Entropy for reversible and irreversible cycles.

corona7w · Feb 22, 2009

I am confused about the entropy change for reversible and irreversible cycles. I know entropy is a state function, so for cycles, the entropy change within the system should be 0, since the process ends up in the same state as the beginning. So does this mean that the entropy change for the system is 0 for both reversible and irreversible cycles?

lanedance · Feb 23, 2009

look at this thread

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

xxChrisxx · Feb 23, 2009

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)

Andrew Mason · Feb 23, 2009

corona7w said: ↑

I am confused about the entropy change for reversible and irreversible cycles. I know entropy is a state function, so for cycles, the entropy change within the system should be 0, since the process ends up in the same state as the beginning. So does this mean that the entropy change for the system is 0 for both reversible and irreversible cycles?

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

lanedance · Feb 23, 2009

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

Andrew Mason · Feb 23, 2009

lanedance said: ↑

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

Log in or Sign up

Entropy for reversible and irreversible cycles.

corona7w

lanedance

xxChrisxx

Andrew Mason

lanedance

Andrew Mason

Entropy for irreversible process (Replies: 12)

Change in entropy in irreversible and reversible process (Replies: 9)

Entropy related questions - Reversible or Irreversible? (Replies: 2)

Entropy of isothermal process reversible\irreversible (Replies: 0)

Entropy of gas expansion, isothermal/reversible vs irreversible (Joule), ideal vs VDW (Replies: 6)