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Low‐Temperature Heat Capacities and Thermodynamic Properties of Octahydrated Barium Dihydroxide, Ba(OH) 2 ·8H 2 O(s)
Author(s) -
Di YouYing,
Tan ZhiCheng,
Sun LiXian
Publication year - 2007
Publication title -
chinese journal of chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.28
H-Index - 41
eISSN - 1614-7065
pISSN - 1001-604X
DOI - 10.1002/cjoc.200790110
Subject(s) - chemistry , heat capacity , endothermic process , enthalpy , atmospheric temperature range , thermal decomposition , thermodynamics , entropy of fusion , adiabatic process , enthalpy of fusion , calorimetry , thermal analysis , dehydration , melting point , thermal , organic chemistry , adsorption , biochemistry , physics
Low‐temperature heat capacities of octahydrated barium dihydroxide, Ba(OH) 2 ·8H 2 O(s), were measured by a precision automated adiabatic calorimeter in the temperature range from T =78 to 370 K. An obvious endothermic process took place in the temperature range of 345–356 K. The peak in the heat capacity curve was correspondent to the sum of both the fusion and the first thermal decomposition or dehydration. The experimental molar heat capacities in the temperature ranges of 78–345 K and 356–369 K were fitted to two polynomials. The peak temperature, molar enthalpy and entropy of the phase change have been determined to be (355.007±0.076) K, (73.506±0.011) kJ·mol −1 and (207.140±0.074) J·K −1 ·mol −1 , respectively, by three series of repeated heat capacity measurements in the temperature region of 298–370 K. The thermodynamic functions, ( H T − H 298.15 K ) and ( S T − S 298.15 K ), of the compound have been calculated by the numerical integral of the two heat‐capacity polynomials. In addition, DSC and TG‐DTG techniques were used for the further study of thermal behavior of the compound. The latent heat of the phase change became into a value larger than that of the normal compound because the melting process of the compound must be accompanied by the thermal decomposition or dehydration of 7H 2 O.