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Thermodynamic properties of hydrated cesium pentaborate
J. Chem. Thermodynamics 36 (2004) 317–319 www.elsevier.com/locate/jct
Thermodynamic properties of hydrated cesium pentaborate Zhihong Liu *, Mancheng Hu, Shiyang Gao School of Chemistry and Materials Science, Shaanxi Normal University, Xi’an, Shaanxi 710062, China Received 29 October 2003; accepted 12 December 2003
Abstract The enthalpies of solution of b-CsB5 O8 4H2 O in HCl (aq), and of CsCl in (HCl + H3 BO3 ) (aq) were determined. With the incorporation of the previously determined enthalpy of solution of H3 BO3 in HCl (aq) and the standard molar enthalpies of formation of CsCl (s), H3 BO3 (s), HCl (aq), and H2 O (l), the standard molar enthalpy of formation of b-CsB5 O8 4H2 O of )(4846.29 0.58) kJ mol1 was obtained. Thermodynamic properties of this compound were also calculated by a group contribution method. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: CsB5 O8 4H2 O; Standard molar enthalpy of formation; Thermodynamic properties; Solution calorimetry
1. Introduction
2. Experimental
Alkaline metal cations usually form pentaborates. The polyborate anion of all these borates is [B5 O6 (OH)4 ] . Some of these compounds have useful properties, such as KB5 O8 4H2 O. Its single crystal is a very good non-linear optical material. It is reported that the corresponding Cs-compound have two forms, aCsB5 O8 4H2 O and b-CsB5 O8 4H2 O, and their synthesis and crystal structure have been reported in the literature [1,2]. But there is no report on its thermodynamic properties. Thermodynamic properties play very important roles in scientific research and industrial applications. Li Jun et al. [3,4] reported the standard molar enthalpy of formation of LiB5 O8 5H2 O, NaB5 O8 5H2 O, and KB5 O8 4H2 O. Recently, Zhu Lixia et al. [5] determined the standard molar enthalpy of formation of RbB5 O8 4H2 O. As part of the continuing study of the thermochemistry of hydrated alkaline metal borates, this paper reports the standard molar enthalpy of formation and an estimate of the entropy of formation of b-CsB5 O8 4H2 O.
To a solution of 14.17 g Cs2 CO3 (analytical grade) in 100 cm3 of deionized water was added 10.75 g H3 BO3 (analytical grade). The mixture was heated to the boiling point and maintained with stirring for 1 h. After CO2 was released thoroughly, the clear solution obtained was kept in water bath at T ¼ 303 K. Crystallization began in a few hours. The resulting white powder was filtered, washed with absolute alcohol and then absolute ether, and dried in a vacuum dryer to constant mass at room temperature. The sample was characterized by X-ray powder diffraction (Rigaku D/MAX-IIIC), and all data correspond with those of JCPDS (File No. 22-175) [6], FT-IR spectroscopy (Bruker Equinox 55 spectrometer with KBr pellets at room temperature). The composition of the sample (table 1) was determined by NaOH standard solution in the presence of mannitol for B2 O3 , by gravimetric method of CsB(C6 H5 )4 for Csþ , by TG (Perkin–Elmer TGA7, heating rate of 10 K min1 in flowing N2 ) for H2 O. No impurity lines were observed. The results in table 1 show that the synthetic sample is a pure compound of formula CsB5 O8 4H2 O that is suitable for the following calorimetric experiments. The solution calorimetric procedure involved calorimetric measurements of the enthalpies of solution of
*
Corresponding author. Tel.: +86-29-5307-765; fax: +86-29-5307774. E-mail address: [email protected] (Z. Liu). 0021-9614/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jct.2003.12.007
318
Z. Liu et al. / J. Chem. Thermodynamics 36 (2004) 317–319
TABLE 1 The chemical composition of CsB5 O8 4H2 O as mass fraction
Analytical Theoretical
Csþ
B2 O3
H2 O
0.3427 0.3434
0.4513 0.4497
0.1847 0.1862
CsB5 O8 4H2 O in approximately 1 mol dm3 HCl (aq) according to: CsB5 O8 4H2 O ðsÞ þ HCl ðaqÞ þ 3H2 O ðlÞ ¼ Csþ ðaqÞ þ Cl ðaqÞ þ 5H3 BO3 ðaqÞ In addition, the enthalpies of solution of H3 BO3 in HCl (aq), and of CsCl (mass fraction P 0.9999) in (HCl + H3 BO3 ) (aq) that consisted of approximately 1 mol dm3 HCl (aq) and the calculated amount of H3 BO3 were determined. The standard molar enthalpy of formation of CsB5 O8 4H2 O could be obtained by solution calorimetry in combination with the standard molar enthalpies of formation of CsCl (s), H3 BO3 (s), HCl (aq), and H2 O (l). The HCl solvent was prepared from analytical grade hydrochloric acid and deionized water, and its concentration, 0.9764 mol dm3 , was determined by titration with standard sodium carbonate, and its density, 1.0168 g cm3 , was taken from literature [7]. A RD496-III heat conduction microcalorimeter (Southwest Institute of Electron Engineering, China) was used and has been described in detail previously [8]. The temperature of the calorimetric experiment was T ¼ 298:15 K. Additional double-layer glass tubes were put in the 15 cm3 stainless steel sample cell and reference cell of the calorimeter. This was done to prevent corrosion of the stainless steel sample and reference cell by HCl (aq). The lining in the double-layer glass tube containing HCl (aq) was broken by a rod after thermal equilibration for at least 2 h. The HCl (aq) was mixed with solid sample in the outer glass tube, then the thermal response was recorded automatically on an computer. Total time required for the complete reaction was about 0.5 h. There were no solid residues observed after the reactions in each calorimetric experiment. To check the performance of the RD496-III heat conduction microcalorimeter, calorimetric measurements on the enthalpy of solution of KCl (mass fraction P 0.9999) in deionized water and of THAM (trishydroxymethylaminomethane, mass fraction P 0.9999) in 0.1 mol dm3 HCl (aq) were made, respectively. The average experimental values (17.23 0.04) kJ mol1 of Dsol Hm of KCl (s) and )(29.75 0.04) kJ mol1 of THAM are in excellent agreement with those of 17.234 kJ mol1 reported in the literature [9] and )(29.73 0.04) kJ mol1 reported in the literature [10], respectively. This shows that the device for measuring the enthalpy of solution used in this work is reliable.
3. Results and discussion The molar enthalpies of solution of CsCl in (HCl + H3 BO3 ) (aq) and of CsB5 O8 4H2 O in HCl (aq) at T ¼ 298:15 K are listed in tables 2 and 3, in which m is the mass of sample, Dsol Hm is the molar enthalpy of solution of solute, and the uncertainty is estimated as twice the standard deviation of the mean. Table 4 gives the thermochemical cycle for the derivation of the standard molar enthalpy of formation of CsB5 O8 4H2 O. The molar enthalpy of solution of H3 BO3 (s) of (21.83 0.08) kJ mol1 in approximately 1 mol dm3 HCl (aq) was taken from previous work [10]. The standard molar enthalpies of formation of H3 BO3 (s), H2 O (l) and CsCl (s) were taken directly from the NBS tables [11], namely )(1094.33 0.06) kJ mol1 , )(285.83 0.06) kJ mol1 and )(443.04 0.08) kJ mol1 , respectively. The standard molar enthalpy of formation of HCl (aq) and the enthalpy of dilution of HCl (aq) were calculated from the NBS tables [11], respectively. From these data, the standard molar enthalpy of formation of CsB5 O8 4H2 O was calculated to be )(4846.29 0.58) kJ mol1 . The enthalpy of formation of CsB5 O8 4H2 O can also be estimated by a group contribution method [12], which can be expressed as shown in following equation:
TABLE 2 The molar enthalpies of solution of CsCl in (HCl + H3 BO3 ) (aq) at T ¼ 298:15 Ka No.
m/mg
Dsol Hm /(kJ mol1 )
1 2 3 4 5
3.10 3.02 3.06 2.96 3.04
16.26 16.32 16.00 16.28 16.43 16:26 0:14b
Mean a
3
In each experiment, 2.00 cm of HCl (aq) were used. Uncertainty is estimated as twice the standard deviation of the mean. b
TABLE 3 The molar enthalpies of solution of CsB5 O8 4H2 O in 0.9764 mol dm3 HCl (aq) at T ¼ 298:15 Ka No.
m/mg
Dsol Hm /(kJ mol1 )
1 2 3 4 5
6.32 6.18 6.06 6.30 6.42
78.97 79.04 78.80 78.79 78.91
Mean a
78:90 0:10b
In each experiment, 2.00 cm3 of HCl (aq) were used. Uncertainty is estimated as twice the standard deviation of the mean. b
Z. Liu et al. / J. Chem. Thermodynamics 36 (2004) 317–319
319
TABLE 4 Thermochemical cycle and results for the derivation of Df Hm (CsB5 O8 4H2 O, 298.15 K) Dr Hm /(kJ mol1 )
Reaction 1. 2. 3. 4. 5. 6. 7. 8. 9.
CsB5 O8 4H2 O (s) + 120.03(HCl 55.826H2 O) ¼ Csþ (aq) + Cl (aq) + 5H3 BO3 (aq) + 119.03(HCl 56.270H2 O) 5H3 BO3 (aq) + 119.03(HCl 56.270H2 O) ¼ 5H3 BO3 (s) + 119.03(HCl 56.270H2 O) Csþ (aq) + Cl (aq) + 5H3 BO3 (aq) + 119.03(HCl 56.270H2 O) ¼ CsCl (s) + 5H3 BO3 (aq) + 119.03(HCl 56.270H2 O) 120.03(HCl 56.270H2 O) ¼ 120.03(HCl 55.826H2 O) + 53.270H2 O (l) 1/2H2 (g) + 1/2Cl2 (g) + 56.270H2 O (l) ¼ HCl 56.270H2 O CsCl (s) ¼ Cs (s) + 1/2Cl2 (g) 5H3 BO3 (s) ¼ 5B (s) + 15/2H2 (g) + 15/2O2 (g) 3H2 (g) + 3/2O2 (g) ¼ 3H2 O (l) CsB5 O8 4H2 O (s) ¼ Cs (s) + 5B (s) + 4H2 (g) + 6O2 (g)
Df Hm ðCsB5 O6 ðOHÞ4 2H2 O; sÞ ¼ Df Hm ðCsþ ; aqÞ 2Df Hm ðH2 OÞ
þ
Df Hm ð½B5 O6 ðOHÞ4 ; aqÞþ
in which the Df Hm of )3989.97 kJ mol1 of [B5 O6 (OH)4 ] and )290.42 kJ mol1 of structural H2 O were taken from the literature [12], the Df Hm of )258.28 kJ mol1 of Csþ was taken from the NBS tables [11]. The standard molar enthalpy of formation is, using this scheme, )4829.09 kJ mol1 . The relative error is 0.355%. We also used a group contribution method to calculate Df Hm of CsB5 O6 (OH)4 2H2 O to be )4388.31 kJ mol1 according to the following equation: Df Gm ðCsB5 O6 ðOHÞ4 2H2 O; sÞ ¼
Df Gm ðCsþ ; aqÞ þ Df Gm ð½B5 O6 ðOHÞ4 ; aqÞþ 2Df Gm ðH2 OÞ in which the Df Gm of )3621.73 kJ mol1 of [B5 O6 (OH)4 ] and )237.28 kJ mol1 of structural H2 O were taken from the literature [12], and the Df Gm of )292.02 kJ mol1 of Csþ was taken from the NBS tables [11]. Combining the Df Hm of CsB5 O8 4H2 O, the standard molar entropy of formation of CsB5 O8 4H2 O has been calculated at )1536.07 J mol1 K1 according to following equation: Df Sm ¼ ðDf Hm Df Gm Þ=T :
78.90 0.10 )109.15 0.40 )16.26 0.14 1.05 0.04 )165.45 0.10 443.04 0.08 5471.65 0.3 )857.49 0.18 4846.29 0.58
Finally, the standard molar entropy of CsB5 O8 4H2 O was calculated to be 332.02 J mol1 K1 according to reaction (9) in table 4. The standard molar entropies of the elements were taken from the NBS tables [11] to be (85.23, 5.86, 130.684, and 205.138) J mol1 K1 for Cs (s), B (s), H2 (g), and O2 (g), respectively. References [1] H. Behm, Acta Crystallogr. C40 (1984) 1114–1116. [2] N. Penin, L. Seguin, B. Gerand, M. Touboul, G. Nowogrocki, J. Alloys Compd. 334 (2002) 97–109. [3] J. Li, B. Li, S.Y. Gao, J. Chem. Thermodyn. 30 (1998) 681–688. [4] J. Li, B. Li, S.Y. Gao, J. Chem. Thermodyn. 30 (1998) 425–432. [5] L.X. Zhu, T. Yue, S.Y. Gao, S.P. Xia, J. Chem. Thermodyn. 35 (2003) 433–438. [6] W.F. Mcclune, M.E. Mrose, B. Post, S. Weissmann, H.F. Mcmurdie, Powder Diffraction File, JCPDS International Centre for Diffraction Data, 1979. [7] K. Tao, Soviet Chemical Handbook [III], Science Press, Beijing, 1963. [8] M. Ji, M.Y. Liu, Sh.L. Gao, Q.Zh. Shi, Instr. Sci. Technol. 29 (1) (2001) 53–57. [9] R.C. Weast, CRC Handbook of Chemistry and Physics, 70th ed., CRC Press, Boca Raton, FL, 1989. [10] J. Li, S.Y. Gao, Sh.P. Xia, B. Li, R.Z. Hu, J. Chem. Thermodyn. 29 (1997) 491–497. [11] D.D. Wagman, W.H. Evans, V.B. Parker, R.H. Schumm, I. Halow, S.M. Bailey, K.L. Chumey, R.L Nuttall, The NBS Tables of Chemical Thermodynamic Properties, 1982. [12] J. Li, B. Li, S.Y. Gao, Phys. Chem. Miner. 27 (2000) 342–346.
Thermodynamic properties of hydrated cesium pentaborate Zhihong Liu *, Mancheng Hu, Shiyang Gao School of Chemistry and Materials Science, Shaanxi Normal University, Xi’an, Shaanxi 710062, China Received 29 October 2003; accepted 12 December 2003
Abstract The enthalpies of solution of b-CsB5 O8 4H2 O in HCl (aq), and of CsCl in (HCl + H3 BO3 ) (aq) were determined. With the incorporation of the previously determined enthalpy of solution of H3 BO3 in HCl (aq) and the standard molar enthalpies of formation of CsCl (s), H3 BO3 (s), HCl (aq), and H2 O (l), the standard molar enthalpy of formation of b-CsB5 O8 4H2 O of )(4846.29 0.58) kJ mol1 was obtained. Thermodynamic properties of this compound were also calculated by a group contribution method. Ó 2004 Elsevier Ltd. All rights reserved. Keywords: CsB5 O8 4H2 O; Standard molar enthalpy of formation; Thermodynamic properties; Solution calorimetry
1. Introduction
2. Experimental
Alkaline metal cations usually form pentaborates. The polyborate anion of all these borates is [B5 O6 (OH)4 ] . Some of these compounds have useful properties, such as KB5 O8 4H2 O. Its single crystal is a very good non-linear optical material. It is reported that the corresponding Cs-compound have two forms, aCsB5 O8 4H2 O and b-CsB5 O8 4H2 O, and their synthesis and crystal structure have been reported in the literature [1,2]. But there is no report on its thermodynamic properties. Thermodynamic properties play very important roles in scientific research and industrial applications. Li Jun et al. [3,4] reported the standard molar enthalpy of formation of LiB5 O8 5H2 O, NaB5 O8 5H2 O, and KB5 O8 4H2 O. Recently, Zhu Lixia et al. [5] determined the standard molar enthalpy of formation of RbB5 O8 4H2 O. As part of the continuing study of the thermochemistry of hydrated alkaline metal borates, this paper reports the standard molar enthalpy of formation and an estimate of the entropy of formation of b-CsB5 O8 4H2 O.
To a solution of 14.17 g Cs2 CO3 (analytical grade) in 100 cm3 of deionized water was added 10.75 g H3 BO3 (analytical grade). The mixture was heated to the boiling point and maintained with stirring for 1 h. After CO2 was released thoroughly, the clear solution obtained was kept in water bath at T ¼ 303 K. Crystallization began in a few hours. The resulting white powder was filtered, washed with absolute alcohol and then absolute ether, and dried in a vacuum dryer to constant mass at room temperature. The sample was characterized by X-ray powder diffraction (Rigaku D/MAX-IIIC), and all data correspond with those of JCPDS (File No. 22-175) [6], FT-IR spectroscopy (Bruker Equinox 55 spectrometer with KBr pellets at room temperature). The composition of the sample (table 1) was determined by NaOH standard solution in the presence of mannitol for B2 O3 , by gravimetric method of CsB(C6 H5 )4 for Csþ , by TG (Perkin–Elmer TGA7, heating rate of 10 K min1 in flowing N2 ) for H2 O. No impurity lines were observed. The results in table 1 show that the synthetic sample is a pure compound of formula CsB5 O8 4H2 O that is suitable for the following calorimetric experiments. The solution calorimetric procedure involved calorimetric measurements of the enthalpies of solution of
*
Corresponding author. Tel.: +86-29-5307-765; fax: +86-29-5307774. E-mail address: [email protected] (Z. Liu). 0021-9614/$ - see front matter Ó 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.jct.2003.12.007
318
Z. Liu et al. / J. Chem. Thermodynamics 36 (2004) 317–319
TABLE 1 The chemical composition of CsB5 O8 4H2 O as mass fraction
Analytical Theoretical
Csþ
B2 O3
H2 O
0.3427 0.3434
0.4513 0.4497
0.1847 0.1862
CsB5 O8 4H2 O in approximately 1 mol dm3 HCl (aq) according to: CsB5 O8 4H2 O ðsÞ þ HCl ðaqÞ þ 3H2 O ðlÞ ¼ Csþ ðaqÞ þ Cl ðaqÞ þ 5H3 BO3 ðaqÞ In addition, the enthalpies of solution of H3 BO3 in HCl (aq), and of CsCl (mass fraction P 0.9999) in (HCl + H3 BO3 ) (aq) that consisted of approximately 1 mol dm3 HCl (aq) and the calculated amount of H3 BO3 were determined. The standard molar enthalpy of formation of CsB5 O8 4H2 O could be obtained by solution calorimetry in combination with the standard molar enthalpies of formation of CsCl (s), H3 BO3 (s), HCl (aq), and H2 O (l). The HCl solvent was prepared from analytical grade hydrochloric acid and deionized water, and its concentration, 0.9764 mol dm3 , was determined by titration with standard sodium carbonate, and its density, 1.0168 g cm3 , was taken from literature [7]. A RD496-III heat conduction microcalorimeter (Southwest Institute of Electron Engineering, China) was used and has been described in detail previously [8]. The temperature of the calorimetric experiment was T ¼ 298:15 K. Additional double-layer glass tubes were put in the 15 cm3 stainless steel sample cell and reference cell of the calorimeter. This was done to prevent corrosion of the stainless steel sample and reference cell by HCl (aq). The lining in the double-layer glass tube containing HCl (aq) was broken by a rod after thermal equilibration for at least 2 h. The HCl (aq) was mixed with solid sample in the outer glass tube, then the thermal response was recorded automatically on an computer. Total time required for the complete reaction was about 0.5 h. There were no solid residues observed after the reactions in each calorimetric experiment. To check the performance of the RD496-III heat conduction microcalorimeter, calorimetric measurements on the enthalpy of solution of KCl (mass fraction P 0.9999) in deionized water and of THAM (trishydroxymethylaminomethane, mass fraction P 0.9999) in 0.1 mol dm3 HCl (aq) were made, respectively. The average experimental values (17.23 0.04) kJ mol1 of Dsol Hm of KCl (s) and )(29.75 0.04) kJ mol1 of THAM are in excellent agreement with those of 17.234 kJ mol1 reported in the literature [9] and )(29.73 0.04) kJ mol1 reported in the literature [10], respectively. This shows that the device for measuring the enthalpy of solution used in this work is reliable.
3. Results and discussion The molar enthalpies of solution of CsCl in (HCl + H3 BO3 ) (aq) and of CsB5 O8 4H2 O in HCl (aq) at T ¼ 298:15 K are listed in tables 2 and 3, in which m is the mass of sample, Dsol Hm is the molar enthalpy of solution of solute, and the uncertainty is estimated as twice the standard deviation of the mean. Table 4 gives the thermochemical cycle for the derivation of the standard molar enthalpy of formation of CsB5 O8 4H2 O. The molar enthalpy of solution of H3 BO3 (s) of (21.83 0.08) kJ mol1 in approximately 1 mol dm3 HCl (aq) was taken from previous work [10]. The standard molar enthalpies of formation of H3 BO3 (s), H2 O (l) and CsCl (s) were taken directly from the NBS tables [11], namely )(1094.33 0.06) kJ mol1 , )(285.83 0.06) kJ mol1 and )(443.04 0.08) kJ mol1 , respectively. The standard molar enthalpy of formation of HCl (aq) and the enthalpy of dilution of HCl (aq) were calculated from the NBS tables [11], respectively. From these data, the standard molar enthalpy of formation of CsB5 O8 4H2 O was calculated to be )(4846.29 0.58) kJ mol1 . The enthalpy of formation of CsB5 O8 4H2 O can also be estimated by a group contribution method [12], which can be expressed as shown in following equation:
TABLE 2 The molar enthalpies of solution of CsCl in (HCl + H3 BO3 ) (aq) at T ¼ 298:15 Ka No.
m/mg
Dsol Hm /(kJ mol1 )
1 2 3 4 5
3.10 3.02 3.06 2.96 3.04
16.26 16.32 16.00 16.28 16.43 16:26 0:14b
Mean a
3
In each experiment, 2.00 cm of HCl (aq) were used. Uncertainty is estimated as twice the standard deviation of the mean. b
TABLE 3 The molar enthalpies of solution of CsB5 O8 4H2 O in 0.9764 mol dm3 HCl (aq) at T ¼ 298:15 Ka No.
m/mg
Dsol Hm /(kJ mol1 )
1 2 3 4 5
6.32 6.18 6.06 6.30 6.42
78.97 79.04 78.80 78.79 78.91
Mean a
78:90 0:10b
In each experiment, 2.00 cm3 of HCl (aq) were used. Uncertainty is estimated as twice the standard deviation of the mean. b
Z. Liu et al. / J. Chem. Thermodynamics 36 (2004) 317–319
319
TABLE 4 Thermochemical cycle and results for the derivation of Df Hm (CsB5 O8 4H2 O, 298.15 K) Dr Hm /(kJ mol1 )
Reaction 1. 2. 3. 4. 5. 6. 7. 8. 9.
CsB5 O8 4H2 O (s) + 120.03(HCl 55.826H2 O) ¼ Csþ (aq) + Cl (aq) + 5H3 BO3 (aq) + 119.03(HCl 56.270H2 O) 5H3 BO3 (aq) + 119.03(HCl 56.270H2 O) ¼ 5H3 BO3 (s) + 119.03(HCl 56.270H2 O) Csþ (aq) + Cl (aq) + 5H3 BO3 (aq) + 119.03(HCl 56.270H2 O) ¼ CsCl (s) + 5H3 BO3 (aq) + 119.03(HCl 56.270H2 O) 120.03(HCl 56.270H2 O) ¼ 120.03(HCl 55.826H2 O) + 53.270H2 O (l) 1/2H2 (g) + 1/2Cl2 (g) + 56.270H2 O (l) ¼ HCl 56.270H2 O CsCl (s) ¼ Cs (s) + 1/2Cl2 (g) 5H3 BO3 (s) ¼ 5B (s) + 15/2H2 (g) + 15/2O2 (g) 3H2 (g) + 3/2O2 (g) ¼ 3H2 O (l) CsB5 O8 4H2 O (s) ¼ Cs (s) + 5B (s) + 4H2 (g) + 6O2 (g)
Df Hm ðCsB5 O6 ðOHÞ4 2H2 O; sÞ ¼ Df Hm ðCsþ ; aqÞ 2Df Hm ðH2 OÞ
þ
Df Hm ð½B5 O6 ðOHÞ4 ; aqÞþ
in which the Df Hm of )3989.97 kJ mol1 of [B5 O6 (OH)4 ] and )290.42 kJ mol1 of structural H2 O were taken from the literature [12], the Df Hm of )258.28 kJ mol1 of Csþ was taken from the NBS tables [11]. The standard molar enthalpy of formation is, using this scheme, )4829.09 kJ mol1 . The relative error is 0.355%. We also used a group contribution method to calculate Df Hm of CsB5 O6 (OH)4 2H2 O to be )4388.31 kJ mol1 according to the following equation: Df Gm ðCsB5 O6 ðOHÞ4 2H2 O; sÞ ¼
Df Gm ðCsþ ; aqÞ þ Df Gm ð½B5 O6 ðOHÞ4 ; aqÞþ 2Df Gm ðH2 OÞ in which the Df Gm of )3621.73 kJ mol1 of [B5 O6 (OH)4 ] and )237.28 kJ mol1 of structural H2 O were taken from the literature [12], and the Df Gm of )292.02 kJ mol1 of Csþ was taken from the NBS tables [11]. Combining the Df Hm of CsB5 O8 4H2 O, the standard molar entropy of formation of CsB5 O8 4H2 O has been calculated at )1536.07 J mol1 K1 according to following equation: Df Sm ¼ ðDf Hm Df Gm Þ=T :
78.90 0.10 )109.15 0.40 )16.26 0.14 1.05 0.04 )165.45 0.10 443.04 0.08 5471.65 0.3 )857.49 0.18 4846.29 0.58
Finally, the standard molar entropy of CsB5 O8 4H2 O was calculated to be 332.02 J mol1 K1 according to reaction (9) in table 4. The standard molar entropies of the elements were taken from the NBS tables [11] to be (85.23, 5.86, 130.684, and 205.138) J mol1 K1 for Cs (s), B (s), H2 (g), and O2 (g), respectively. References [1] H. Behm, Acta Crystallogr. C40 (1984) 1114–1116. [2] N. Penin, L. Seguin, B. Gerand, M. Touboul, G. Nowogrocki, J. Alloys Compd. 334 (2002) 97–109. [3] J. Li, B. Li, S.Y. Gao, J. Chem. Thermodyn. 30 (1998) 681–688. [4] J. Li, B. Li, S.Y. Gao, J. Chem. Thermodyn. 30 (1998) 425–432. [5] L.X. Zhu, T. Yue, S.Y. Gao, S.P. Xia, J. Chem. Thermodyn. 35 (2003) 433–438. [6] W.F. Mcclune, M.E. Mrose, B. Post, S. Weissmann, H.F. Mcmurdie, Powder Diffraction File, JCPDS International Centre for Diffraction Data, 1979. [7] K. Tao, Soviet Chemical Handbook [III], Science Press, Beijing, 1963. [8] M. Ji, M.Y. Liu, Sh.L. Gao, Q.Zh. Shi, Instr. Sci. Technol. 29 (1) (2001) 53–57. [9] R.C. Weast, CRC Handbook of Chemistry and Physics, 70th ed., CRC Press, Boca Raton, FL, 1989. [10] J. Li, S.Y. Gao, Sh.P. Xia, B. Li, R.Z. Hu, J. Chem. Thermodyn. 29 (1997) 491–497. [11] D.D. Wagman, W.H. Evans, V.B. Parker, R.H. Schumm, I. Halow, S.M. Bailey, K.L. Chumey, R.L Nuttall, The NBS Tables of Chemical Thermodynamic Properties, 1982. [12] J. Li, B. Li, S.Y. Gao, Phys. Chem. Miner. 27 (2000) 342–346.