entropy

dkamesh11,

I'll give you a simple answer, not the formal, complete answer you might get from a Willard Gibbs.

It is a measure of "useless" or "lost" energy that results from some process or change. It is generally thought of as spontaneous or proceeding without purpose.

Imagine a pot of hot water. It took energy to make the water hot and you can recapture some of that energy.

Now imagine a tray of ice cubes. It took energy to freeze that ice and you can recapture some of that energy.

Now put the ice cubes in the pot of water and wait. You now have warm water and you cannot recapture that energy that you could from the hot water and ice cubes.

This is entropy. It is sometimes called disorder.

The amount of entropy in the universe is thought to be increasing. Those folks who believe in the passage of time mostly think entropy is what tells us which direction time flows in.

Tom

Entropy is a really iritating concept...it's just the natural way everything wears out breaks down returns to chaos...ashes to ashes...it's such a depressing concept..it's about as much fun as thermodynamics...which is about as much fun as taking a cold shower and analysing why it is unpleasant.

I was cheerful before I started on this....

Del

Hi Del,

So, in other words, when my body temperature and the cold water coming from the showerhead are the same temperature, entropy is at maximum. It thus becomes unpleasant without any further analysis.

-John

Erratum to #3:

Probably not a good analogy since it's not an isolated system. Presumably, the water coming from the showerhead is unlimited, so the two elements; my body and the water, don't really reach an isolated equilibrium state. Here, equilibrium IS the temperature of the water! Still dang cold though.

So what really happened to entropy here?

One thing entropy isn't................enthalpy!!!!!

...........and don't spend too much time under the shower, we have drought conditions in most of Australia. Put all that water in a bucket and send it over here.....Is that Entropy???? I don't really care just send it over.

Which is about as much fun as sifting through your cat box, looking for what happened to your Tender Vitals!!!

Entropy is not energy and it is not a measure of uselessness, as some have pointed out. Entropy is a measure of disorder and in some analogous cases, uncertainty. There is a famous quote that sums it up "If you put a drop of wine in a barrel of sewer, you have a barrel of sewer. If you put a drop of sewer in a barrel of wine, you get a barrel of sewer" That is entropy at work.

Guest,

You correctly point out that I used sloppy language when I described entropy as a measure of "useless" energy; it would have been more correct to say that it is a measure of energy that is unavailable to do work. Your reply also points out very well that there are several points of view about entropy and, I think, there is no general reconciliation yet among the various POVs. Thank you for correcting me.

However, I raise an objection to your quote. If you put a drop of sewer in a barrel of wine, you get a barrel of wine. The cleansing properties of 3% alcohol are well known and historically documented.

Tom

I agree with your position Tom, but would YOU drink the wine?

I think I would. It can't be any worse than chittlins and I've eaten those.

Tom

Good one Sherlock, some wine does taste like shit!

Only some??? Ithought it was all wine.

Entropy is simply the name given to the decay process of all built-up systems, if exposed to the disordering nature of the universe, back to the pre-built system/s- this applies universally, as far as I know. Why?- the answer must be inshrined into the laws that created the universe- and exist in the on-going evolution(or decay) of built-up systems- although living creatures ingest energy to delay the inevitable. If we can answer the question of what is the basic, indivisible unit of all life, & does it exist irrespective of man,s, or even so- called lower forms, even insects, attempts at creating a built-up system, which serves for a while, until the entropy takes over- oh God, my brain(or whats left of it, is hurting- scuse me- glug, gluggity, glug- Burp!). Now what was I shaying?.

Everything stops.

For Tea ? (Noel Coward?)

Entropy is also an indication of the reversibility of physical processes. A process is reversible when it is possible to bring back both system and surrounding environment to the original thermo‑dynamic conditions.

For example, suppose to have a volume of air enclosed inside a cylinder with a movable piston. At the beginning the system is in thermo-dynamic equilibrium with the environment. Now, if you slowly compress the air with the piston, and the system may be assumed as "ideal" (i.e. adiabatic walls, no friction, no losses of any kind, etc.), the temperature of the air increases as the volume is decreased, but the "energy" of the system is unchanged: mechanical energy is turned in enthalpy. Then, once the piston is released, it is pushed backward, and the original condition can be restored in a – more or less – long time, necessary to re-establish the equilibrium conditions. The resulting entropy variation is zero.

If the cylinder is not adiabatic, part of the mechanical energy provided to the system will be dissipated to environment as heating power, during compression phase. The piston will not reach therefore the original position, and a different equilibrium status from original condition will be accomplished. The variation of entropy is just given by the heat transferred to environment.

P.S.: I'm boring by myself with this explanation, I apologize for that ….. probably the example of the packet of cigarettes or the can of worms would have been easier to explain

Imagine a container with a shutter inside... The shutter separates the space inside the container in 2 parts: left half & right half... There are 10 molecules of a gas at the left half ( the molecules are in motion=Brown's motion)... This is a condition of low entropy... You open the shutter and very soon the molecules are spreaded all over the space of the container... This is a condition of high entropy... Systems are directed from "low entropy" to "high entropy"... This is the so called "the arrow of the entropy"... (In the macroscopic systems this leads to the loss of energy as useless heat and, maybe, to the "time flow" or the "arrow of the time" as a related result...)

Of course, there is a possibility that there will be a moment, after a long time, that the 10 molecules will be gathered in the left half again... Then we could close the shutter and so the system will be in its initial condition... This possibility gives someone the sense that entropy is something deceptive... It's a statistic issue... The all you have to do is to wait (for as long as it's needed) and the system, eventually, will come again in a previous condition of low entropy...

Although this is possible for the simple system of 10 molecules, as the number of the mollecules is increased such a possibility is decreased dramatically... For a macroscopic systems which contains thousands or millions of mollecules such a possibility tends to be zero... That's why, in a macroscopic system, the entropy allways increased (as the opposite is extremelly unlikely, which means impossible)... With the same point of view, the whole Universe (as a huge system) always tends to increase its entropy... Of course, this happens in a general view (on the average) because the gravity, occasionally, plays its game and creates order (such as stars, galaxies and humans) from the general dissorder...

Hi George,

Would you consider this to be a form a reverse entropy?

(tongue-in cheek question, but nevertheless it's an interesting link).

-John

Hi John... I can't get in this link... I don't have access from my PC at work (and no PC at home)... It seems that I miss sth interesting...

Here's the thing I could never get about entropy and its Holy Edict...

"One man's chaos is another man's order!!!" It just seems like it all depends on your perspective.

Hi vermin,

What did you think about the link; reverse laminar flow?

Sorry, Johnjohn, but with a 56kbps modem It's really hard to view videos! I will look at it at work tomorrow. There, I have 10Gig to the desktop.

I do know that some fluids are capable of reestablishing order. Further, have you heard of "phase conjugate mirrors? You can send an image through bathroom glass and get the image back without any distortion from the glass in between. sort of an optical version of reversing entropy.

entrophy is frequently descriped as a measure of "Unavailablity of energy"

example: If you eat some calories.

You can't do or deliver the work to the equvalent to the energy you consumed

The reason is your body uses some qty of energy, due to the difference in the body temp and enviornment. To balance that diff it uses some qty of the enrgy from your intake or the source.

so that energy is not availble for delivering into work and become waste or un available or useless etc , etc, etc,.

there are many examples and several type if waste energy Which is added into atmosphere in one or the other form and become an enviorntmentally serious issue over a period of time

If you burn piece of wood it does not deliver the entire energy, it was possessing.... into heat. Still some ashes are left over and, that too have some energy value. some may use it (or) leave it as waste, useless and adding to the enviornemnt

This happens in any process / why in almost all the process

So the entophy is the energy discarded / unavailable for use/ considered as waste or useless / dumped into atomosphere ..........in several forms

Hope that this answer have reached your mind

sivabala

You have good wine or bad wine you are definitely going to add some entrophy to this atmophere.

I think you are forgetting the concept of flogistan!!! When you eat, surely the excess energy is taken up by balancing the bodily vapors! If not, then a good bleeding is in order to balance the system.

I will await your reply, while you powder your wig and rouge your lips - a must for any scientific discourse!!!

I love Flogistan! What a shame science has to move on...

It is the measure of disoderness of the system the higher the disoderness the higher the entropy. You can take it as an example from daily life of house or office where every thing is in proper sequence and you find the things with no efforts u can say the entropy of the house or office is extremly low .

so i hope u will find it helpful to understand entropy.