硼砂水溶液的低温热容及热化学性质研究

利用精密绝热量热仪测定了0.03355mol·kg-1的硼砂水溶液在78～351K温区的热容,从实验热容测定结果得到了该水溶液的凝固点为272.905K。用最小二乘法将实验热容值对温度进行拟合,建立了该溶液的热容随温度变化的多项式方程。根据热力学函数关系式,用此多项式方程进行数值积分,获得了以298.15K为基准的该溶液在80～350K温区每隔5K的热力学函数值,并计算出摩尔熔化焓和熔化熵分别为4.536kJ·mol-1和16.22J·K-1·mol-1。根据溶液凝固点降低值,计算出了该溶液的活度为0.99763。

Low-Temperature Heat Capacities and Thermodynamic Properties of Aqueous Na2B4O7 Solution

The molar heat capacities of aqueous Na₂B₄O₇ solution with concentration of 0.033 55 mol·kg^-1 were measured by a precision automated adiabatic calorimeter in the temperature range from 78 K to 351 K. The fusion transition at T=272.905 K was observed from the heat capacity measurements. According to the polynomial equations of heat capacity as a function of temperature and thermodynamic relationship, the thermodynamic functions (H_T-H298.15K ) and (S_T-S298.15 K) of the aqueous borax decahydrate solution were derived in the temperature range from about 80 to 350 K with an interval of 5 K. The molar enthalpy and entropy of the phase transition were determined to be 4.536 kJ·mol^-1 and 16.62 J·K^-1·mol^-1. The activity of the solution was determined to be 0.997 63 by using the freezing point depression of the solution based on the liquid-solid phase equilibrium rule.