The uniqueness of the integration factor associated with the exchanged heat in thermodynamics

Abstract

State functions play important roles in thermodynamics. Different from the process function, such as the exchanged heat δQ and the applied work δW, the change of the state function can be expressed as an exact differential. We prove here that, for a generic thermodynamic system, only the inverse of the temperature, namely 1/T, can serve as the integration factor for the exchanged heat δQ. The uniqueness of the integration factor invalidates any attempt to define other state functions associated with the exchanged heat, and in turn, reveals the incorrectness of defining the entransy Evh=CVT2/2 as a state function by treating T as an integration factor. We further show the errors in the derivation of entransy by treating the heat capacity CV as a temperature-independent constant.

Keywords

• Integration factor
• Process function
• Exchanged heat
• Thermodynamic entropy
• Uniqueness theorem