# Entropy => Energy?

AThousandYoung
Science 15 Mar '09 20:30
1. AThousandYoung
West Coast Rioter
15 Mar '09 20:30
Prove or disprove:

All events that result in an increase of entropy can theoretically be harnessed to produce usable energy.
2. 15 Mar '09 20:48
Define "usable".
3. 15 Mar '09 21:12
A possible answer to your question: if you consider some system in thermal equilibrium with its surroundings, the helmholz free energy is given by F = U - TS, an increase in entropy will reduce the helmholz free energy and therefore reduce the amount of work that can be done.
4. AThousandYoung
West Coast Rioter
16 Mar '09 02:11
Originally posted by KazetNagorra
Define "usable".
Gibbs free energy might fit the bill.
5. 16 Mar '09 09:44
Originally posted by AThousandYoung
Gibbs free energy might fit the bill.
Pretty much the same applies as for the post above, though it's a different equilibrium. The factor -TS is also in the Gibbs free energy, so it's reduced by an increase in entropy.
6. 20 Mar '09 19:21
If you look at entropy at a molecular level, it is basically the breaking of bonds between atoms to create simpler molecules. Every time you break a molecular bond, energy is liberated because there is a transfer of electrons.

I think this can prove that THEORETICALLY, every increase in entropy can be harnessed into useful energy.
7. 20 Mar '09 20:04
Originally posted by dannyUchiha
If you look at entropy at a molecular level, it is basically the breaking of bonds between atoms to create simpler molecules. Every time you break a molecular bond, energy is liberated because there is a transfer of electrons.

I think this can prove that THEORETICALLY, every increase in entropy can be harnessed into useful energy.
Actually entropy is simply proportional to the log of the number of states available to the system, which may or may not correspond to the number of bonds. A process in which entropy increases can be used for useful energy in some cases but not always, how are you going to get useful energy out of the melting of ice cubes in a glass of water?
8. AThousandYoung
West Coast Rioter
21 Mar '09 06:11
Originally posted by KazetNagorra
Actually entropy is simply proportional to the log of the number of states available to the system, which may or may not correspond to the number of bonds. A process in which entropy increases can be used for useful energy in some cases but not always, how are you going to get useful energy out of the melting of ice cubes in a glass of water?
That's right. Some increases in entropy require energy input. I guess you've disproven my hypothesis.
9. 21 Mar '09 16:31
Originally posted by KazetNagorra
Actually entropy is simply proportional to the log of the number of states available to the system, which may or may not correspond to the number of bonds. A process in which entropy increases can be used for useful energy in some cases but not always, how are you going to get useful energy out of the melting of ice cubes in a glass of water?
You're right. I was thinking of some processes that were useful, but clearly not all are. Thanks for clearing that up.
10. 23 Mar '09 08:59
Originally posted by dannyUchiha
If you look at entropy at a molecular level, it is basically the breaking of bonds between atoms to create simpler molecules. Every time you break a molecular bond, energy is liberated because there is a transfer of electrons.
That is not true at all. Entropy has no direct relationship to the number of chemical bonds or the complexity of molecules. If you were right then many chemical reactions would violate the second law.
11. 23 Mar '09 12:21
That is not true at all. Entropy has no direct relationship to the number of chemical bonds or the complexity of molecules. If you were right then many chemical reactions would violate the second law.
Of course it doesn't have a direct relationship with the number of bonds or with the complexity of the molecule. That's not what I said.

What I said was that it involved breaking of bonds. As you may know, entropy is the increase in disorder of a system. This may or may not liberate energy, but I do believe it involves some sort of interaction between atoms (breaking and/or formation of bonds)

Can you give examples when this does not apply?
12. 23 Mar '09 12:23
That is not true at all. Entropy has no direct relationship to the number of chemical bonds or the complexity of molecules. If you were right then many chemical reactions would violate the second law.
Also, you might want to reread the second law of thermodynamics.

http://en.wikipedia.org/wiki/Second_law_of_thermodynamics
13. DeepThought
23 Mar '09 15:37
Originally posted by dannyUchiha
What I said was that it involved breaking of bonds. As you may know, entropy is the increase in disorder of a system. This may or may not liberate energy, but I do believe it involves some sort of interaction between atoms (breaking and/or formation of bonds)

Can you give examples when this does not apply?
Entropy, as KazetNagorra stated above, is the log of the number of available states. It is fairly easy to show that it is a non-decreasing function of time. The breaking of molecular bonds is not necessary for an increase in entropy.

Here is an example: Imagine helium in a thermally isolated cylinder. First you compress the gas very slowly the volume drops and the pressure and temperature increase, you can then slowly reverse the process and the gas will end up in the state it started in. Now instead of compressing it slowly compress it quickly. This will cause an irreversible change. When you try to restore the gas to its earlier state you will find that the pressure and temperature are different to the initial state. Helium is a noble gas and will not form molecules.
14. 23 Mar '09 17:051 edit
Originally posted by dannyUchiha
Of course it doesn't have a direct relationship with the number of bonds or with the complexity of the molecule. That's not what I said.

What I said was that it involved breaking of bonds. As you may know, entropy is the increase in disorder of a system. This may or may not liberate energy, but I do believe it involves some sort of interaction between ...[text shortened]... atoms (breaking and/or formation of bonds)

Can you give examples when this does not apply?
It's a bit inaccurate to view entopy as a measure of disorder. Although it usually comes down to this, you must remember that disorder on a microscopic scale can result in ordering on a macroscopic scale. For example, the demixing of a fatty liquid in water results in an increase in entropy (also note that no chemical bonds are involved in this process).
15. 24 Mar '09 13:06
Originally posted by dannyUchiha
Also, you might want to reread the second law of thermodynamics.

http://en.wikipedia.org/wiki/Second_law_of_thermodynamics
I have gone and read it and I see nothing that contradicts what I said.
Put Hydrogen and Oxygen in a box in an isolated part of space and light it with a spark. Over time it will burn to form water. This either contradicts what you were saying or contradicts the second law.