The solid potassium L-threonate hydrate, K（C4H7O5）·H2O, was synthesized by the reaction of L-threonic acid with aqueous potassium hydrogen carbonate and characterized by means of chemical and elemental analyses...The solid potassium L-threonate hydrate, K（C4H7O5）·H2O, was synthesized by the reaction of L-threonic acid with aqueous potassium hydrogen carbonate and characterized by means of chemical and elemental analyses, IR and TG-DTG. Low-temperature heat capacity of K（C4H7O5）·H2O has been precisely measured with a small sample precise automated adiabatic calorimeter over the temperature range from 78 to 395 K. An obvious process of the dehydration occurred in the temperature region of 364-382 K. The peak temperature of the dehydration of the compound has been observed to be （380.524±0.093） K by means of the heat capacity measurements. The molar enthalpy, △dHm, and molar entropy, △dSm, of the dehydration of K（C4H7O5）·H2O were calculated to be （19.655 ± 0.012） kJ/mol and （51.618 ± 0.051） J/（K·mol） by the analysis of the heat-capacity curve. The experimental molar heat capacities of the solid from 78 to 362 K and from 382 to 395 K have been respectively fitted to two polynomial equations of heat capacities against the reduced temperatures by least square method. The constant-volume energy of combustion of the compound, △cUm, has been determined to be （- 1749.71 ±0.91） kJ·mol^-1 by an RBC-Ⅱ precision rotary-bomb combustion calorimeter at 298.15 K. The standard molar enthalpy of formation of the compound, △fHm , has been calculated to be （- 1292.56± 1.06） kJ·mol^-1 from the combination of the standard molar enthalpy of combustion of the compound with other auxiliary thermodynamic quantities.展开更多
Low-temperature heat capacities of the solid compound NaCuAsO4·1.5H2O（s）were measured using a precision automated adiabatic calorimeter over a temperature range of T=78 K to T=390 K.A dehydration process occurr...Low-temperature heat capacities of the solid compound NaCuAsO4·1.5H2O（s）were measured using a precision automated adiabatic calorimeter over a temperature range of T=78 K to T=390 K.A dehydration process occurred in the temperature range of T=368-374 K.The peak temperature of the dehydration was observed to be TD=（371.828±0.146）K by means of the heat-capacity measurement.The molar enthalpy and entropy of the dehydration were ΔDHm=（18.571±0.142）kJ/mol and ΔDSm=（49.946±0.415）J/（K·mol）,respectively.The experimental values of heat capacities for the solid（Ⅰ）and the solid-liquid mixture（Ⅱ）were respectively fitted to two polynomial equations by the least square method.The smoothed values of the molar heat capacities and the fundamental thermodynamic functions of the sample relative to the standard reference temperature 298.15 K were tabulated at an interval of 5 K.展开更多
An automatic adiabatic calorimeter for measuring heat capacities in the temperature range 70-580K, equipped with a small sample cell of 7.4 cm3 in the internal volume has been developed. In order to obtain a good adia...An automatic adiabatic calorimeter for measuring heat capacities in the temperature range 70-580K, equipped with a small sample cell of 7.4 cm3 in the internal volume has been developed. In order to obtain a good adiabatic condition of the calorimeter at high temperature, the calorimeter was surrounded in sequence by two adiabatic shields, three radiation shields and an auxiliary temperature-controlled sheath. The main body of the cell made of copper and the lid made of brass are silver-soldered and the cell is sealed with a copper screw cap. A sealing gasket made of Pb- Sn alloy is put between the cap and the lid to ensure a high vacuum sealing of the cell in the whole experimental temperature range. All the leads are insulated and fixed with W30-11 varnish, thus a good electric insulation is obtained at high temperature. All the experimental data, including those for energy and temperature are collected and processed automatically with a personal computer using a predetermined program. To verify the accuracy of the calorimeter, the heat capacities of α-Al2O3 of the calorimetric standard reference material is measured. The standard deviations of experimental heat capacity values from the smoothed values are within ±0.28%, while the inaccuracy is within ±0.4% compared with those of the National Bureau of Standards over the entire working temperature range.展开更多
This paper reports that the low-temperature heat capacities of pyridine-2,6-dicarboxylic acid were measured by a precision automatic calorimeter over a temperature range from 78 K to 380 K. A polynomial equation of he...This paper reports that the low-temperature heat capacities of pyridine-2,6-dicarboxylic acid were measured by a precision automatic calorimeter over a temperature range from 78 K to 380 K. A polynomial equation of heat capacities as a function of temperature was fitted by the least-squares method. Based on the fitted polynomial, the smoothed heat capacities and thermodynamic functions of the compound relative to the standard reference temperature 298.15 K were calculated and tabulated at intervals of 5 K. The constant-volume energy of combustion of the compound was determined by means of a precision rotating-bomb combustion calorimeter. The standard molar enthalpy of combustion of the compound was derived from the constant-volume energy of combustion. The standard molar enthalpy of formation of the compound was calculated from a combination of the datum of the standard molar enthalpy of combustion of the compound with other auxiliary thermodynamic quantities through a Hess thermochemical cycle.展开更多
基金Project supported by the National Natural Science Foundation of China （No. 20171036）, Education Committee of Shannxi Province （Nos. 01JK229, FF02328 and 2004B 10） and Postgraduate Foundation of China.
文摘The solid potassium L-threonate hydrate, K（C4H7O5）·H2O, was synthesized by the reaction of L-threonic acid with aqueous potassium hydrogen carbonate and characterized by means of chemical and elemental analyses, IR and TG-DTG. Low-temperature heat capacity of K（C4H7O5）·H2O has been precisely measured with a small sample precise automated adiabatic calorimeter over the temperature range from 78 to 395 K. An obvious process of the dehydration occurred in the temperature region of 364-382 K. The peak temperature of the dehydration of the compound has been observed to be （380.524±0.093） K by means of the heat capacity measurements. The molar enthalpy, △dHm, and molar entropy, △dSm, of the dehydration of K（C4H7O5）·H2O were calculated to be （19.655 ± 0.012） kJ/mol and （51.618 ± 0.051） J/（K·mol） by the analysis of the heat-capacity curve. The experimental molar heat capacities of the solid from 78 to 362 K and from 382 to 395 K have been respectively fitted to two polynomial equations of heat capacities against the reduced temperatures by least square method. The constant-volume energy of combustion of the compound, △cUm, has been determined to be （- 1749.71 ±0.91） kJ·mol^-1 by an RBC-Ⅱ precision rotary-bomb combustion calorimeter at 298.15 K. The standard molar enthalpy of formation of the compound, △fHm , has been calculated to be （- 1292.56± 1.06） kJ·mol^-1 from the combination of the standard molar enthalpy of combustion of the compound with other auxiliary thermodynamic quantities.
基金Supported by the National Natural Science Foundation of China(No.20673050).
文摘Low-temperature heat capacities of the solid compound NaCuAsO4·1.5H2O（s）were measured using a precision automated adiabatic calorimeter over a temperature range of T=78 K to T=390 K.A dehydration process occurred in the temperature range of T=368-374 K.The peak temperature of the dehydration was observed to be TD=（371.828±0.146）K by means of the heat-capacity measurement.The molar enthalpy and entropy of the dehydration were ΔDHm=（18.571±0.142）kJ/mol and ΔDSm=（49.946±0.415）J/（K·mol）,respectively.The experimental values of heat capacities for the solid（Ⅰ）and the solid-liquid mixture（Ⅱ）were respectively fitted to two polynomial equations by the least square method.The smoothed values of the molar heat capacities and the fundamental thermodynamic functions of the sample relative to the standard reference temperature 298.15 K were tabulated at an interval of 5 K.
基金Project supported by the National Natural Science Foundation of China (Grant No. 29573133).
文摘An automatic adiabatic calorimeter for measuring heat capacities in the temperature range 70-580K, equipped with a small sample cell of 7.4 cm3 in the internal volume has been developed. In order to obtain a good adiabatic condition of the calorimeter at high temperature, the calorimeter was surrounded in sequence by two adiabatic shields, three radiation shields and an auxiliary temperature-controlled sheath. The main body of the cell made of copper and the lid made of brass are silver-soldered and the cell is sealed with a copper screw cap. A sealing gasket made of Pb- Sn alloy is put between the cap and the lid to ensure a high vacuum sealing of the cell in the whole experimental temperature range. All the leads are insulated and fixed with W30-11 varnish, thus a good electric insulation is obtained at high temperature. All the experimental data, including those for energy and temperature are collected and processed automatically with a personal computer using a predetermined program. To verify the accuracy of the calorimeter, the heat capacities of α-Al2O3 of the calorimetric standard reference material is measured. The standard deviations of experimental heat capacity values from the smoothed values are within ±0.28%, while the inaccuracy is within ±0.4% compared with those of the National Bureau of Standards over the entire working temperature range.
基金Project supported by the National Natural Science Foundations of China (Grant Nos.20673050 and 20973089)
文摘This paper reports that the low-temperature heat capacities of pyridine-2,6-dicarboxylic acid were measured by a precision automatic calorimeter over a temperature range from 78 K to 380 K. A polynomial equation of heat capacities as a function of temperature was fitted by the least-squares method. Based on the fitted polynomial, the smoothed heat capacities and thermodynamic functions of the compound relative to the standard reference temperature 298.15 K were calculated and tabulated at intervals of 5 K. The constant-volume energy of combustion of the compound was determined by means of a precision rotating-bomb combustion calorimeter. The standard molar enthalpy of combustion of the compound was derived from the constant-volume energy of combustion. The standard molar enthalpy of formation of the compound was calculated from a combination of the datum of the standard molar enthalpy of combustion of the compound with other auxiliary thermodynamic quantities through a Hess thermochemical cycle.
