# Questions tagged [reversibility]

The potential for a thermodynamic process to be reversed in time. Alternatively, a quantification of how far an irreversible process is from being reversible, which relies on a comparison to a corresponding theoretical reversible process.

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### In order to explain a reversible change in thermodynamics, why is the following description irreversible?

I have a book that explains reversible processes as follows: A reversible change in thermodynamics is a change that can be reversed by an infinitesimal modification of a variable. [...] Suppose a gas ...
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### Why does a null entropy variation along a closed timelike curve imply a reversible process?

Carlo Rovelli in one of his articles from 2019 (reference: https://arxiv.org/abs/1912.04702) argues that time travel into the past are thermodynamically impossible: For instance, if we want to travel ...
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### What is the type of system, if I have an opened container with hot water inside, but no heat input to the system?

I have a school project, where I am trying to generate electricity using TEG modules that are attached to an aluminium container that contains hot water. The container is opened and there is no heat ...
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### How to find a complete understanding the 2nd law of Thermodynamics in terms of forms?

I have two straightforward question, and below I introduce more context to interpret them: What is, or is there, an order relation for forms that one can use to make sense of the 2nd law of ...
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### Confusion with Gibb's energy [duplicate]

For a reversible process , I can show that $$\mathrm dG=0$$ For the same reversible process I can also prove that $$\mathrm dG=\mathrm dW_{\text{max, non } P-V\text{ work}}$$ Does that imply maximum ...
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### What's the variation of entropy of an irreversible process?

I'm studying entropy, in particular the increase of entropy principle, and I have a doubt about the entropy variation of an irreversible transformation. If I have two thermodynamic states, A and B, ...
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### Quantum and classical physics are reversible, yet quantum gates have to be reversible, whereas classical gates need not. Why?

I've read in many books and articles that because Schrödinger's equation is reversible, quantum gates have to be reversible. OK. But, classical physics is reversible, yet classical gates in classical ...
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### How is entropy a state variable, and how can we measure entropy from irreversible processes with reversible ones, from a Khan Academy video

My questions : How is entropy a state variable? Why can we use a reversible process to measure an irreversible process's change in entropy if irreversible processes generate extra (unaccounted for ...
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### How can a quasi-static process be reversible?

As I understand it, a reversible process is required to be quasi-static because each infinitesimal step in a quasi-static process generates only infinitesimal amounts of entropy at a time which can be ...
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### Time's Arrow and QM

Something puzzles me. It is sometimes said that the fundamental equations of physics are time-reversible, creating the problem of time's arrow. But... isn't Schrodinger's wave equation time-dependent? ...
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### Doubt in the spontaneous process definition

Using the following definition I don't understand why a reversible process is not spontaneous. For an isolated system, a reversible process happen without any outside intervention. reversible process: ...
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