Heat capacities and thermodynamic properties of ammonium and potassium thiocyanates from 5 to 340 K

The heat capacities of ammonium and potassium thiocyanates were determined by adiabatic calorimetry over the range 5 to 340 K, and associated thermodynamic functions were computed from the results. At 298.15 K, the heat capacities Cp/cal K-1 mol-1 and entropies So/cal K-1 mol-1 are 29.98 and 33.52 for NH4SCN and 21.16 and 29.70 for KSCN. In both salts, the heat capacity contribution from libration of the thiocyanate ions may be represented by two Einstein functions up to 250 K. The torsional motion of the ammonium ion increases rapidly above 100 K and contributes more than 6 cal K-1 to the heat capacity above 250 K. Adjuvant data on potassium thiocyanate solutions lead to So = (34.23+/-0.3) cal K-1 mol-1 for SCN-(aq) at 298.15 K.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32848/1/0000224.pd

Succinic acid. Heat capacities and thermodynamic properties from 5 to 328 K. An efficient drying procedure

Heat capacities of succinic acid from 5 to 328 K were determined by adiabatic calorimetry. At 298.15 K, values of Cp, So, (Ho-H0o)/T and (Go-H0o)/T are 36.55, 39.99, 20.23, and -19.76 cal K-1 mol-1. No thermal anomalies were detected except that from a trace of occluded water at 272 K, found to be (0.0030 +/- 0.0005) per cent by analysis of the excess enthalpy absorption. Equilibration of pressed pellets for two days in a desiccator over Drierite proved to be an effective final drying technique.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32850/1/0000226.pd

The heat capacity and derived thermophysical properties of In2O3 from 0 to 1000 K

The heat capacity from 5 to 350K of In2O3 has been measured by adiabatic calorimetry. For the thermophysical properties at room temperature Cop(298.15 K) = (99.08 +/- 0.09) J mol -1 K -1 and So(298.15 K) = (101.80 +/- 0.06) J mol-1 K-1 have been derived. Enthalpy increments relative to 298.15 K have been measured by drop calorimetry from 502 to 959.2 K: [Ho(T)-Ho(298.15 K)}/J mol-1=109.1383(T/K)+13.73786 x 10-3(T/K)2 +16.22947 x 105(T/K)-1-39,204.2.The thermodynamic functions, including the formation properties [Delta]fHo and [Delta]fGo(T), have been derived for temperatures up to 1000K.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30191/1/0000576.pd

Uranium Monosulfide. The Ferromagnetic Transition. The Heat Capacity and Thermodynamic Properties from 1.5° to 350°K

The heat capacity of uranium monosulfide was measured from 1.5° to 22°K by an isothermal (isoperibol) method and from 6° to 350°K by an adiabatic technique. The ferromagnetic transition at 180.1°K has a characteristic lambda shape and associated magnetic ordering entropy and enthalpy increments of 1.62 ± 0.2 cal °K−1mole−1 and 231 ± 20 cal mole−1, respectively, over the temperature range 0° to 230°K. The correlation of the thermal data with magnetic studies is discussed. The heat capacity below 9°K is represented by Cp  =  5.588 × 10−3T + 2.627 × 10−4T3 / 2 + 6.752 × 10−5T3cal°K−1mole−1Cp=5.588×10−3T+2.627×10−4T3∕2+6.752×10−5T3cal°K−1mole−1, in which the successive terms represent conduction electronic, magnetic, and lattice contributions. Values of the entropy [S°], enthaply function [(H° − H°0) / T][(H°−H°0)∕T], and Gibbs‐energy function [(G° − H°0) / T][(G°−H°0)∕T] are 18.64 ± 0.005, 8.94 ± 0.002, and − 9.70 ± 0.02 cal °K−1 mole−1, respectively, at 298.15°K. The Gibbs energy of formation at 298.15°K is − 72.9 ± 3.5 kcal mole−1.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/70623/2/JCPSA6-48-1-155-1.pd

The thermodynamics of ammonium scheelites. III. An analysis of the heat capacity and related data of deuterated ammonium perrhenate ND4ReO4

An analysis of the heat capacity of deuterated and undeuterated NH4ReO4 has been carried out in which the effects of the anisotropy of the thermal expansion have been considered, an approach hitherto not used for ammonium compounds. In the ammonium scheelites, the axial thermal expansion coefficients are very large, but of opposite sign, and as a result the volume of the scheelite lattice is nearly independent of temperature. It is shown that the correction from constant stress to constant strain results in a major contribution to the heat capacity of this highly anisotropic lattice. The difference between the experimental and calculated values of heat capacity, referred to as ΔCp, is expressed as the sum of the contributions from the anisotropy and the rotational heat capacity. The results of the analysis show that the rotational contribution is much smaller then previously thought. However, the exact contribution of the anisotropy cannot be calculated at this time because the elastic constants are not known. In calculating the heat capacity, maximum use has been made of external optical mode frequencies derived from spectroscopic measurements.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71156/2/JCPSA6-85-10-5963-1.pd

The thermodynamics of the divalent metal fluorides. II. Heat capacity of the fast ion conductor BaSnF 4 from 7 to 345 K

The heat capacity of the fast ion conductor BaSnF 4 was measured over the temperature range 7< T <345 K using adiabatic calorimetry. Our results show that a phase transition is not present. However, an anomalous rise in the molar heat capacity, C p,m , occurs in the region 210< T <310 K; the entropy change of this rise amounts to ΔS/R =0.112. This anomaly coincides with the temperature range where a break in the slope of the electrical conductivity has been observed, which results in a threefold decrease in the activation energy required in the temperature region above the break at 272 K. Standard molar thermodynamic functions are presented at selected temperatures from 5 to 345 K.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44570/1/10765_2005_Article_BF01133276.pd

Thermophysical properties of the lanthanide sesquisulfides. III. Determination of Schottky and lattice heat‐capacity contributions of γ‐phase Sm2S3 and evaluation of the thermophysical properties of the γ‐phase Ln2S3 subset

We report the experimental heat capacity of γ‐phase Sm2S3 and derived thermophysical properties at selected temperatures. The entropy, enthalpy increments, and Gibbs energy function are 21.50R, 3063R⋅K, and 11.23R at 298.15 K. The experimental heat capacity is made up of lattice and electronic (Schottky) contributions. The lattice contribution is determined for all γ‐phase lanthanide sesquisulfides (Ln2S3 ) using the Komada/Westrum model. The difference between the experimental heat capacity and the deduced lattice heat capacity is analyzed as the Schottky contribution. Comparisons are made between the calorimetric Schottky contributions and those determined based on crystal‐field electronic energy levels of Ln3+ ions in the lattice and between the Schottky contributions obtained from the empirical volumetric priority approach and from the Komada/Westrum theoretical approach. Predictions for the thermophysical properties of γ‐phase Eu2S3 and γ‐phase Pm2S3 (unavailable for experimental determination) are also presented.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/71137/2/JCPSA6-96-8-6149-1.pd

The heat capacity and derived thermophysical properties of some alkaline earth silicates and zirconates from 5 to 1000 K--I. Crystalline SrSiO3 and Sr2SiO4

The heat capacities of SrSO3 and Sr2SiO4 were measured from 5 to 350 K. by adiabatic calorimetry, and the derived thermophysical properties, H[deg], S[deg], and {G[deg] - H[deg] (0)}/T were calculated. For the standard molar entropies at 298.15 K the values (95.65 +/- 0.21) J mol-1 K-1 and (155.44 +/- 0.25) J mol-1 K-1, respectively were found, Enthalpy increments relative to 298.15 K were measured by drop calorimetry for SrSiO3 from 503.0 to 886.4 K and for Sr2SiO4 from 503.0 to 886.2 K.The thermodynamic functions including the formation properties [Delta]HT[deg](t) and [delta]DG[deg](T), were derived for temperatures up to 1000 K.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30026/1/0000394.pd

Low-temperature heat capacity and thermodynamic functions of IrO2

The heat capacity from 5 to 350 K of IrO2 has been measured by quasi-adiabatic equilibrium calorimetry. The values for the thermodynamic properties at 298.15 K have been calculated as Cp, m(T)/R = 6.687, [Delta]0TSmo/R = 6.133, [Delta]0THmo/(R [middle dot] K) = 1039.5, and [Phi]mo(T, 0)/R = 2.647. The low-temperature heat capacity shows typical metallic behavior with an electronic coefficient [gamma]/R = 0.00067 K-1. The entropy at 298.15 K is shown to be consistent with the volumetric dependence of this quantity.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/27003/1/0000570.pd