Is a quasi-static but irreversible process possible?

• I
Hello.

I read the textbook of the thermodynamic and it said the definition of the reversible process as "thermodynamic process which is slow enough so the system state is always infinitesimally close to the thermodynamic equilibrium (quasi-static) during the process. Such a process can always be reversed without changing the thermodynamic state of the universe". I accepted this definition in a way that "quasi-static" and "reversible" is equivalent.

Is this true? Is there any process which is quasi-static but not reversible?

Chestermiller
Mentor
Heat transfer from a hot slab to a cold slab through an intervening wall of very low thermal conductivity.

Last edited:
goodphy
Mapes
Homework Helper
Gold Member
Is there any process which is quasi-static but not reversible?

A reversible process doesn't increase entropy and thus cannot exist in the real world (although we can come arbitrarily close). Every real process is irreversible. You can generally slow down a process as much as you wish to satisfy your criterion for "quasi-static". Another simple example to complement Chester's is a container of water with a pinhole opening, left to evaporate. Others are a battery attached to a very high resistance, a load applied to a solid at a low temperature (i.e., a solid with little propensity to creep) or a high-viscosity liquid, a nonspherical asteroid, or an amorphous solid whose equilibrium state is crystalline.

Castello and goodphy
A reversible process doesn't increase entropy and thus cannot exist in the real world (although we can come arbitrarily close). Every real process is irreversible. You can generally slow down a process as much as you wish to satisfy your criterion for "quasi-static". Another simple example to complement Chester's is a container of water with a pinhole opening, left to evaporate. Others are a battery attached to a very high resistance, a load applied to a solid at a low temperature (i.e., a solid with little propensity to creep) or a high-viscosity liquid, a nonspherical asteroid, or an amorphous solid whose equilibrium state is crystalline.

Thanks you! you and Chestermiller suggest examples of a quasi-static and irreversible process. I've searched the internet and found that the reversible process is quasi-static but its converse is not guaranteed. So, I think the definition of the reversible process given in my book has some hole. So, the true definition of the reversible process is that the reversible process is the process which doesn't change a total entropy of the system and its surrounding or simply the entropy of the universe, right?

Could you tell me why the reversible process has to be quasi-static? Why the process which is done pretty much fast so never be quasi-static has to be an irreversible process?

Mapes