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

1. Sep 24, 2010

### 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!

2. Sep 24, 2010

### Andrew Mason

Re: No change in entropy of the system+surroundings in "reversible" process.Really?

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

AM

3. Sep 25, 2010

### kntsy

Re: No change in entropy of the system+surroundings in "reversible" process.Really?

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