# Quasi-Static Process

## Main Question or Discussion Point

Just out of curiosity, is there any quasi-static process that is completely reversible? I think the answer is an obvious no because any quasi-static process experiences a net energy loss but I'd like to know if there are any, possibly something abstract rather then mechanical.

## Answers and Replies

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Andrew Mason
Homework Helper
Just out of curiosity, is there any quasi-static process that is completely reversible? I think the answer is an obvious no because any quasi-static process experiences a net energy loss but I'd like to know if there are any, possibly something abstract rather then mechanical.
Quasi-static processes ARE usually reversible. A reversible change is one in which the system and its surroundings are arbitrarily close to being in thermal equilibrium at all times. A quasi-static change is one that takes an arbitrarily long time to complete. Both are ideal situations and are not really achievable in practice.

AM

Andrew Mason
Homework Helper
Just as a follow-up. A quasi-static process that is not reversible would be one which takes an infinitely long time to complete but during which the system and surroundings are not infinitessimally close to equilibrium.

An example of a reversible process would be heat flow from an infinitely large reservoir at temperature T + dT to a system gas at temperature T. Heat would flow from the reservoir to the gas reversibly (ie system and surroundings are arbitrarily close to equilibrium at all times) and the gas at pressure P + dP would expand and do work at an infinitessimally slow pace (ie. quasi-static) against an external pressure P.

Now if, instead of doing work on its surroundings by expanding arbitrarily slowly against an external pressure of P, the gas simply escaped at an arbitrarily slow rate into a vacuum through a hole in the system container that was infinitessimally small, the process would be quasi-static (ie it would take an infinite or arbitrarily long time) but would not be reversible (you could not with an arbitrarily small change in conditions get the gas to flow back from the vacuum into the system container).

AM

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