StatusX said:
A thermodynamical potential is a measurable quantity that represents the amount of energy that can be extracted from a thermodynamic system. It is used to describe the state of a system and determine its equilibrium conditions.
Some quantities are not considered thermodynamical potentials because they do not represent the amount of energy that can be extracted from a system. These quantities may not be directly related to the state of the system or may not be extensive, meaning their value depends on the size of the system.
Entropy is an example of a quantity that is not a thermodynamical potential. While it is a fundamental concept in thermodynamics, it does not represent the amount of energy that can be extracted from a system and is not an extensive property.
A quantity is considered a thermodynamical potential if it is an extensive property and its value depends only on the state of the system, not on its history. Additionally, it must be a unique function of the state variables of the system.
No, a quantity cannot be both a thermodynamical potential and not a thermodynamical potential. It must meet all the criteria of a thermodynamical potential to be considered as such. If a quantity does not meet these criteria, it is not considered a thermodynamical potential.