体系的Cp一定大于CV吗?

Is a Thermodynamic System's Cp Always Greater than Its CV?

通过讨论热力学体系的恒容热容Cp和恒压热容CV之间的关系,结果表明,对无非体积功的组成恒定的均相封闭系统,有Cp-CV=TVα^2/κ成立。对于热力学系统,因为一定有压缩系数κ>0,所以Cp一定不小于CV。在体系温度接近绝对零度时,二者非常接近;T=0K时,二者相等。α的正负不影响二者的关系,不过α=0时二者相等。由于凝聚态体系的CV难以测量,因此可以利用上述关系式方便地获得其值。

The relationship between two heat capacities of thermodynamic systems,Cp and Cp,is thoroughly discussed.The results show that an extremely important equation,Cp-CV=TVα^2/κ,is valid for homogeneously closed systems with fixed composition without non-volume work.Since the compression coefficient κ has been proved to be always positive for stable thermodynamic systems,Cp should not be less than CV.When T→0,Cp and CV are close to each other,whereas when T=0,Cp and CV are identical.The coefficient of thermal expansion α does not influence the relationship Cp>CV,except for the situation α=0.As the CV of a condensed phase is difficult to measure directly,the above equation provides a convenient method to obtain the value of CV.