Homework Help: Entropy for reversible and irreversible cycles.

look at this thread

https://www.physicsforums.com/showthread.php?t=203797

 

Entropy can be thought of as a measure of how reversable the system is. So an ideal system would be reversable and has an entropy change of 0.

Irreversable cycles lose something to the surroundings, so you can take the ideal cycle and apply real world components to it. Those components will never be 100% efficient meaning you cannot travel back along the line (reverse the process) and get that energy back from the surroundings.

Entropy has to be one of the most mind bending concepts to grasp at first (sometimes I still get confised)

 

Yes. The change in entropy of a system is the integral of dQ/T on a reversible path between two states. If there is no change in the state of the system, there can be no change in entropy. The difference between reversible and irreversible processes is in the entropy change of the surroundings.

AM

 

but Andrew wouldn't you say the entropy of an isolated system can increase without interacting with its surroundings... (basically 2nd law of thermo)

 

Of course. But it will necessarily end up in a different state.

AM