a common example for irreversible process given is the rapid expansion of a piston due to sudden reduction in external pressure(as against very slow reduction in a reversible case). In this case, it is stated that maximum useful work derived is less, because piston does less useful work (as illustrated via area under the curve in P-V work).But this is mathematical explanation more or less. What I am trying to understand is intuitively, why does this happen? why is work done less? where does the "non-useful " work end up as? assume it is a frictionless system. Describe at a microscopic level, keeping it less mathematical.
My guess: the molecules of gas within piston chamber end up doing compression-expansion work of some sort on themselves which doesn't show up as useful work. But I am not able to visualize this. also in this example has the entropy of system increased as well as surroundings? or only system? or both?