The Reversible Thermodynamic Processes and its Place in Physics
Reversible processes do exist in nature. Light in a vacuum is a reversible process. It produces no entropy. It is perpetual until it is disturbed/absorbed. Because it is a process, it has more than one state: [Its displacement current creates light's magnetic vector which in turn creates the electrical vector, which creates the magnetic vector...] , it produces a work product: [the transport of electromagnetic energy in space/time].
The covalent bond is another. It produces no entropy. It too is perpetual untill disturbed. It has two states: the energy association with one then the other atom. It produces a work product: the union of two atoms.
I want you to know that the reversible process only exists in wave mechanics, and cannot have any mass particles within the process. Mass always has Heisenberg Uncertainty...which is entropy...and it is not permitted in a reversible process. I also want you to note that the covalent bond involves mass particles...IN ITS WORK PRODUCT...not in the process itself which consists of energy that is associated with one and then the other atom. This is an important distinction between the reversible process itself and its work product.
You can certainly ask me to describe the other two that I know of...or you can look at my lecture on the subject:
https://www.youtube.com/watch?v=YvR0gYL_Tq0&t=48s
https://www.youtube.com/watch?v=_ORtIUbDZzQ&t=4s
Ask me a question. I am an independent scholar with 45 years of independent scholarship on this subject.