# Thermodynamics and was looking at the second law

1. Nov 6, 2004

### misogynisticfeminist

I'm new to thermodynamics and was looking at the second law. From what I know, the 2nd law is constantly violated locally (in a non-isolated system), but this violation locally causes an increase in entropy in an isolated system. Am I right here??? or is my understanding flawed? if its not, then are there any examples of this?

2. Nov 6, 2004

### somy

the second law is dealing with both system and its envirinment.
you can not tell anything by ignoring one of them. ok???

3. Nov 6, 2004

### dextercioby

The second law states that entropy increases in isolated systems (as it can be shown using Boltzmann's kinetic equation).The only isolated system physicsist know is the entire Universe,so applying the second law,in the entire Universe the entropy increases with time (and viceversa,though i don't know anybody having proven the fact that time flow is inextricably linked to entropy increase (maybe smb proved that,but i haven't read about it,but I'd like to)).
To say that
is virtually wrong because the second law doesn't tell what happens to the entropy in non-isolated systems.It could be constant,increase,decrease,depends on the interactions between the studied system and the environment.

I've allways considered this (Rudolf Clausius 1865(?)) formulation of the second law as the most important achivement in physics in the XIX-th century,alongside Faraday's 1831 discovery of electromagnetic induction.

4. Nov 6, 2004

### misogynisticfeminist

^ hmmmm, understood, so can it be safe to say that the second law does not apply to non-isolated systems ??

5. Nov 6, 2004

### dextercioby

It does,but in other formulations.Clausius's formulation refers only to isolated systems and i guess it's the only one of them to do so.
The thermodynamics teacher told us that classical equilibrium thermodynamics has two formulations.The empirical one,and the axiomatical/theoretical one (due mostly to Gibbs,hence "neogibbsian" formulation of classical equilibrium thermodynamics).The former has a long history,and has numerous formulations for its principles (as I recall,they're 5 of them (i.e. principles)),and especially for the second principle.The latter is based upon the definition and the properties of the thermodynamical function called ENTROPY.It's formulation of the second principle includes Clausius formulation for the second principle in the so-called "CTPCN" (apud Clausius-Thomson-Carathéodory-Planck-Nernst) formulation (which is the name for the first formulation stated above) and it's essential to be taught for its beautiful derivation from classical &/V quantum equilibrium statistical mechanics.

6. Nov 6, 2004

### Clausius2

Thanks for quoting me. Yes, in fact in those years we were a nice group of guys trying to figure out what the hell was entropy.

7. Nov 8, 2004

### dextercioby

Dann Du muss ein Deutsche sein,nich wahr??

8. Nov 9, 2004

### Clausius2

Selbstverständlich obgleich ich normalerweise meinen Feiertag in Benidorm verbringe.

:rofl: :rofl: :rofl: