ABSTRACT
There exists a thermodynamic relation which, in certain conditions, links the changes of internal energy, entropy and volume during a process. It is useful because, among several calculations, it permits the determination of entropy change in a simplified way. Firstly, a transformation “identical” to that studied must be conceived. (By “identical”, it is signified that both transformations must have identical initial and final states). The important point is that the conceived identical transformation must be reversible. Along the course of this one, it is then possible to calculate the received entropy. In this case, it remains possible to imagine a reversible pathway, but it is necessary to involve a quasi-static process along this pathway. Entropy being a function of state, we can express its total differential as being a function of its differential partial coefficients. The reasoning is the same as in the cases of the internal energy and of the enthalpy.
