The chemical affinity and reaction heat are two important parameters for studying the properties of the chemical reactions of thermodynamic systems at low temperatures. It is expounded that for a thermodynamic system only containing volume variable work, the two parameters in the reversible isothermal and isobaric process can be calculated through the thermodynamic theory and both of them are zero. These two parameters must be measured by experiment in the irreversible isothermal and isobaric process and their values depend on the irreversibility of the isothermal and isobaric process, but the relationship between them can be discussed by thermodynamic theory. When the temperature is absolute zero, both of these parameters are zero. Some examples given in textbooks and literature are debatable.

According to the characteristic that the polytropic exponent in the equation of the polytropic process of ideal gases remains the same, it is expounded that the specific heat of the polytropic process is closely related to the specific heat at constant volume of ideal gases. When the specific heat at constant volume of ideal gases is constant, all the thermodynamic processes with constant specific heat are classified as the polytropic processes of ideal gases, and there is no forbidden area for the value of the polytropic exponent. However, when the specific heat at constant volume of ideal gases varies with temperature, the thermodynamic processes with constant specific heat do not belong to polytropic processes, such as the adiabatic process with the zero specific being not a polytropic process, and there is a forbidden area for the value of the polytropic exponent. Only when the specific heat of a thermodynamic process resembles the specific heat at constant volume of ideal gases and has the same temperature dependency, can the thermodynamic process be a polytropic process of ideal gases. The basic characteristic of the polytropic process of ideal gases is that the difference between the specific heat of the process and the specific heat at constant volume is constant.

In this paper, the Nernst equation is applied to illustrate that when the temperature is equal to absolute zero, all the processes of a thermodynamic system are reversible and isothermal, overlapping with reversible adiabatic processes, and there is no zero-point heat. This solves the problem raised in textbooks and literature but not answered. For the thermodynamic system that does not satisfy the Nernst equation, further research is needed to determine whether there is zero-point heat.