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This doesn't make sense to me because why not extend the state space to include the changed factor? Because the hysteresis is defined relative to set of variables that are directly controllable b …

But when I take it through an adiabatic reversible process to the same state as I did in the irreversible process, You assume this is possible, but nobody has succeeded doing so. If someone did, …

There are several different concepts of reversibility. … In the context of the 2nd law of thermodynamics the important one is thermodynamic reversibility, which means one can return from the final state of the system+environment to the original state, getting …

But in the case of irreversible paths there is no corresponding curve along which we can integrate, therefore what does $\oint \frac{dQ_{irr.}}{T}<0$ even mean? The Clausius inequality you ask a …

Great, similar questions have been bothering me too for quite some time. Arnold, I do not understand your post. The question is about the Fermi golden rule, but I did not see any mention of imaginary …

If you know the equilibrium states $a,b$, entropy change when going from $a$ to $b$ is definite and does not depend on details of the process, or whether it is reversible or not. A reversible process …

Spontaneous macroscopic heat flow is always irreversible as it involves difference of temperatures. However, the lower the difference of temperature, the closer the process is to being reversible. In …

You are right that in general, system's state is so non-equilibrium that it has no thermodynamic state variables, so $pV$ diagram or similar representation of the cycle cannot be drawn. For example, f …

Reif perhaps means that in a reversible process, entropy of the supersystem (the system + the reservoir that exchanges heat with it) remains constant. Together with Boltzmann's/Planck's observation th …

Although I think I understand the basic definition, I don't see why we need the concept of a quasistatic process? Which equations or concepts in thermodynamics actually rely on this kind of process …

why is it not true also that the work done is for non-reversible processes as well? The general expression for infinitesimal work done by contact pressure forces on a system inside a closed bound …

If all these statements are true, then isn't it true that all reversible engines operate at Carnot efficiency? It is true provided the reversible engines operate between the same pair of tempera …

When textbooks write $dS=dQ/T$, quasi-static process with no friction is considered. $S$ is entropy of the system, $dQ$ is heat accepted by the system from the environment and $T$ is temperature of th …

1) Entropy is supposed to be a state function so shouldn't any loop on the PV plane bring the system to its initial state and thus its initial entropy? Pair of values $P,V$ may not be enough to s …

A process is something that goes on, has duration. A change has no necessary relation to time. It is a statement of difference between the initial and the final state of the process.