Query on Isentropic relationships (such as PV^gamma = constant)

[randomuser1]

Hi all, I have a question. So from the derivation of the Isentropic process relationship PV^gamma = constant, there is a step dW = PdV, which can only be said for quasi-equilibrium (or reversible) processes. As such I believe PV^gamma = constant (and the family of equations) should not be applicable to just adiabatic processes? Ie, it should be applicable only for adiabatic + reversible = isentropic processes?

However, I've seen couple of online notes/books, and http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/adiab.html#c3 case in point, using PV^gamma = constant for adiabatic process. My suspicion in that in these sources, when they say adiabatic, they really mean isentropic?

Thanks. Also, not sure if this is the right area to post this but yea...

 

[boneh3ad]

You are correct, it does not apply to adiabatic, irreversible processes. But that's kind built right into the word itself: isentropic. That implies the process must be constant-entropy, i.e., reversible.

I don't immediately know why the site you link is using it without specifying the reversibility condition.