# No change in entropy of the system+surroundings in reversible process.Really?

• kntsy
In summary, reversible processes must not only be reversible, but also isothermal or adiabatic in order for the total change in entropy of the system and surroundings to be zero. This can be seen through the equation \triangle S_{total}=\triangle S_{in} +\triangle S_{out}=0, which is only true for reversible isothermal or adiabatic processes.
kntsy
No change in entropy of the system+surroundings in "reversible" process.Really?

This is a challenge to the sentense from some basic text.
I think reversible is not enough.
It has to be ISOTHERMAL, right?
Lets me be sure that i am correct!

kntsy said:
This is a challenge to the sentense from some basic text.
I think reversible is not enough.
It has to be ISOTHERMAL, right?
Lets me be sure that i am correct!
No. An adiabatic process (eg. expansion or compression) can be reversible. In such a case, the temperature is not constant.

AM

Andrew Mason said:
No. An adiabatic process (eg. expansion or compression) can be reversible. In such a case, the temperature is not constant.

AM

Thanks! But what about REVERSIBLE isobaric, isovolume,? The total system+environment change in entropy still can remain zero?
I discover an important fact:
$$\triangle S_{total}=\triangle S_{in} +\triangle S_{out}=0$$
iff
$$\int\frac{dq_{in}}{T}=\int\frac{dq_{out}}{T}$$
iff

Last edited:

## 1. What is entropy and how does it relate to reversible processes?

Entropy is a measure of the disorder or randomness in a system. In a reversible process, the entropy of the system and its surroundings remains constant, meaning there is no net change in the overall disorder of the system. This is due to the fact that reversible processes are considered to be ideal and have no loss of energy or increase in disorder.

## 2. How do you determine if a process is reversible or irreversible?

A reversible process is one that can be reversed by an infinitesimal change in the system or its surroundings. This means that the system and surroundings can be returned to their original state without any loss of energy or increase in disorder. In contrast, an irreversible process results in a net loss of energy or increase in disorder and cannot be reversed without external influence.

## 3. Can irreversible processes occur in nature?

Yes, irreversible processes can occur in nature. In fact, most processes that occur in the real world are irreversible to some extent. This is due to the fact that there is always some energy loss or increase in disorder during a process, even if it is small. However, reversible processes are often used as ideal models to understand and analyze real-world processes.

## 4. What is the significance of no change in entropy in a reversible process?

A reversible process with no change in entropy is considered to be an ideal process that is perfectly efficient. This means that all of the energy put into the process is converted into useful work, without any loss. This concept is important in thermodynamics and is used to define the concept of a perfect or idealized system.

## 5. Can the entropy of a system and its surroundings ever decrease?

No, the second law of thermodynamics states that the total entropy of a closed system, including its surroundings, can never decrease over time. This means that in a reversible process, the entropy of the system and its surroundings remains constant, while in an irreversible process, the total entropy will always increase.

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