Table 2.

Sample composition, drop solution enthalpies, and formation enthalpies of the CaMnO samples.

Compositiona,b	Measured ΔHds of the oxide⋅nH2O, kJ/molc	ΔHds,cor of the oxide, kJ/mold	ΔHf-ox, kJ/mol	ΔHf-ox*,kJ/mol	ΔH°f, kJ/mol
Ca0.39⋅Mn(3+)0.21⋅Mn(4+)0.79⋅O2.29⋅0.60H2Oe	174.05 ± 1.46 (12)	132.49 ± 1.46	−53.57 ± 3.03	−86.61 ± 2.85	−934.56 ± 2.22
Ca0.39⋅Mn(3+)0.13⋅Mn(4+)0.87⋅O2.33⋅0.48H2Oe	168.20 ± 1.45 (12)	135.05 ± 1.45	−52.29 ± 3.02	−88.74 ± 2.84	−902.95 ± 2.22
Ca0.39⋅Mn(3+)0.09⋅Mn(4+)0.91⋅O2.35⋅0.43H2Oe	165.65 ± 1.67 (10)	135.82 ± 1.67	−50.89 ± 3.24	−89.26 ± 3.08	−891.05 ± 2.22
Ca0.39⋅Mn(3+)0.06⋅Mn(4+)0.94⋅O2.37⋅0.30H2Oe	158.00 ± 1.26 (10)	137.28 ± 1.27	−50.99 ± 2.85	−90.56 ± 2.66	−854.52 ± 2.22
Ca0.39⋅Mn(3+)0.05⋅Mn(4+)0.95⋅O2.37⋅0.28H2Oe	158.25 ± 1.20 (8)	138.62 ± 1.20	−52.13 ± 2.79	−91.87 ± 2.59	−850.18 ± 2.22
Ca0.43⋅Mn(3+)0.37⋅Mn(4+)0.63⋅O2.24⋅0.43H2Of	154.12 ± 2.03 (8)	124.42 ± 2.03	−55.89 ± 3.62	−82.32 ± 3.48	−899.49 ± 2.22
Ca0.43⋅Mn(3+)0.39⋅Mn(4+)0.61⋅O2.23⋅0.42H2Of	154.87 ± 1.42 (10)	125.61 ± 1.42	−58.18 ± 2.99	−83.64 ± 2.81	−896.70 ± 2.22
Ca0.43⋅Mn(3+)0.28⋅Mn(4+)0.72⋅O2.29⋅0.35H2Of	150.69 ± 1.41 (8)	126.48 ± 1.41	−53.60 ± 2.98	−83.88 ± 2.80	−880.44 ± 2.22
Ca0.43⋅Mn(3+)0.29⋅Mn(4+)0.71⋅O2.28⋅0.22H2Of	142.12 ± 0.94 (8)	126.77 ± 0.95	−54.41 ± 2.59	−84.23 ± 2.37	−843.34 ± 2.22
Ca0.43⋅Mn(3+)0.28⋅Mn(4+)0.72⋅O2.29⋅0.15H2Of	137.99 ± 1.73 (8)	127.67 ± 1.73	−54.63 ± 3.30	−85.05 ± 3.14	−823.06 ± 2.22

^aSample compositions are normalized to 1 mol of manganese.

^bQuality control was run between different samples of CaMnO using a reference standard of manganese dioxide (Sigma–Aldrich) for the Murray titration method for manganese AOS and speciation.

^cError is 2 SDs of the mean. Value in parentheses is number of experiments performed. Uncertainties are propagated in subsequent calculations.

^dΔH_ds,cor formula compositions are normalized to 1 mol of manganese. The enthalpy of formation (ΔH_f-ox) from the oxides for the reaction mCaO + 0.5(1-y)Mn₂O₃ + yMnO₂ + nH₂O = Ca_mMnO_(1.5+m+0.5y)⋅nH₂O and the enthalpy of formation (ΔH_f-ox*) from the oxides for the reaction mCaO + 0.5Mn₂O₃ + 0.25yO₂ + nH₂O = Ca_mMnO_(1.5+m+0.5y)·nH₂O were computed using appropriate thermochemical cycles that included the use of measured drop solution enthalpies (ΔH_ds) of the CaMnO samples and of ΔH_dsCaO = (−90.70±1.69) kJ/mol (32), ΔH_dsMn₂O₃ = 154.87±1.00 kJ/mol (30), and ΔH_dsMnO₂ = 124.92±1.03 kJ/mol (30). Heats of formation (ΔH^o_f) were computed using standard formation enthalpies (33) of binary oxides from the elements and heat content (33) of O₂.

^eCaMnO sample contains 43.06 ± 0.01 wt% manganese (0.78₄ mol) and 12.40 ± 0.01 wt% calcium (0.30₉ mol).

^fCaMnO sample contains 49.00 ± 0.01 wt% manganese (0.89₂ mol) and 15.28 ± 0.01 wt% calcium (0.38₁ mol).