Standard Molar Enthalpies of Formation for the Two Hydrated Calcium Borates xCaO·5B₂O₃·yH₂O (x = 2 and 4, y = 5 and 7)

Abstract

Two pure calcium borates of 2CaO·5B2O3·5H2O (I) and β-4CaO·5B2O3·7H2O (II) have been synthesized under hydrothermal condition and characterized by X-ray diffraction, infrared spectra, and thermogravimetric analysis as well as by chemical analysis. All the enthalpies of solution were measured at 298.15 K by using a heat conduction microcalorimeter. The molar enthalpies of solution of (I) and (II) in 2.00 cm3 of 1 mol·dm-3 HCl(aq) were measured to be −(60.30 ± 0.78) kJ·mol-1 and −(158.63 ± 0.72) kJ·mol-1, respectively. The molar enthalpies of solution of H3BO3(s) in 2.00 cm3 of 1 mol·dm-3 HCl(aq) and of CaO(s) in 2.00 cm3 of (HCl + H3BO3) aqueous solution were measured to be (21.84 ± 0.05) kJ·mol-1 and −(188.59 ± 0.42) kJ·mol-1, respectively. The enthalpies change of borates (I) and (II) formation from the reaction of reagents in the solid phase, −(98.3 ± 1.3) kJ·mol-1 and −(377.2 ± 1.9) kJ·mol-1 were calculated respectively on the basis of the appropriate thermochemical cycles. From these data and the standard molar enthalpies of formation of CaO(s), H3BO3(s), and H2O(l), the standard molar enthalpies of formation were calculated as −(9457.9 ± 8.3) kJ·mol-1 for (I) and −(11578.7 ± 8.9) kJ·mol-1 for (II), respectively.

Hydrothermal synthesis and thermochemistry of metalloborophosphate of Na2[CuB3P2O11(OH)]·0.67H2O

“…Table 4 gives the thermochemical cycle used for the derivation of the standard molar enthalpy of formation of Na 2 [CuB 3 P 2 O 11 (OH)]Á0.67H 2 O. The mean molar enthalpy of solution of H 3 BO 3 (s) of (21.84 ± 0.05) in 2.00 cm 3 of 1 mol Á dm À3 HCl (aq) was taken from our previous work [8]. The enthalpy of dilution of HCl (aq) was calculated from NBS tables [16].…”

“…Applying Hess's law, D r H m ð6Þ can be calculated according to the following expression: All the enthalpies of solution were measured with an RD496-III heat conduction microcalorimeter (Southwest Institute of Electron Engineering, China), which has been described in detail previously [8,13]. The total time required for the complete dissolution reaction was about 0.5 h. There were no solid residues observed after the reactions in each calorimetric experiment.…”

“…As for the thermochemistry of borates, we have measured the standard molar enthalpies of formation of many metal borates [4][5][6][7][8][9][10][11]. However, studies of the thermochemistry of the borophosphates are not reported in the literature.…”

Thermodynamic properties of microporous materials for two copper borates, MCuB7O12·H2O (M=Na,K)

“…Applying Hess's law, D r H o m (6) can be calculated according to the following expression: All the enthalpies of solution were measured with a RD496-2000 heat conduction microcalorimeter (Mianyang CP Thermal Analysis Instrument Co., LTD, China), which has been described in detail previously [11,12]. Calorimetric experiments were performed five times at T = 298.15 K. The total time required for the complete dissolution reaction was about 0.5 h. There were no solid residues observed after the reactions in each calorimetric experiment.…”

“…Tables 6 and 7 give the thermochemical cycles for the derivation of the standard molar enthalpies of formation of NaCuB 7 O 12 Á H 2 O (s) and KCuB 7 O 12 Á H 2 O (s), respectively. The mean molar enthalpy of solution of 5.3 mg of H 3 BO 3 (s) of (21.84 ± 0.05) kJ Á mol À1 in 2.00 cm 3 of 1 mol Á dm À3 HCl (aq) was taken from the literature [12]. The standard molar enthalpy of formation of HCl (aq) and the enthalpy of dilution of HCl (aq) were calculated from NBS tables [16].…”