Claus A. Wulff

The solution thermochemistry of cadmium hydroxide and cadmium oxide The entropy of the aqueous cadmium ion

Abstract The enthalpies of reaction of Cd(OH) 2 and CdO with aqueous HClO 4 are reported as functions of molalities. The results are used to derive the following thermochemical properties for Cd 2+ (aq): S 2 o = − (17.0±0.6) cal K −1 mol −1 , ΔH f o = − 18.1 kcal mol −1 , and ΔG f o = − 18.6 kcal mol −1 .

Thermodynamic properties of mixed valency compounds II. The heat capacities of Rb2SbBr6 and Cs2SbBr6 and phase transitions in Rb2Sb6

Abstract The heat capacities of Rb 2 SbBr 6 and Cs 2 SbBr 6 were measured from 72 and 66 K respectively to room temperature. The heat capacity of the cesium salt was found to be “normal”, while that of the rubidium salt showed a λ- and “hump-like” λ-transition at 220 and 230 K, respectively. This is explained on the basis of existing hypotheses. The entropies of the two salts at 298.16 K are estimated to be: Rb 2 SbBr 6 , (118.3 ± 4) cal th K −1 mol −1 , and Cs 2 SbBr 6 , (109.0 ± 4) cal th K −1 mol −1 .

Thermodynamic properties of mixed valency compounds I. The low temperature heat capacity and phase transitions of ammonium hexabromohypoantimonate

Abstract The heat capacity of ammonium hexabromohypoantimonate, a mixed valency compound, was determined between 70 and 300 K. Two anomalous regions were observed at 212 and 236 K, each with an entropy increment of 1 2 R ln2 . The entropy between 0 and 70 K was estimated to be (33.9±4.0) cal mol−1 K−1. Based on the formula (NH4)2SbBr6 the molar thermodynamic properties: Csat, So, {H o −H o (70 K )} T , and −{G o −H o (70 K )} T , are tabulated from 70 to 300 K. The construction and calibration of a low temperature calorimeter is described.

Thermodynamic properties of mixed valency compounds III. Standard enthalpies of formation, Gibbs free energies of formation, and stabilities of Cs2SbBr6 and Cs2SbBr5

Abstract The standard enthalpies and Gibbs free energies of formation of Cs 2 SbBr 6 and Cs 2 SbBr 5 have been determined from a combination of enthalpies of reaction and solution as: ΔH f o (Cs 2 SbBr 6 , 298.15 K) = −(268.3 ± 0.3) kcal th mol −1 , ΔG f o (Cs 2 SbBr 6 , 298.15 K) = −(253.3 ± 1.5) kcal th mol −1 , ΔH f o (Cs 2 SbBr 5 , 298.15 K) = − (264.5 ± 0.3) kcal th mol −1 , and ΔG f o (Cs 2 SbBr 5 , 298.15 K) = −(251. 4 ± 2) kcal th mol −1 . These values have been shown to accord with decomposition data provided by t.g.a. and d.s.c. techniques. Additional results have been obtained for the solution thermochemistry of CsBr that lead to ΔH f o (CsBr, 298.15 K) = −(94.64 ± 0.05) kcal th mol −1 , ΔH f o (Cs + , aq, 298.15 K) = − (59.35 ± 0.04) kcal th mol −1 , and S o (Cs + , aq, 298.15 K) = (31.5 ± 1) cal th K −1 mol −1 .

Thermal anomalies in stressed teflon

Abstract In the course of testing polytetrafluoroethylene (Teflon) as a calorimetric gasketing material, serendipity revealed a thermal anomaly in stressed film that occurs concomitantly with the well-documented 25°C transition. The magnitude of the excess energy absorption, ca. 35 cal/g, is suggested to be related to the restricted thermal expansion of the film.

Enthalpies of solution of barium benzenedisulfonate A test of limiting-law behavior

Integral enthalpies of solution of barium benzenedisulfonate in water have been measured at 25 °C for molalities between 0.004 and 0.020 mol kg−1. The results are linear in the square root of the molality with a slope close to that predicted by the Debye-Huckel limiting law for 2-2 electrolytes.

The partial molar entropies of aqueous chloro complexes of Cd(II)

Abstract The enthalpies of reaction of CdO + Cd(OH) 2 mixture with aqueous HCl + HClO 4 solutions of variable composition but constant ionic strength, I = 1 mol kg −1 , are presented. The results are interpreted to derive enthalpy increments for the simultaneous reactions leading to the three reported chloro complexes of Cd(II). Several methods of extrapolating the results to the conventional standard state are discussed. The results may be characterized by the following partial molar entropies: CdCl + (aq), 8 .3 ; CdCl 2 (aq), 23; and CdCl 3 − (aq), 48 cal mol −1 K −1 .