2-噻吩乙酸的低温热容和热力学性质

用精密自动绝热量热计测定了2-噻吩乙酸在78～343 K温区内的摩尔热容. 实验结果表明, 在78～314和337～343 K温区内, 该化合物无相变及其他热异常现象发生, 将实验数据拟合得到了该化合物热容随温度变化的多项式方程; 在314～337 K温区内, 该物质发生固-液熔化相变, 其熔化温度、熔化焓、熔化熵及样品纯度分别确定为: 335.745 K, 16.260 kJ•mol^－1, 48.415 J•K^－1•mol^－1和98.555%. 根据热力学函数关系式, 由热容数据计算出了2-噻吩乙酸在80～340 K温区内相对于标准参考温度298.15 K的热力学函数值.

Low-temperature Heat Capacity and Thermodynamic Properties of 2-Thiopheneacetic Acid

The low-temperature heat capacity of 2-thiopheneacetic acid was measured in the temperature range from 78 to 343 K with a high precision automated adiabatic calorimeter. No phase transition or other thermal anomaly was observed in the temperature ranges of 78～314 and 337～343 K, in which the molar heat capacities were fitted to two polynomials by means of the least square fitting. A solid-liquid phase tran-sition was observed in the temperature range of 314～337 K. The melting point, molar enthalpy and entropy of fusion, and molar purity of this compound were determined to be 335.745 K, 16.260 kJ·mol~(-1), 48.415 J·K~(-1)·mol~(-1) and 98.56%, respectively. The thermodynamic functions of 2-thiopheneacetic acid relative to the reference temperature 298.15 K were derived based on the heat capacity data in the temperature range of 80～340 K.