Let us look at this situation.
Consider a container having a gas trapped inside, facing pressure from masses M1 and M2, assume that this system is at equilibrium. Here point A represents the initial position of the piston before mass M2 is removed.
After removing mass M2 the pressure decreases and the volume of the gas increases forcing the piston to rise up. Here point B represents the final position of the piston after the system has attained equilibrium again.
"The aforementioned situation is an irreversible process." , said my teacher.
My question is -
Why and how will the parameters(state functions) change from their initial values while going back from B to A resulting in the journey from A to B to become irreversible?