重铬酸钾晶体低温热容及热力学性质的研究

用精密自动绝热量热计测定了重铬酸钾晶体在100～390 K温区内的摩尔热容.实验结果表明在研究温度区间内重铬酸钾无相变和其它热反常现象发生,但其热容在不同的温度范围表现出不同的变化趋势.在100 K≤ T ≤ 275 K和350 K≤ T ≤390 K区间内,其热容随温度的升高明显增大,在275 K≤ T ≤350 K区间,其热容约为定值.将重铬酸钾摩尔热容实验值Cp,m(J?K－1?mol－1)拟合成温度T的多项式方程,在100 K≤ T ≤275 K,为Cp,m=0.0050T2－1.0320T＋125.22； 275 K≤ T ≤ 350 K,为Cp,m=209.37； 350 K≤ T ≤390 K,为Cp,m= 0.0266T2－18.823T＋3542.3.根据热力学函数关系式,从热容值计算出了298.15 K～ 400 K温区范围内每隔5 K的热力学函数值.

Low Temperature Heat Capacities and Thermodynamic Functions of Potassium Dichromate

The molar heat capacities (Cp,m) of crystalline potassium dichromate (K2Cr2O7) were measured with a precision automated adiabatic calorimeter over the temperature range from 100 K to 390 K. No phase transition or other thermal anomaly was observed in this temperature region. However, it was found that the relationship of Cp,m with respect to temperature T is different in different temperature regions. The polynomial functions of Cp,m vs. T were established in different temperature regions based on the heat capacity measurements by means of the least-fitting square method. These functions are as following: for 100 K ≤ T ≤ 275 K, Cp,m=0.0050T2－1.0320T＋125.22 (J?K－1?mol－1)；for 275 K ≤ T ≤ 350 K, Cp,m=209.37 J?K－1?mol－1；for 350 K ≤ T ≤390 K, Cp,m=0.0266T2－18.823T＋3542.3 J?K－1?mol－1.According to the relationship of Cp,m vs. T and thermodynamic equations, the values of thermodynamic function of potassium dichromate were calculated in the temperature range of 298.15～400.15 K with 5 K intervals.