Calorimetric Determination of the Formation Enthalpies of Cs Polymolybdates at 298.15 K and 0.1 MPa

Abstract

Samples of cesium polymolybdates Cs2Mo n O3n+1 with n = 2, 3, 5, and 7 have been synthesized by melting and cooling stoichiometric mixtures of commercially available Cs2MoO4 and MoO3 powders. The single-phase character of the samples has been checked by X-ray diffraction. The standard enthalpies of formation of the Cs2Mo n O3n+1 polymolybdates with n = 1, 2, 3, 5, and 7 have been measured by solution calorimetry in dilute (CsOH·H2O) solvent at 298.15 K under 0.1 MPa. The values found for the mono and dimolybdates, Δf H° (Cs2MoO4) = −1513.56 ± 1.11 kJ mol–1, Δf H° (Cs2Mo2O7) = −2301.84 ± 2.37 kJ mol–1, are in good agreement with the already available calorimetric measurements. To our knowledge, this is the first time that the enthalpies of formation of cesium tri, penta, and heptamolybdates are measured: Δf H° (Cs2Mo3O10) = −3077.17 ± 3.47 kJ mol–1, Δf H° (Cs2Mo5O16) = −4601.70 ± 5.96 kJ mol–1, and Δf H° (Cs2Mo7O22) = −6087.16 ± 8.79 kJ mol–1, respectively. The convex shape of the curve constructed from the formation enthalpies of the Cs2Mo n O3n+1 polymolybdates referred to the Cs2MoO4 and MoO3 oxides is consistent with the Cs2MoO4–MoO3 pseudobinary diagram.

Report of the Double-Molybdate Phase Cs2Ba(MoO4)2 with a Palmierite Structure and Its Thermodynamic Characterization

“… b Expanded uncertainty U with a coverage factor k = 2, corresponding to a 95% confidence interval. c The selected value is the average of the data reported in refs ( 36 − 38 and 55 ). …”

“…When the aforementioned enthalpy of reaction is combined with the enthalpies of formation of Cs 2 MoO 4 (cr) and BaMoO 4 (cr), the standard enthalpy of formation of Cs 2 Ba(MoO 4 ) 2 (cr) is finally derived as Δ f H m °(Cs 2 Ba(MoO 4 ) 2 , cr, 298.15 K) = −3066.6 ± 3.1 kJ mol –1 . The selected value for the enthalpy of formation of Cs 2 MoO 4 (cr) is the average of the data reported by O’Hare and Hoekstra 37 and revised by Cordfunke and Konings 38 (−1514.5 ± 1.0 kJ mol –1 ), the data reported by Smith et al 36 (−1514.69 ± 1.54 kJ mol –1 ) and by Benigni et al 55 (−1513.56 ± 1.11 kJ mol –1 ). The enthalpy of formation of BaMoO 4 was taken from the critical review of Gamsjäger and Morishita, 56 on the basis of the data measured by O’Hare 57 and Shukla et al 58 …”

“… a Measurements were performed in the temperature interval T = 298.15 ± 0.30 K. The enthalpy of formation of Cs 2 Ba­(MoO 4 ) 2 was calculated using the relation Δ f H m °(6) = Δ sln H­(2) + Δ sln H (3) – Δ sln H (1) + Δ f H m °(4) + Δ f H m °(5). b Expanded uncertainty U with a coverage factor k = 2, corresponding to a 95% confidence interval. c The selected value is the average of the data reported in refs − and . …”

Vaporization and thermodynamics of the Cs2O–MoO3 system studied using high‐temperature mass spectrometry

“…1 The thermodynamic properties of cesium dimolybdate and polymolybdates are also available in the scientific literature. [16][17][18] Vaporization of cesium molybdate has been repeatedly investigated. [19][20][21][22][23] The standard enthalpies of formation of alkali metal molybdates, including cesium molybdate, obtained by the Knudsen effusion mass spectrometric method were summarized in a review.…”

“…The standard enthalpy of formation of crystalline Cs 2 MoO 4 at 298 K was −1514.6 ± 0.5 kJ/mol 1 . The thermodynamic properties of cesium dimolybdate and polymolybdates are also available in the scientific literature 16–18 …”