- Email: [email protected]
The standard molar enthalpies of formation of SrTeO3and SrTe2O5
J. Chem. Thermodynamics 1998, 30, 879]883 Article No. ct980355
The standard molar enthalpies of formation of SrTeO 3 and SrTe 2 O5 R. Mishra, S. R. Bharadwaj, A. S. Kerkar, and S. R. Dharwadkar a Applied Chemistry Di¨ ision, Bhabha Atomic Research Centre, Trombay, Mumbai-400 085, India
The molar enthalpies of solution of SrTeO3 , SrTe 2 O5 , TeO 2 , and SrCO 3 in HCl Žaq, c s 11 mol . dmy3 . have been measured by using an isoperibol calorimeter. From these Ž . results and other auxiliary data, the standard molar enthalpies of formation D f HT m 298.15 K of SrTeO 3 Žcr. and SrTe 2 O5 Žcr. have been calculated to be yŽ1026.0 " 10.7. kJ . moly1 and yŽ1381.2 " 12.9. kJ . moly1 , respectively. These values of enthalpies of formation are consistent with the second-law enthalpies of formation derived from their vapour pressures determined in this laboratory by a transpiration technique. Q 1998 Academic Press KEYWORDS: enthalpies of formation; solution calorimetry; isoperibol calorimetry; strontium tellurites; SrTeO 3 ; SrTe 2 O5
1. Introduction The thermochemistry of compounds formed as a result of interactions of fission products with the fuel and the clad plays an important role in the prediction of the long-term integrity of nuclear fuel under irradiation.Ž1 ] 3. The thermochemistry of ternary compounds of tellurium, an important fission product, with other fission products and clad materials are of considerable interest. In this context, the standard molar enthalpies of formation D f HT m of the ternary compounds in Žalkaline earth q tellurium q oxygen. are being determined in our laboratory by means of solution calorimetry. Alkaline earth elements such as Sr and Ba are important fission products. Enthalpies of formation of CaTeO 3 and CaTe 2 O5 were investigated Ž4. as a prelude to the study of other compounds formed in Žalkaline earth q tellurium q oxygen. and to investigate possible systematic trends in their thermodynamic stabilities. In this paper, we report the values of the enthalpies of formation of strontium tellurites determined by isoperibol calorimetry. a
ŽE-mail: [email protected]..
0021]9614r98r070879 q 05 $30.00r0
Q 1998 Academic Press
880
R. Mishra et al.
2. Experimental The compounds SrTeO 3 and SrTe 2 O5 were prepared by heating thoroughly ground mixtures of SrCO 3 Žmass fraction 0.99995, Aldrich, U.S.A.. and TeO 2 Žmass fraction 0.99995, Aldrich, U.S.A. in the mole ratios nŽSrCO 3 .rnŽTeO 2 . s 1 and nŽSrCO 3 .rnŽTeO 2 . s 0.5, respectively. The compound SrTeO 3 was prepared by heating thoroughly ground mixtures with nŽSrCO 3 .rnŽTeO 2 . s 1 contained in a platinum boat in flowing argon for 8 h at T s 925 K, followed by heating at T s 1200 K for 30 min. The SrTe 2 O5 was prepared by heating a mixture with nŽSrCO 3 .rnŽTeO 2 . s 0.5 at T s 1000 K under similar conditions. The procedure involved heating the mixture at 0.033 K . sy1 to the required maximum temperatures, followed by isothermal heating for 8 h. The mixtures maintained at these temperatures were withdrawn intermittently from the furnace and reheated after repeated grinding. The completion of the reaction was confirmed by the X-ray powder diffraction patterns of the products. Differential thermal analysis results obtained in this laboratory Ž5. show that SrTeO 3 undergoes two reversible crystallographic transformations around the temperatures T s 1105 K and T s 1246 K. In addition, SrTe 2 O5 undergoes a reversible phase transition at T s 894 K. The reverse transformations in SrTeO 3 are quite slow and are accompanied by considerable temperature hysteresis. The room-temperature phase obtained depends very much on the method of preparation, that is, the maximum temperature to which the reaction mixture is heated and the rate at which the product is cooled. The X-ray diffraction powder patterns of SrTeO 3 prepared for the present work agreed with the pattern reported by Malyutin et al.Ž6. for SrTeO 3 which was obtained by dehydrating SrTeO 3 . H 2 O at T s 603 K. The diffraction pattern of SrTe 2 O5 prepared for the present work agreed with that reported in JCPDS X-ray diffraction file No. 43-344. The chemical analysis of the products was done to confirm that there was no significant change in the stoichiometry of the mixture due to partial vaporization of TeO 2 on prolonged heating. Strontium was determined by gravimetry. The observed Sr contents for the compounds of SrTeO 3 and SrTe 2 O5 were mass fractions Ž0.331 " 0.002. and Ž0.209 " 0.002. as against the calculated values of 0.333 and 0.207, respectively. The Te content was determined by atomic absorption spectroscopy. The observed Te contents in SrTeO 3 and SrTe 2 O5 were mass fractions Ž0.485 " 0.005. and Ž0.601 " 0.005. as against the calculated values of 0.485 and 0.604, respectively. The compounds were prepared by heating the reaction mixtures in flowing argon. Therefore, the oxidation state of Te in these compounds is TeŽIV.. The compounds with TeŽVI. have been reported to be formed only when the mixtures are heated in air or oxygenŽ7. and have distinct X-ray patterns. Even the most prominent X-ray diffraction lines of the compounds with TeŽVI. were absent in the patterns of the compounds prepared in this work. The enthalpies of solution were measured in an isoperibol calorimeter operated at T s 298.15 K. The description of the instrument and the procedures for calibration and measurement have already been reported.Ž8, 9. The calorimeter performance was tested with N.I.S.T. KCl ŽSRM 1655..Ž10. The molar enthalpy of
D f HT m of SrTeO 3 and SrTe 2 O5
881
solution of KCl in distilled water at infinite dilution was: D sol Hm` ŽKCl, 298.15 K. s Ž17.18 " 0.07. kJ . moly1 as against the N.I.S.T. recommended value of Ž17.241 " 0.018. kJ . moly1 . The calorimeter performance was also tested with N.I.S.T. tris trisŽhydroxy methyl.aminomethane4 . Tris was dissolved in 0.150 dm3 of HCl Žaq, c s 0.100 mol . dmy3 . and the enthalpy of dissolution at a concentration of 5 g . dm3 was yŽ29.75 " 0.02. kJ . moly1 , which is in agreement with the N.I.S.T. value of yŽ29.770 " 0.032. kJ . moly1 . The solvent used for the dissolution experiments was 0.150 dm3 of HCl Žaq, c s 11 mol . dmy3 .. The glass bulb containing the sample was equilibrated in the calorimetric solution and was broken to introduce the sample into the solution only after a steady-state signal was obtained on the strip chart recorder. The energy equivalent of the calorimeter was determined before and
TABLE 1. The molar enthalpies of solution D sol Hm of SrTeO3 Žcr., SrTe 2 O5 Žcr., SrCO 3 Žcr., and TeO 2 Žcr. in HCl Žaq, c s 11 mol . dmy3 . at T s 298.15 K; m denotes the mass of sample, D H the experimental enthalpy change, D sol Hm the enthalpy of solution and M the molar mass mrg
D HrJ
SrTeO3 Žcr. Ž M s 263.2182 g . moly1 .
0.0618 0.0733 0.0645 0.0666
y50.47 y59.97 y52.55 y54.59
SrTe 2 O5 Žcr. Ž M s 422.817 g . moly1 .
0.0733 0.0778 0.0867 0.0664
y41.19 y43.52 y48.58 y37.01
TeO 2 Žcr. Ž M s 159.5988 g . moly1 .
0.2137 0.1413 0.1041 0.2206
y68.75 y45.47 y34.58 y71.81
SrCO 3 Žcr. Ž M s 147.6292 g . moly1 .
0.1054 0.0860 0.1031 0.1144
y20.06 y15.61 y19.43 y21.23
Sample
D sol Hm rŽkJ . moly1 .a
y215.0 y215.4 y214.5 y215.8 ² D sol Hm : s yŽ215.2 " 0.6. kJ . moly1 b y237.6 y236.5 y236.9 y235.7 ² D sol Hm : s yŽ236.7 " 0.8. kJ . moly1b y51.3 y51.4 y53.0 y52.0 ² D sol Hm : s yŽ51.9 " 0.8. kJ . moly1 b
y28.1 y26.8 y27.8 y27.4 ² D sol Hm : s yŽ27.5 " 0.6. kJ . moly1 b D Hm ŽCO 2 . s yŽ4.5 " 2.0. kJ . moly1 c Corrected ² D sol Hm : s yŽ32.0 " 2.1. kJ . moly1
a Correction for evaporation of water was calculated as follows: the equilibrium vapour pressure pŽHCl, g. f 10.7 kPa in 11 mol . dmy3 HCl.Ž15. Each bulb containing the sample was assumed to have an internal volume of 1 cm3. For calculation of D vap H the data were taken from the International Critical Tables.Ž15. The correction is less than 0.05 kJ . moly1 . b Average value; uncertainties are twice the standard deviations of the mean. c Correction for evolution of CO 2 was calculated as follows: it was assumed that the CO 2 Žg. was saturated with HCl vapour at the partial pressures given in the International Critical Tables.Ž15. The correction amounts to 4.5 kJ . moly1 , assuming that the stoichiometric amount of CO 2 was evolved and was saturated with the solvent. We have no proof for this. Therefore, the correction is given an uncertainty of "2.0 kJ . moly1 .
882
R. Mishra et al.
TABLE 2. Reaction scheme ŽT s 298.15 K. for the standard molar enthalpy of formation of SrTeO 3 Žcr.: Ž . Ž . Ž . Ž . Ž . Ž . Ž . Ž . D f HT m SrTeO 3 , cr s D H 7 s yDH 1 q DH 2 q DH 3 q DH 4 q DH 5 q DH 6 D Hm rŽkJ . moly1 .
Reaction 1. SrTeO 3 Žcr. q 6HClŽsln. a s ŽSrCl 2 q TeCl 4 q 3H 2 O.Žsln. 2. SrCO 3 Žcr. q 2HClŽsln. s ŽSrCl 2 q H 2 O.Žsln. q CO 2 Žg. 3. TeO 2 Žcr. q 4HClŽsln. s ŽTeCl 4 q 2H 2 O.Žsln. 4. SrŽcr. q CŽcr, graphite. q Ž3r2.O 2 Žg. s SrCO 3 Žcr. 5. TeŽcr. q O 2 Žg. s TeO 2 Žcr. 6. CO 2 Žg. s CŽcr, graphite. q O 2 Žg.
y215.2 " 0.6 y32.0 " 2.1 y51.9 " 0.8 y1226.0 " 10.0 y324.8 " 3.0 393.5 " 0.1
7. SrŽcr. q TeŽcr. q Ž3r2.O 2 Žg. s SrTeO3 Žcr.
y1026.0 " 10.7
a
HClŽsln. denotes HCl Žaq, c s 11 mol . dmy3 ..
after each measurement by electrical calibration with a standard resistance. The temperature change during the reaction was corrected by the method of Kubaschewski and Alcock Ž11. and was used for the evaluation of the enthalpy change of the reaction. A correction for vaporization of the solvent was applied in all cases, and a correction due to evolution of CO 2 was applied in the case of SrCO 3 dissolution.
3. Results and discussion The results of the enthalpies of solution of SrTeO 3 , SrTe 2 O5 , SrCO 3 , and TeO 2 in 0.150 dm3 of HCl Žaq, c s 11 mol ? dmy3 . are given in table 1. Here, m denotes the mass of the sample dissolved, D H is the measured energy change, and D sol Hm is the molar enthalpy of solution. The thermochemical cycles from which the standard molar enthalpies of formation of SrTeO 3 Žcr. and SrTe 2 O5 Žcr. have been derived are given in tables 2 and 3. The molar enthalpies of solution of SrTeO 3 Žcr., SrTe 2 O5 Žcr., SrCO 3 Žcr., and TeO 2 Žcr. in HCl Žaq, c s 11 mol . dmy3 . have been measured to be yŽ215.2 " 0.6. kJ . moly1 , yŽ236.7 " 0.8. kJ . moly1 , yŽ32.0 " 2.1. kJ . moly1 , and yŽ51.9 " 0.8. kJ . moly1 , respectively. These values have been TABLE 3. Reaction scheme ŽT s 298.15 K. for the standard molar enthalpy of formation of Ž . Ž . Ž . Ž . Ž . Ž . Ž . Ž . SrTe 2 O5 Žcr.: D f HT m SrTe 2 O5 , cr s D H 7 s yDH 1 q DH 2 q DH 3 q DH 4 q DH 5 q DH 6 Reaction
D Hm rŽkJ . moly1 .
1. SrTe 2 O5 Žcr. q 10HClŽsln. a s ŽSrCl 2 q 2TeCl 4 q 5H 2 O.Žsln. 2. SrCO 3 Žcr. q 2HClŽsln. s ŽSrCl 2 q H 2 O.Žsln. q CO 2 Žg. 3. 2TeO 2 Žcr. q 8HClŽsln. s Ž2TeCl 4 q 4H 2 O.Žsln. 4. SrŽcr. q CŽcr, graphite. q Ž3r2.O 2 Žg. s SrCO 3 Žcr. 5. 2TeŽcr. q 2O 2 Žg. s 2TeO 2 Žcr. 6. CO 2 Žg. s CŽcr, graphite. q O 2 Žg.
y236.7 " 0.8 y32.0 " 2.1 y103.8 " 1.6 y1226.0 " 10.0 y649.6 " 6.0 393.5 " 0.1
7. SrŽcr. q 2TeŽcr. q Ž5r2.O 2 Žg. s SrTe 2 O5 Žcr.
y1381.2 " 12.0
a
HClŽsln. denotes HCl Žaq, c s 11 mol . dmy3 ..
D f HT m of SrTeO 3 and SrTe 2 O5
883
combined with other auxiliary data such as the standard molar enthalpies of formation of SrCO 3 Žcr., yŽ1226.0 " 10.0. kJ . moly1 ;Ž12. TeO 2 Žcr., yŽ324.8 " 3.0. kJ . moly1 ;Ž12. and CO 2 Žg., yŽ393.5 " 0.1. kJ . moly1 Ž13. to derive the standard molar enthalpies of formation of SrTeO 3 Žcr. s yŽ1026.0 " 10.7. kJ . moly1 and of SrTe 2 O5 Žcr. s yŽ1381.2 " 12.0. kJ . moly1 . There are no previous reports on these quantities. These values of the molar enthalpies of formation of SrTeO 3 and SrTe 2 O5 are consistent with the second-law enthalpies of formation determined in this laboratory by a transpiration technique: yŽ1016.4 " 10.0. kJ . moly1 and yŽ1373.3 " 12.3. kJ . moly1 , respectively.Ž14. Thanks are due to Dr ŽMs. A. C. Udas of Analytical Chemistry Division, BARC for her help in the chemical analysis of the samples. REFERENCES 1. Kleykamp, H. J. Nucl. Mater. 1985, 131, 221]246. 2. Cordfunke, E. H. P.; Konings, R. J. M. J. Nucl. Mater. 1988, 152, 301]309. 3. Potter, P. E. Proceedings of the International Symposium on Thermochemistry and Chemical Processing. Mathews, C. K.: editor. IGCAR: Kalpakkam, India. 1989, pp. 107]129. 4. Mishra, R.; Bharadwaj, S. R.; Dharwadkar, S. R.; Savant, S. S.; Kalyanaraman, R. J. Chem. Thermodynamics 1997, 29, 1087]1091. 5. Mishra, R. Ph.D. Thesis Žto be submitted to Bombay University.. 6. Malyutin, S. A.; Samplavskaya, K. K.; Karapet’yants, M. Kh. Russ. J. Inorg. Chem. 1971, 16, 796]798. 7. JCPDS File Nos 33]1352 and 35-0991. 8. Athavale, V. T.; Kalyanaraman, R.; Sundaresan, M. Ind. J. Chem. 1969, 7, 386]391. 9. Awasthi, S. P.; Sundaresan, M. Ind. J. Chem. 1981, 20A, 378]381. 10. Bharadwaj, S. R.; Samant, M. S.; Mishra, R.; Dharwadkar, S. R.; Sawant, S. S.; Kalyanaraman, R. J. Chem. Thermodynamics 1995, 27, 863]866. 11. Kubaschewski, O.; Alcock, C. B. Metallurgical Thermochemistry: 5th edition. Pergamon: Oxford. 1979. 12. IVTAN Thermochemical Data ŽFrom tabular data send by Dr P. A. G. O’Hare.. 13. Cox, J. D.; Wagman, D. D.; Medvedev, V. A. CODATA Key Values for Thermodynamics. Hemisphere: New York. 1989. 14. Mishra, R.; Bharadwaj, S. R.; Kerkar, A. S.; Dharwadkar, S. R. J. Nucl. Mater. Žin press.. 15. International Critical Tables, Vol. III. Washburn, R. G.; West, C. J.; Dorsey, N. E.; Bichowsky, F. R.; Klemenc, A. D.: editors. McGraw-Hill: New York. 1928.
(Recei¨ ed 22 October 1997; in final form 9 February 1998)
O-706
The standard molar enthalpies of formation of SrTeO 3 and SrTe 2 O5 R. Mishra, S. R. Bharadwaj, A. S. Kerkar, and S. R. Dharwadkar a Applied Chemistry Di¨ ision, Bhabha Atomic Research Centre, Trombay, Mumbai-400 085, India
The molar enthalpies of solution of SrTeO3 , SrTe 2 O5 , TeO 2 , and SrCO 3 in HCl Žaq, c s 11 mol . dmy3 . have been measured by using an isoperibol calorimeter. From these Ž . results and other auxiliary data, the standard molar enthalpies of formation D f HT m 298.15 K of SrTeO 3 Žcr. and SrTe 2 O5 Žcr. have been calculated to be yŽ1026.0 " 10.7. kJ . moly1 and yŽ1381.2 " 12.9. kJ . moly1 , respectively. These values of enthalpies of formation are consistent with the second-law enthalpies of formation derived from their vapour pressures determined in this laboratory by a transpiration technique. Q 1998 Academic Press KEYWORDS: enthalpies of formation; solution calorimetry; isoperibol calorimetry; strontium tellurites; SrTeO 3 ; SrTe 2 O5
1. Introduction The thermochemistry of compounds formed as a result of interactions of fission products with the fuel and the clad plays an important role in the prediction of the long-term integrity of nuclear fuel under irradiation.Ž1 ] 3. The thermochemistry of ternary compounds of tellurium, an important fission product, with other fission products and clad materials are of considerable interest. In this context, the standard molar enthalpies of formation D f HT m of the ternary compounds in Žalkaline earth q tellurium q oxygen. are being determined in our laboratory by means of solution calorimetry. Alkaline earth elements such as Sr and Ba are important fission products. Enthalpies of formation of CaTeO 3 and CaTe 2 O5 were investigated Ž4. as a prelude to the study of other compounds formed in Žalkaline earth q tellurium q oxygen. and to investigate possible systematic trends in their thermodynamic stabilities. In this paper, we report the values of the enthalpies of formation of strontium tellurites determined by isoperibol calorimetry. a
ŽE-mail: [email protected]..
0021]9614r98r070879 q 05 $30.00r0
Q 1998 Academic Press
880
R. Mishra et al.
2. Experimental The compounds SrTeO 3 and SrTe 2 O5 were prepared by heating thoroughly ground mixtures of SrCO 3 Žmass fraction 0.99995, Aldrich, U.S.A.. and TeO 2 Žmass fraction 0.99995, Aldrich, U.S.A. in the mole ratios nŽSrCO 3 .rnŽTeO 2 . s 1 and nŽSrCO 3 .rnŽTeO 2 . s 0.5, respectively. The compound SrTeO 3 was prepared by heating thoroughly ground mixtures with nŽSrCO 3 .rnŽTeO 2 . s 1 contained in a platinum boat in flowing argon for 8 h at T s 925 K, followed by heating at T s 1200 K for 30 min. The SrTe 2 O5 was prepared by heating a mixture with nŽSrCO 3 .rnŽTeO 2 . s 0.5 at T s 1000 K under similar conditions. The procedure involved heating the mixture at 0.033 K . sy1 to the required maximum temperatures, followed by isothermal heating for 8 h. The mixtures maintained at these temperatures were withdrawn intermittently from the furnace and reheated after repeated grinding. The completion of the reaction was confirmed by the X-ray powder diffraction patterns of the products. Differential thermal analysis results obtained in this laboratory Ž5. show that SrTeO 3 undergoes two reversible crystallographic transformations around the temperatures T s 1105 K and T s 1246 K. In addition, SrTe 2 O5 undergoes a reversible phase transition at T s 894 K. The reverse transformations in SrTeO 3 are quite slow and are accompanied by considerable temperature hysteresis. The room-temperature phase obtained depends very much on the method of preparation, that is, the maximum temperature to which the reaction mixture is heated and the rate at which the product is cooled. The X-ray diffraction powder patterns of SrTeO 3 prepared for the present work agreed with the pattern reported by Malyutin et al.Ž6. for SrTeO 3 which was obtained by dehydrating SrTeO 3 . H 2 O at T s 603 K. The diffraction pattern of SrTe 2 O5 prepared for the present work agreed with that reported in JCPDS X-ray diffraction file No. 43-344. The chemical analysis of the products was done to confirm that there was no significant change in the stoichiometry of the mixture due to partial vaporization of TeO 2 on prolonged heating. Strontium was determined by gravimetry. The observed Sr contents for the compounds of SrTeO 3 and SrTe 2 O5 were mass fractions Ž0.331 " 0.002. and Ž0.209 " 0.002. as against the calculated values of 0.333 and 0.207, respectively. The Te content was determined by atomic absorption spectroscopy. The observed Te contents in SrTeO 3 and SrTe 2 O5 were mass fractions Ž0.485 " 0.005. and Ž0.601 " 0.005. as against the calculated values of 0.485 and 0.604, respectively. The compounds were prepared by heating the reaction mixtures in flowing argon. Therefore, the oxidation state of Te in these compounds is TeŽIV.. The compounds with TeŽVI. have been reported to be formed only when the mixtures are heated in air or oxygenŽ7. and have distinct X-ray patterns. Even the most prominent X-ray diffraction lines of the compounds with TeŽVI. were absent in the patterns of the compounds prepared in this work. The enthalpies of solution were measured in an isoperibol calorimeter operated at T s 298.15 K. The description of the instrument and the procedures for calibration and measurement have already been reported.Ž8, 9. The calorimeter performance was tested with N.I.S.T. KCl ŽSRM 1655..Ž10. The molar enthalpy of
D f HT m of SrTeO 3 and SrTe 2 O5
881
solution of KCl in distilled water at infinite dilution was: D sol Hm` ŽKCl, 298.15 K. s Ž17.18 " 0.07. kJ . moly1 as against the N.I.S.T. recommended value of Ž17.241 " 0.018. kJ . moly1 . The calorimeter performance was also tested with N.I.S.T. tris trisŽhydroxy methyl.aminomethane4 . Tris was dissolved in 0.150 dm3 of HCl Žaq, c s 0.100 mol . dmy3 . and the enthalpy of dissolution at a concentration of 5 g . dm3 was yŽ29.75 " 0.02. kJ . moly1 , which is in agreement with the N.I.S.T. value of yŽ29.770 " 0.032. kJ . moly1 . The solvent used for the dissolution experiments was 0.150 dm3 of HCl Žaq, c s 11 mol . dmy3 .. The glass bulb containing the sample was equilibrated in the calorimetric solution and was broken to introduce the sample into the solution only after a steady-state signal was obtained on the strip chart recorder. The energy equivalent of the calorimeter was determined before and
TABLE 1. The molar enthalpies of solution D sol Hm of SrTeO3 Žcr., SrTe 2 O5 Žcr., SrCO 3 Žcr., and TeO 2 Žcr. in HCl Žaq, c s 11 mol . dmy3 . at T s 298.15 K; m denotes the mass of sample, D H the experimental enthalpy change, D sol Hm the enthalpy of solution and M the molar mass mrg
D HrJ
SrTeO3 Žcr. Ž M s 263.2182 g . moly1 .
0.0618 0.0733 0.0645 0.0666
y50.47 y59.97 y52.55 y54.59
SrTe 2 O5 Žcr. Ž M s 422.817 g . moly1 .
0.0733 0.0778 0.0867 0.0664
y41.19 y43.52 y48.58 y37.01
TeO 2 Žcr. Ž M s 159.5988 g . moly1 .
0.2137 0.1413 0.1041 0.2206
y68.75 y45.47 y34.58 y71.81
SrCO 3 Žcr. Ž M s 147.6292 g . moly1 .
0.1054 0.0860 0.1031 0.1144
y20.06 y15.61 y19.43 y21.23
Sample
D sol Hm rŽkJ . moly1 .a
y215.0 y215.4 y214.5 y215.8 ² D sol Hm : s yŽ215.2 " 0.6. kJ . moly1 b y237.6 y236.5 y236.9 y235.7 ² D sol Hm : s yŽ236.7 " 0.8. kJ . moly1b y51.3 y51.4 y53.0 y52.0 ² D sol Hm : s yŽ51.9 " 0.8. kJ . moly1 b
y28.1 y26.8 y27.8 y27.4 ² D sol Hm : s yŽ27.5 " 0.6. kJ . moly1 b D Hm ŽCO 2 . s yŽ4.5 " 2.0. kJ . moly1 c Corrected ² D sol Hm : s yŽ32.0 " 2.1. kJ . moly1
a Correction for evaporation of water was calculated as follows: the equilibrium vapour pressure pŽHCl, g. f 10.7 kPa in 11 mol . dmy3 HCl.Ž15. Each bulb containing the sample was assumed to have an internal volume of 1 cm3. For calculation of D vap H the data were taken from the International Critical Tables.Ž15. The correction is less than 0.05 kJ . moly1 . b Average value; uncertainties are twice the standard deviations of the mean. c Correction for evolution of CO 2 was calculated as follows: it was assumed that the CO 2 Žg. was saturated with HCl vapour at the partial pressures given in the International Critical Tables.Ž15. The correction amounts to 4.5 kJ . moly1 , assuming that the stoichiometric amount of CO 2 was evolved and was saturated with the solvent. We have no proof for this. Therefore, the correction is given an uncertainty of "2.0 kJ . moly1 .
882
R. Mishra et al.
TABLE 2. Reaction scheme ŽT s 298.15 K. for the standard molar enthalpy of formation of SrTeO 3 Žcr.: Ž . Ž . Ž . Ž . Ž . Ž . Ž . Ž . D f HT m SrTeO 3 , cr s D H 7 s yDH 1 q DH 2 q DH 3 q DH 4 q DH 5 q DH 6 D Hm rŽkJ . moly1 .
Reaction 1. SrTeO 3 Žcr. q 6HClŽsln. a s ŽSrCl 2 q TeCl 4 q 3H 2 O.Žsln. 2. SrCO 3 Žcr. q 2HClŽsln. s ŽSrCl 2 q H 2 O.Žsln. q CO 2 Žg. 3. TeO 2 Žcr. q 4HClŽsln. s ŽTeCl 4 q 2H 2 O.Žsln. 4. SrŽcr. q CŽcr, graphite. q Ž3r2.O 2 Žg. s SrCO 3 Žcr. 5. TeŽcr. q O 2 Žg. s TeO 2 Žcr. 6. CO 2 Žg. s CŽcr, graphite. q O 2 Žg.
y215.2 " 0.6 y32.0 " 2.1 y51.9 " 0.8 y1226.0 " 10.0 y324.8 " 3.0 393.5 " 0.1
7. SrŽcr. q TeŽcr. q Ž3r2.O 2 Žg. s SrTeO3 Žcr.
y1026.0 " 10.7
a
HClŽsln. denotes HCl Žaq, c s 11 mol . dmy3 ..
after each measurement by electrical calibration with a standard resistance. The temperature change during the reaction was corrected by the method of Kubaschewski and Alcock Ž11. and was used for the evaluation of the enthalpy change of the reaction. A correction for vaporization of the solvent was applied in all cases, and a correction due to evolution of CO 2 was applied in the case of SrCO 3 dissolution.
3. Results and discussion The results of the enthalpies of solution of SrTeO 3 , SrTe 2 O5 , SrCO 3 , and TeO 2 in 0.150 dm3 of HCl Žaq, c s 11 mol ? dmy3 . are given in table 1. Here, m denotes the mass of the sample dissolved, D H is the measured energy change, and D sol Hm is the molar enthalpy of solution. The thermochemical cycles from which the standard molar enthalpies of formation of SrTeO 3 Žcr. and SrTe 2 O5 Žcr. have been derived are given in tables 2 and 3. The molar enthalpies of solution of SrTeO 3 Žcr., SrTe 2 O5 Žcr., SrCO 3 Žcr., and TeO 2 Žcr. in HCl Žaq, c s 11 mol . dmy3 . have been measured to be yŽ215.2 " 0.6. kJ . moly1 , yŽ236.7 " 0.8. kJ . moly1 , yŽ32.0 " 2.1. kJ . moly1 , and yŽ51.9 " 0.8. kJ . moly1 , respectively. These values have been TABLE 3. Reaction scheme ŽT s 298.15 K. for the standard molar enthalpy of formation of Ž . Ž . Ž . Ž . Ž . Ž . Ž . Ž . SrTe 2 O5 Žcr.: D f HT m SrTe 2 O5 , cr s D H 7 s yDH 1 q DH 2 q DH 3 q DH 4 q DH 5 q DH 6 Reaction
D Hm rŽkJ . moly1 .
1. SrTe 2 O5 Žcr. q 10HClŽsln. a s ŽSrCl 2 q 2TeCl 4 q 5H 2 O.Žsln. 2. SrCO 3 Žcr. q 2HClŽsln. s ŽSrCl 2 q H 2 O.Žsln. q CO 2 Žg. 3. 2TeO 2 Žcr. q 8HClŽsln. s Ž2TeCl 4 q 4H 2 O.Žsln. 4. SrŽcr. q CŽcr, graphite. q Ž3r2.O 2 Žg. s SrCO 3 Žcr. 5. 2TeŽcr. q 2O 2 Žg. s 2TeO 2 Žcr. 6. CO 2 Žg. s CŽcr, graphite. q O 2 Žg.
y236.7 " 0.8 y32.0 " 2.1 y103.8 " 1.6 y1226.0 " 10.0 y649.6 " 6.0 393.5 " 0.1
7. SrŽcr. q 2TeŽcr. q Ž5r2.O 2 Žg. s SrTe 2 O5 Žcr.
y1381.2 " 12.0
a
HClŽsln. denotes HCl Žaq, c s 11 mol . dmy3 ..
D f HT m of SrTeO 3 and SrTe 2 O5
883
combined with other auxiliary data such as the standard molar enthalpies of formation of SrCO 3 Žcr., yŽ1226.0 " 10.0. kJ . moly1 ;Ž12. TeO 2 Žcr., yŽ324.8 " 3.0. kJ . moly1 ;Ž12. and CO 2 Žg., yŽ393.5 " 0.1. kJ . moly1 Ž13. to derive the standard molar enthalpies of formation of SrTeO 3 Žcr. s yŽ1026.0 " 10.7. kJ . moly1 and of SrTe 2 O5 Žcr. s yŽ1381.2 " 12.0. kJ . moly1 . There are no previous reports on these quantities. These values of the molar enthalpies of formation of SrTeO 3 and SrTe 2 O5 are consistent with the second-law enthalpies of formation determined in this laboratory by a transpiration technique: yŽ1016.4 " 10.0. kJ . moly1 and yŽ1373.3 " 12.3. kJ . moly1 , respectively.Ž14. Thanks are due to Dr ŽMs. A. C. Udas of Analytical Chemistry Division, BARC for her help in the chemical analysis of the samples. REFERENCES 1. Kleykamp, H. J. Nucl. Mater. 1985, 131, 221]246. 2. Cordfunke, E. H. P.; Konings, R. J. M. J. Nucl. Mater. 1988, 152, 301]309. 3. Potter, P. E. Proceedings of the International Symposium on Thermochemistry and Chemical Processing. Mathews, C. K.: editor. IGCAR: Kalpakkam, India. 1989, pp. 107]129. 4. Mishra, R.; Bharadwaj, S. R.; Dharwadkar, S. R.; Savant, S. S.; Kalyanaraman, R. J. Chem. Thermodynamics 1997, 29, 1087]1091. 5. Mishra, R. Ph.D. Thesis Žto be submitted to Bombay University.. 6. Malyutin, S. A.; Samplavskaya, K. K.; Karapet’yants, M. Kh. Russ. J. Inorg. Chem. 1971, 16, 796]798. 7. JCPDS File Nos 33]1352 and 35-0991. 8. Athavale, V. T.; Kalyanaraman, R.; Sundaresan, M. Ind. J. Chem. 1969, 7, 386]391. 9. Awasthi, S. P.; Sundaresan, M. Ind. J. Chem. 1981, 20A, 378]381. 10. Bharadwaj, S. R.; Samant, M. S.; Mishra, R.; Dharwadkar, S. R.; Sawant, S. S.; Kalyanaraman, R. J. Chem. Thermodynamics 1995, 27, 863]866. 11. Kubaschewski, O.; Alcock, C. B. Metallurgical Thermochemistry: 5th edition. Pergamon: Oxford. 1979. 12. IVTAN Thermochemical Data ŽFrom tabular data send by Dr P. A. G. O’Hare.. 13. Cox, J. D.; Wagman, D. D.; Medvedev, V. A. CODATA Key Values for Thermodynamics. Hemisphere: New York. 1989. 14. Mishra, R.; Bharadwaj, S. R.; Kerkar, A. S.; Dharwadkar, S. R. J. Nucl. Mater. Žin press.. 15. International Critical Tables, Vol. III. Washburn, R. G.; West, C. J.; Dorsey, N. E.; Bichowsky, F. R.; Klemenc, A. D.: editors. McGraw-Hill: New York. 1928.
(Recei¨ ed 22 October 1997; in final form 9 February 1998)
O-706