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### Topic: Negative entropy.  (Read 68948 times)

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#### Jose M.

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##### Negative entropy.
« on: September 03, 2006, 03:55:46 PM »
Hi. Thermodynamics is the study of energetic processes in physical and chemical processes.

First Law. Energy can be transfered and transformed, but cant be created nor destroyed. The energy of the Universe is constant and conserved.

Second Law. In every natural process, thermal energy (heat) is produced. Heat is the most random and disordered form of energy, the random kinetic movement of particles. Therefore, with this heat production, the entropy (S) (disorder) of the Universe is constantly increasing.

Third Law. An ideal (perfect) crystal solid at 0 degrees Kelvin has 0 entropy. Must be Kelvin, because it is an absolute 0. In Kelvin there is no such thing as temperatures below 0.

Entropy (S) is randomness and disorder. The concept entropy was introduced and described by Clausius.

Now, my question. I have heard of something very strange, a concept difficult to grasp and assimilate: negative entropy. In mathematics, negative numbers make plenty of sense to me: a negative number is a loss, deficiency or debt. However, I find it difficult to see physical meaning in negative entropy. An ideal crystal solid at 0 degrees Kelvin cant possibly be any more ordered, so how can there be negative entropy ? Please explain to me the negative entropy concept. It will be appreciated. Thanx.

#### Yggdrasil

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##### Re: Negative entropy.
« Reply #1 on: September 03, 2006, 04:02:32 PM »
Entropy cannot be negative for the reason you give.  If 0 entropy refers to perfect order and S > 0 refers to less-than-perfect order, S < 0 would have to mean more-than-perfect order which makes no sense.

What can be negative is delta S, the change in entropy.  For example, in condensation, the transition from a gas (high entropy state) to a liquid (low entropy state), the change in entropy is negative, but both states have positive entropy.

#### Jose M.

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##### Re: Physical changes.
« Reply #2 on: September 03, 2006, 05:08:13 PM »

Now that you say it, I will say the following.

Gas to liquid: condensation.
Liquid to solid: freezing.
Solid to liquid: fusion.
Liquid to gas: evaporation.
Gas to solid: deposition.
Solid to gas: sublimation.

Yep, I know the names of the physical changes.

#### tamim83

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##### Re: Negative entropy.
« Reply #3 on: September 06, 2006, 12:36:15 PM »
There may be no "negative" entropy (as in absolute entropy), but you could have a negative "change in entropy", which would mean that the system becomes more ordered, which is completely valid.

I have seen entropy values reported as negative numbers for some ions in aqueous solution.  I think this is because solvation creates a more ordered system than a "free ion".  So perhaps the entropy change for solvation of the ion is what is being reported.

#### zeifer_roth

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##### Re: Negative entropy.
« Reply #4 on: October 01, 2006, 09:39:27 AM »
hi.. im a chemical engineering student...

entropy also is a measure whether a given process is possible or not...

* a delta s > 0 mean that the process is possible but irreverilble

* a delta s = 0 means that a process   is possible but reversible

* a delta s < o means that a process is impossible

therefore a negative entropy is impossible.. because youre process in the first place is impossible.. but these change in entropy means the total change in entropy

your total delta s = delta S (system) + delta S of your sorrounding

on a certain process a negative entropy can be attain by one part of the total delta S

a negative entropy can be attain by a system only or the sorrounding only but for a possible process your if your system has a negative entropy the sorrounding has possitive entropy which may be greater or equal in magnitude with the system entropy.. but your total entropy is still ( delta S >= 0)

yippee luks like im listemimg to my teacher in thermodynamics hehehe

#### edwinksl

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##### Re: Negative entropy.
« Reply #5 on: October 04, 2006, 09:47:05 AM »
ya i guess you are right, at least from what little thermodynamics knowledge i have