Standard enthalpy of solution and formation of cesium chromate. Derived thermodynamic properties of the aqueous chromate,bichromate, and dichromate ions,alkali metal and alkaline earth chromates,and lead chromate

Calorimetric measurements of the enthalpy of solution of cesium chromate gave ΔH_soln = (7622 ± 24) cal_th mol^?1 for a dilution of Cs₂CrO₄·21128H₂O. This result, along with the enthalpy of dilution gave the standard enthalpy of solution, ΔH_soln^o = (7512 ± 31) cal_th mol^?1, whence the standard enthalpy of formation, ΔH_f⁰(Cs₂CrO₄, c, 298.15 K), was calculated to be ?(341.78 ± 0.46) kcal_th mol^?1. Recomputed thermodynamic data for the formation of the other alkali metal chromates have been tabulated. From their solubilities and enthalpies of solution, the standard entropies, S⁰(298 K), of BaCrO₄ and PbCrO₄ were estimated to be (38.9 ± 0.9) and (43.7 ± 1.2) cal_th K^?1 mol^?1, respectively. There is evidence that ΔH_f⁰(SrCrO₄, c, 298.15 K) may be in error. Thermochemical, solubility, and equilibrium data, have been combined to update the thermodynamic properties of the aqueous chromate (CrO₄^2?), bichromate (HCrO₄^?), and dichromate (Cr₂O₇^2?) ions. The new values at 298.15 K are as follows:

	$\text{S}{}^0\text{/}\text{cal}{}_{\mathrm{th}}\text{K}{}^{\mathrm{?1}}\text{mol}{}^{\mathrm{?1}}$	$\text{ΔH}{}_{\mathrm{f}}{}^0\text{/kcal}{}_{\mathrm{th}}\text{mol}{}^{\mathrm{?1}}$	$\text{ΔG}{}_{\mathrm{f}}{}^0\text{/kcal}{}_{\mathrm{th}}\text{mol}{}^{\mathrm{?1}}$
CrO42?(aq)	(13.8 ± 0.5)	?(210.93 ± 0.45)	?(174.8 ± 0.5)
HCrO4?(aq)	(46.6 ± 1.8)	?(210.0 ± 0.7)	?(183.7 ± 0.5)
Cr2O72?(aq)	(67.4 ± 3.9)	?(356.5 ± 1.5)	?(312.8 ± 1.0)
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