extrapolated melting temperature for the absolutely pure compound obtained from fractional melting experiments was (322.264 ± 0.006) K. 相似文献
16.
The enthalpy of formation of zinc acetate dihydrate (Zn(CH3COO)2 · 2H2O) was measured with respect to crystalline zinc oxide (ZnO), glacial acetic acid (CH3COOH) and liquid water by room temperature solution calorimetry. The enthalpy of formation was verified by utilizing two independent thermodynamic cycles, using enthalpy of solution measurements in 5 mol · L?1 sodium hydroxide (NaOH) and in 5 mol · L?1 hydrochloric acid (HCl) solutions. The enthalpy of the reaction ZnO (cr) + 2CH3COOH (l) + H2O (l) to form Zn(CH3COO)2 · 2H2O (cr) is –(65.78 ± 0.36) kJ · mol?1 for measurements in 5 mol · L?1 NaOH and –(66.25 ± 0.17) kJ · mol?1 for measurements in 5 mol · L?1 HCl. The standard enthalpy of formation of Zn(CH3COO)2 · 2H2O from the elements is –(1669.35 ± 1.30) kJ · mol?1. This work provides the first calorimetric measurement of the enthalpy of formation of Zn(CH3COO)2 · 2H2O. 相似文献
17.
Claine L. Snow Quan Shi Juliana Boerio-Goates Brian F. Woodfield 《The Journal of chemical thermodynamics》2010,42(9):1136-1141
The constant pressure heat capacity of a bulk hematite powder was measured using a Quantum Design physical properties measurement system (PPMS). The results of two series showed good precision and agreed well with measurements reported by Westrum and Grønvold. The standard molar entropy at T = 298.15 K was calculated to be (87.32 ± 2) J · mol?1 · K?1 for Series 1 and (87.27 ± 2) J · mol?1 · K?1 for Series 2, which are in good agreement with the value of (87.40 ± 0.2) J · mol?1 · K?1 (originally 20.889 cal · deg?1 · mole?1) calculated by Westrum and Grønvold. No anomaly was observed for the Morin transition, and theoretical fits below T = 15 K required a ferromagnetic T3/2 term. 相似文献
18.
Two pure hydrated lead borates, Pb(BO2)2·H2O and PbB4O7·4H2O, have been characterized by XRD, FT-IR, DTA-TG techniques and chemical analysis. The molar enthalpies of solution of Pb(BO2)2·H2O and PbB4O7·4H2O in 1 mol dm?3 HNO3(aq) were measured to be (?35.00 ± 0.18) kJ mol?1 and (35.37 ± 0.14) kJ mol?1, respectively. The molar enthalpy of solution of H3BO3(s) in 1 mol dm?3 HNO3(aq) was measured to be (21.19 ± 0.18) kJ mol?1. The molar enthalpy of solution of PbO(s) in (HNO3 + H3BO3)(aq) was measured to be ?(61.84 ± 0.10) kJ mol?1. From these data and with incorporation of the enthalpies of formation of PbO(s), H3BO3(s) and H2O(l), the standard molar enthalpies of formation of ?(1820.5 ± 1.8) kJ mol?1 for Pb(BO2)2·H2O and ?(4038.1 ± 3.4) kJ mol?1 for PbB4O7·4H2O were obtained on the basis of the appropriate thermochemical cycles. 相似文献
19.
《The Journal of chemical thermodynamics》2003,35(9):1469-1487
Standard values of Gibbs free energy, entropy, and enthalpy of Na2Ti6O13 and Na2Ti3O7 were determined by evaluating emf-measurements of thermodynamically defined solid state electrochemical cells based on a Na–β″-alumina electrolyte. The central part of the anodic half cell consisted of Na2CO3, while two appropriate coexisting phases of the ternary system Na–Ti–O are used as cathodic materials. The cell was placed in an atmosphere containing CO2 and O2. By combining the results of emf-measurements in the temperature range of 573⩽T/K⩽1023 and of adiabatic calorimetric measurements of the heat capacities in the low-temperature region 15⩽T/K⩽300, the thermodynamic data were determined for a wide temperature range of 15⩽T/K⩽1100. The standard molar enthalpy of formation and standard molar entropy at T=298.15 K as determined by emf-measurements are ΔfHm0=(−6277.9±6.5) kJ · mol−1 and Sm0=(404.6±5.3) J · mol−1 · K−1 for Na2Ti6O13 and ΔfHm0=(−3459.2±3.8) kJ · mol−1 and Sm0=(227.8±3.7) J · mol−1 · K−1 for Na2Ti3O7. The standard molar entropy at T=298.15 K obtained from low-temperature calorimetry is Sm0=399.7 J · mol−1 · K−1 and Sm0=229.4 J · mol−1 · K−1 for Na2Ti6O13 and Na2Ti3O7, respectively. The phase widths with respect to Na2O content were studied by using a Na2O-titration technique. 相似文献
20.
《The Journal of chemical thermodynamics》2004,36(2):79-86
Low-temperature heat capacities of the 9-fluorenemethanol (C14H12O) have been precisely measured with a small sample automatic adiabatic calorimeter over the temperature range between T=78 K and T=390 K. The solid–liquid phase transition of the compound has been observed to be Tfus=(376.567±0.012) K from the heat-capacity measurements. The molar enthalpy and entropy of the melting of the substance were determined to be ΔfusHm=(26.273±0.013) kJ · mol−1 and ΔfusSm=(69.770±0.035) J · K−1 · mol−1. The experimental values of molar heat capacities in solid and liquid regions have been fitted to two polynomial equations by the least squares method. The constant-volume energy and standard molar enthalpy of combustion of the compound have been determined, ΔcU(C14H12O, s)=−(7125.56 ± 4.62) kJ · mol−1 and ΔcHm∘(C14H12O, s)=−(7131.76 ± 4.62) kJ · mol−1, by means of a homemade precision oxygen-bomb combustion calorimeter at T=(298.15±0.001) K. The standard molar enthalpy of formation of the compound has been derived, ΔfHm∘(C14H12O,s)=−(92.36 ± 0.97) kJ · mol−1, from the standard molar enthalpy of combustion of the compound in combination with other auxiliary thermodynamic quantities through a Hess thermochemical cycle. 相似文献