Thermochemistry of molybdates IV. Standard enthalpy of formation of lithium molybdate, thermodynamic properties of the aqueous molybdate ion, and thermodynamic stabilities of the alkali-metal molybdates

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Abstract

The enthalpy changes of the processes: Moo3+2LiOH(aq, 0.2 mol dm−3=Li2MoO4(AQ)+H2O(L); δH=−(18.54±0.04)kcalth mol−1 and Li2MoO4(c)=Li2MoO4(aq); δH=−(7.61±0.01)kcalth mol−1, have been determined in a solution calorimeter. These results, when combined with auxiliary thermochemical values, yielded the standard enthalpy of formation, ΔHfo(Li2MoO4, c, 298.15 K) = −(363.26 ± 0.12) kcalth mol−1. Based on thermodynamic and solubility data from the literature for sparingly soluble metal molybdates, ΔGfo(MoO42−, aq, 298.15 K) was deduced to be −(200.0 ± 0.3) kcalth mol−1. This paper also includes estimates of ΔHfo for solid Rb2WO4 and Cs2WO4, and of the enthalpy of sublimation for Cs2WO4. It is also pointed out that ΔHfo(PbMoO4) may be in error, and a value of −245 kcalth mol−1 is suggested.

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    • Thermodynamic characteristics of Li<inf>2</inf>MoO<inf>4</inf>, Li<inf>2</inf>W<inf>0.85</inf>Mo<inf>0.15</inf>O<inf>4</inf> single crystals and stability direction for alkali molybdates

      2020, Journal of Chemical Thermodynamics
      Citation Excerpt :

      It seems that replacing lithium molybdate with more stable caesium molybdate or lithium – caesium molybdate will be more perspective for practice. By measuring the formation enthalpy for Li2MoO4 by two methods and obtaining the value close to value measured by authors [2], we eliminated the contradiction between papers [2] and [11] and established that the formation enthalpy for Li2MoO4 obtained in Argon National Laboratory is more reliable. Lattice enthalpies for alkali molybdates were calculated on the basis of experimental and literature data and their dependences on structural parameters were plotted.

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    This work was performed under the auspices of the U.S. Atomic Energy Commission.

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