# Entropy for reversible and irreversible cycles.

• corona7w
In summary, entropy can be thought of as a measure of how reversable the system is. 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.

#### corona7w

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?

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)

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

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

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

## 1. What is entropy in reversible and irreversible cycles?

Entropy is a thermodynamic property that measures the degree of disorder or randomness in a system. In reversible cycles, entropy remains constant as the cycle is reversible, while in irreversible cycles, entropy increases due to the presence of irreversibilities.

## 2. How is entropy related to heat transfer in reversible and irreversible cycles?

In reversible cycles, the change in entropy is directly proportional to the heat transfer, as the process is reversible and the heat transfer is a reversible process. In irreversible cycles, the change in entropy is greater than the heat transfer, as some of the heat is lost to the surroundings due to irreversibilities.

## 3. Can entropy be decreased in a reversible cycle?

No, entropy can only remain constant or increase in a reversible cycle. This is because reversible processes have no irreversibilities and therefore no increase in entropy.

## 4. What is the difference between entropy generation and entropy increase in irreversible cycles?

Entropy generation refers to the increase in entropy due to irreversibilities in a process. Entropy increase, on the other hand, refers to the overall increase in entropy including both reversible and irreversible processes.

## 5. How does entropy relate to the efficiency of a reversible cycle?

In a reversible cycle, the efficiency is equal to the ratio of the heat transfer to the maximum possible heat transfer. This maximum possible heat transfer is given by the change in entropy of the system. Therefore, entropy plays a crucial role in determining the efficiency of a reversible cycle.