# Reversible and Quasi-static processes

Do we have any proof that reversible processes are always quasi-static or is it just a fact that hasn't been violated till date? If there is a proof then please provide a link.

This comes from just definations.

In thermodynamics, a quasi-static process is a thermodynamic process that happens infinitely slowly.

Reversible process:Any process which can be made to proceed in the reverse direction by variation in its conditions such that any change occurring in any part of direct process is exactly reversed in the corresponding part of reverse process is called reversible process.

Conditions for Reversibility :

1.The substance undergoing a reversible change must at all instances be in thermodynamic equilibrium with its surroundings. It means the pressure and temperatures of the working substance must never differ appreciably from its surroundings at any stage of the cycle of operation.

2.All the processes taking place in the cycle of operation must be infinitely slow.

3.There should be complete absence of frictional forces.

4.There should not be any loss of energy due to conduction, convection or radiation during the cycle of operation.

Now why a reversible process need to be quasi-static?

Ans:The process must be carried out infintesimally slowly so that the system remains in the thermal and mechanical equilibrium with sorroundings throughout. further information: http://www.gitam.edu/eresource/Engg_Phys/semester_1/THERMODYNAMICS/rev_and_irrev.htm

• But again is the condition of quasistatics a necessary one for the process to be a reversible one? My question is looking for specific proofs for the need of quasistatics for reversibility and if there are no proofs then is it that every reversible process discovered or thought of till date ends up being quasistatic i.e. there is no violation till date. Jan 20, 2015 at 18:40
• In quasi-static processes there can be friction but in reversible processes not.
– Paul
Jan 20, 2015 at 18:44
• To rephrase the comment of @Paul: If there is friction the process needs to be quasi-static to be reversible, whereas if there is no friction it might not need to be quasi-static to be reversible (e.g.: a friction-less pendulum). However, I think "quasi-static" Nov 15, 2020 at 9:05