Gerald K. Johnson

The enthalpies of solution and neutralization of HF(I); enthalpies of dilution and derived thermodynamic properties of HF(aq)

Enthalpies of solution, ΔHsoln, of HF(I) in water and the enthalpy of neutralization, ΔHN, of HF(I) in dilute NaOH, as well as some enthalpies of dilution, ΔHdlln, of HF(aq) were measured in a reaction calorimeter. These results were combined with some enthalpies of dilution of HF(aq) reported in the literature to obtain the enthalpy of solution of liquid HF as a function of composition between HF·∞H2O and HF·H2O. The enthalpies of formation of all aqueous HF solutions in this concentration range were obtained by combination of the enthalpy of formation of HF(I) and the enthalpies of solution of HF(I). In addition, the relative apparent molar enthalpies, Lo, of HF(aq) and the relative partial molar enthalpies, L2 and L1, of HF and H2O, respectively, were calculated. Some of the key measured and derived results at 298.15 K obtained in this work are ΔHoN(HF, 1) = - (21017 ± 29) calth mol−1, ΔHosoln(HF, 1) = − (7672 ± 38) calth mol−1, and ΔHot,(HF, aq) = ΔHof(F−, aq) = − (80.22 ± 0.07) kcalth mol−1.

Thermodynamic studies of zeolites: clinoptilolite

Calorimetric studies are described of a carefully characterized specimen of clinoptilolite (Malheur County, Oregon, U.S.A.) of composition: S r 0.036 M g 0.124 C a 0.761 M n 0.002 B a 0.062 K 0.543 N a 0.954 A l 3.450 F e 0.017 S i 14.533 O 36.000 ⋅ 10.922 H 2 O . Values are reported of the standard molar enthalpies of formation ΔfHom at 298.15 K and of the standard molar enthalpy increments {Hom(T) − Hom(298.15 K)} for both clinoptilolite and dehydrated clinoptilolite, as well as the low-temperature molar heat capacity Cop,m and, by derivation, the standard molar entropy increment {Som(T) − Som(0)} for clinoptilolite alone. The conventional thermodynamic properties have been calculated for both compounds.

Lithium nitride (Li3N): standard enthalpy of formation by solution calorimetry

Abstract The enthalpies of reaction of a carefully prepared and characterized specimen of lithium nitride, Li 3 N, with H 2 O and with HCl(aq) were found to be −(581.62±1.42) kJ mol −1 [−(139.01±0.34) kcal th mol −1 ] and −(803.50±1.26) kJ mol −1 [−(192.04±0.30) kcal th mol −1 ], respectively. Enthalpies of solution of LiCl and NH 4 Cl were also measured. Combination of the measured results with auxiliary thermochemical data from the literature yielded values of −(165.14±1.55) kJ mol −1 [−(39.47±0.37) kcal th mol −1 ] and −(164.77±1.51) kJ mol −1 [−(39.38±0.36) kcal th mol −1 ], respectively, for the standard enthalpy of formation, ΔH f o (Li 3 N, c, 298.15 K). A weighted mean value, −(164.93±1.09) kJ mol −1 [−(39.42±0.26) kcal th mol −1 ], is recommended for ΔH f o (Li 3 N, c, 298.15 K). This result differs by about 8 kcal th mol −1 from previous determinations.

Thermodynamics of the lanthanide trifluorides. I. The heat capacity of lanthanum trifluoride, LaF3 from 5 to 350°K and enthalpies from 298 to 1477°K

The heat capacity of a sample of LaF3 was determined in the temperature range 5–350°K by aneroid adiabatic calorimetry and the enthalpy from 298.15 to 1477°K by drop calorimetry. The heat capacity at constant pressure C°p(298.15°K), the entropy S° (298.15°K), the enthalpy [H° (298.15°K)−H° (0)] and the Planck function −[G° (298.15°K)−H° (0)]/298.15°K; were found to be (90.29±0.09) J °K−1⋅mole−1, (106.98±0.11) J °K−1⋅mole−1, (16717±17) J mole−1, and (50.91±0.05) J °K−1⋅mole−1. The thermal functions from the present research were extended up to the melting temperature (1766°K) by combination with previously published results. The anomalously high heat capacity from about 1100 to 1766°K is discussed.

The enthalpies of formation of XeF6(c), XeF4(c), XeF2(c), and PF3(g)☆☆☆

Abstract The energies of reaction of XeF6(c), XeF4(c), and XeF2(c) with PF3(g) were measured in a bomb calorimeter. These results were combined with the enthalpy of fluorination of PF3(g), which was redetermined to be −(151.98 ± 0.07) kcalth mol−1, to derive (at 298.15 K) ΔHfo(XeF6, c, I) = −(80.82 ± 0.53) kcalth mol−1, ΔHfo(XeF4, c) = −(63.84 ± 0.21) kcalth mol−1, and ΔHfo(XeF2, c) = −(38.90 ± 0.21) kcalth mol−1. The enthalpies of formation of the solid xenon fluorides were combined with reported enthalpies of sublimation to derive (at 298.15 K) ΔHfo(XeF6, g) = −(66.69 ± 0.61) kcalth mol−1, ΔHfo(XeF4, g) = −(49.28 ± 0.22) kcalth mol−1, and ΔHfo(XeF2, g) = −(25.58 ± 0.21) kcalth mol−1. The average bond dissociation enthalpies,〈Do〉(XeF, 298.15 K), are (29.94 ± 0.16), (31.15 ± 0.13), and (31.62 ± 0.16) kcalth mol−1 in XeF6(g), XeF4(g), and XeF2(g), respectively. The enthalpy of formation of PF3(g) was determined to be −(228.8 ± 0.3) kcalth mol−1.

The enthalpies of formation of plutonium dioxide and plutonium mononitride

Abstract The energies of combustion in oxygen of α-plutonium metal and plutonium mononitride were measured in a bomb calorimeter. The standard enthalpies of formation, ΔH f o (298.15 K), of PuO 2 (c) and PuN(c) were calculated to be −(1055.85±0.72) kJ mol −1 [−(252.35±0.17) kcal mol −1 ] and −(299.2±2.6) kJ mol −1 [−(71.51±0.62) kcal mol −1 ], respectively.

Calorimetric measurements of the low-temperature heat capacity, standard molar enthalpy of formation at 298.15 K, and high-temperature molar enthalpy increments relative to 298.15 K of tungsten disulfide (WS2), and the thermodynamic properties to 1500 K

Low-temperature (5 to 350 K) heat capacity, fluorine combustion, and high-temperature (350 to 1500 K) drop-calorimetric measurements have been performed on a pure synthetic specimen of tungsten disulfide, WS2. The following molar thermodynamic quantities are reported at To = 298.15 K: the standard enthalpy of formation, ΔfHmo(To), −(240.8±3.1) kJ·mol−1; the heat capacity, Cp,mo(To), (63.82±0.32) J·K−1·mol−1; the standard entropy, Smo(To), (67.78±0.34) J·K−1·mol−1; and the standard Gibbs energy of formation, ΔfGmo(To), −(232.1±3.1) kJ·mol−1. The thermodynamic quantities have been calculated to 1500 K. Standard enthalpies of formation deduced from high-temperature equilibrium and e.m.f. studies in the literature are, in general, not in good agreement with one another or the present result. There have been no previous measurements of the low-temperature heat capacity, but the high-temperature enthalpy increments are in fair agreement with results published for WS1.97. There is some indication of a γT (i.e. conduction electrontribution to the heat capacity at low temperatures, but the evidence for this is not strong. The present thermodynamic quantities are consistent with geochemical field observations that molybdenite (MoS2) and not tungstenite (WS2) but tungstates and not molybdates are formed in hydrothermal deposits.

The enthalpies of formation and high-temperature thermodynamic functions of As4S4 and As2S3☆

Abstract The energies of combusion of β-As 4 S 4 and vitreous As 2 S 3 in fluorine were measured in a bomb calorimeter. High-temperature enthalpy increments were also determined by drop calorimetry. The standard enthalpies of formation ΔH f o (298.15 K), were found to be −(134.6±6.7) kJ mol −1 and −(69.6 ± 4.2) kJ mol −1 for β-As 4 S 4 and vitreous As 2 S 3 , respectively. Based on the measured results and data from the literature, the thermodynamic properties of the minerals realgar, α-As 4 S 4 , and orpiment, As 2 S 3 (c) were derived. For realgar at 298.15 K, ΔH f o = −(138.1 ± 6.7) kJ mol −1 , ΔS f o = −(22.3 ± 3.1) J K −1 mol −1 , and ΔG f o = −(131.5 ± 6.8) kJ mol −1 are recommended and, for orpiment at 298.15 K, ΔH f o = −(91.6 ± 4.8) kJ mol −1 , ΔS f o = −(3.1 ± 4.3) J K −1 mol −1 , and ΔG f o = −(90.7 ± 5.0) kJ mol −1 .

Thermodynamic properties of the zeolite stilbite

In this study, calorimetric measurements of the molar enthalpy of formation Δ f H 0 m at 298.15 K, molar heat capacity C 0 p,m (and, thus, the molar entropy 7 S 0 m ) from 5 to 350 K, and enthalpy increments H 0 m ( T ) — H 0 m (298.15 K) from 350 to 500 K were performed on a specimen of stilbite characterized by electron microprobe analysis. The empirical formula of the stilbite was Ca 1.019 Na 0.136 K 0.006 Al 2.180 Si 6.820 O 18 ·7.33 H 2 O. The following thermodynamic properties of stilbite at T = 298.15 K were determined: Δ f H 0 m ( T ) = −11033.6 ± 6.6 kJ mol −1 , C 0 p,m ( T ) = 808.73 ± 1.62 JK −1 mol −1 , S 0 m ( T ) – S 0 m = 805.54 ± 1.61 JK −1 mol −1 , Δ f S 0 m ( T ) = −2990.44 ± 1.86 JK −1 mol −1 and Δ f G 0 m ( T ) = −10142.0 ± 6.6 kJ mol −1 . The present Δ f G 0 m (stilbite) was combined with thermodynamic quantities from the literature to determine an equilibrium temperature for the reaction: stilbite = heulandite + H 2 O that is in close, but not exact, agreement with experimental phase equilibria. Retrieval of Δ f G 0 m (laumontite) from calorimetric and experimental values for the reactions: stilbite = laumontite + 3 SiO 2 + 3 H 2 O and heulandite = laumontite + 3 SiO 2 + 2 H 2 O gave results of −6778.9 and −6765.4 kJ mol −1 .

The enthalpy of formation of uranium hexafluoride

Abstract The energy of combustion of high-purity uranium in fluorine to form uranium hexafluoride was measured in a bomb calorimeter. The standard enthalpies of formation of crystalline and gaseous UF 6 , ΔH f o (UF 6 , c, 298.15 K) = −(2197.7 ± 1.8) kJ mol −1 and ΔH f o (UF 6 , g, 298.15 K) = −(2148.1 ± 1.8) kJ mol −1 , were derived. These values are approximately 11 kJ mol −1 more negative than previous measurements based on fluorine calorimetry.