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Suppose i have a bucket full of water in a closed room,the water is

by nouveau_riche
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Drakkith
#37
Jul26-11, 04:54 PM
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Quote Quote by nouveau_riche View Post
the entropy of water molecule in air is more than in water
While this is true in your example and similar situations, I am unsure whether that is true in ALL situations.
nouveau_riche
#38
Jul27-11, 02:53 AM
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Quote Quote by Drakkith View Post
While this is true in your example and similar situations, I am unsure whether that is true in ALL situations.
u need to find one then,i myself will look for the same
but as this goes true in mine example i still am looking for an answer from DALESPAM
nouveau_riche
#39
Jul27-11, 02:54 AM
P: 253
ANSWER TO THIS

well,thanks for this easy example,as seen in this example that the average K.E of molecules goes down both in air and water,but in this context the entropy of system as a whole cannot be connected to temperature,in a sense-"the place with high entropy will have more energy".
to my knowledge that is true but the example you have presented here is an exception?
hacillunation
#40
Jul27-11, 07:58 AM
P: 7
Hi,
A quick question from someone who don't know how entropy works-
Why do molecules in the air have more enthropy than those in the water?

I thought that "entropy" is the amount of energy that can do useful work.
Aren't the evaporated molecules in the second stage after doing their work.

Thank you very much.
nouveau_riche
#41
Jul27-11, 10:26 AM
P: 253
Quote Quote by hacillunation View Post
Hi,
A quick question from someone who don't know how entropy works-
Why do molecules in the air have more enthropy than those in the water?

I thought that "entropy" is the amount of energy that can do useful work.
Aren't the evaporated molecules in the second stage after doing their work.

Thank you very much.
the entropy describes disorder,the molecule in water have high molecular interaction than in air,therefore the molecule will create a more disorder state in air
nouveau_riche
#42
Jul27-11, 10:32 AM
P: 253
Quote Quote by Drakkith View Post
While this is true in your example and similar situations, I am unsure whether that is true in ALL situations.
i think i have a situation where my assertion could get false
"consider a box containing 4 molecules all with K.E of 40(in any unit),the molecules are bouncing back and forth between the opposite walls,now suppose there is another box that contains same number of molecules with K.E of 10 each but they deprive of the condition of being oscillatory(as in previous case) ,so they have a randomized nature, which will be perceived as a state of more disorder though it has less average K.E.
hacillunation
#43
Jul27-11, 11:53 AM
P: 7
Umm...ok I understand what you are saying...

But how does this coincide with: "Entropy is a thermodynamic property that can be used to determine the energy available for useful work in a thermodynamic process..." (Wiki)?

Thanks.
thebiggerbang
#44
Jul27-11, 02:31 PM
P: 70
Uh oh! The problem with OP is that he is constructing a hypothetical experiment that will clash with the time tested laws of thermodynamics. Assuming that OP talks about a closed system, let's sit and explain this once he obtains the results that he assumed above! :P
thebiggerbang
#45
Jul27-11, 02:35 PM
P: 70
Quote Quote by hacillunation View Post
Umm...ok I understand what you are saying...

But how does this coincide with: "Entropy is a thermodynamic property that can be used to determine the energy available for useful work in a thermodynamic process..." (Wiki)?

Thanks.
The Gibbs free energy equation states that
[itex]\Delta[/itex]G=[itex]\Delta[/itex]H-T[itex]\Delta[/itex]S

where [itex]\Delta[/itex]G is the useful energy available to do work
[itex]\Delta[/itex]H is the enthalpy change in the process
T equals the temperature in Kelvins
[itex]\Delta[/itex]S relates to the change in enthalpy.

Always remember that a negative value of [itex]\Delta[/itex]G gives us a spontaneous reaction!
hacillunation
#46
Jul27-11, 08:27 PM
P: 7
Not exactly what I asked but it helped me to figure out, :P

Another quick question- When gaseous particles move due to their heat/energy, their motion would be endless if they wouldn't collide with anything? If so, then wouldn't that mean that potential energy turned into work, meaning no entropy?


Thx.



PS. How do you say it, "collide in something" or "collide with something"?
DaleSpam
#47
Jul27-11, 09:28 PM
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Quote Quote by nouveau_riche View Post
the entropy of system as a whole cannot be connected to temperature,
It is "connected" to the temperature, but it is also a function of other things besides only temperature. That is why I poated the link to the hyperphysics page. Even if you don't fully understand everything about it you can at least see that it is a function of more than just temperature.

Quote Quote by nouveau_riche View Post
in a sense-"the place with high entropy will have more energy".
to my knowledge that is true but the example you have presented here is an exception?
That is true (except it is about changes in entropy and changes in energy, not absolute values of either). This situation is not an exception, energy goes from the low entropy liquid phase to the high entropy vapor phase. In fact, that is exactly what drives the whole process. It is not an exception, it is an example.
nouveau_riche
#48
Jul28-11, 06:27 AM
P: 253
Quote Quote by DaleSpam View Post
It is "connected" to the temperature, but it is also a function of other things besides only temperature. That is why I poated the link to the hyperphysics page. Even if you don't fully understand everything about it you can at least see that it is a function of more than just temperature.

That is true (except it is about changes in entropy and changes in energy, not absolute values of either). This situation is not an exception, energy goes from the low entropy liquid phase to the high entropy vapor phase. In fact, that is exactly what drives the whole process. It is not an exception, it is an example.
this is the exception

i think i have a situation where my assertion could get false
"consider a box containing 4 molecules all with K.E of 40(in any unit),the molecules are bouncing back and forth between the opposite walls,now suppose there is another box that contains same number of molecules with K.E of 10 each but they deprive of the condition of being oscillatory(as in previous case) ,so they have a randomized nature, which will be perceived as a state of more disorder though it has less average K.E.

Old Y, 11:53 AM
DaleSpam
#49
Jul28-11, 03:58 PM
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Quote Quote by nouveau_riche View Post
this is the exception

i think i have a situation where my assertion could get false
"consider a box containing 4 molecules all with K.E of 40(in any unit),the molecules are bouncing back and forth between the opposite walls,now suppose there is another box that contains same number of molecules with K.E of 10 each but they deprive of the condition of being oscillatory(as in previous case) ,so they have a randomized nature, which will be perceived as a state of more disorder though it has less average K.E.

Old Y, 11:53 AM
It sounds like you are describing sublimation, where something goes from a solid state with very constrained motion to a vapor state with free motion. It is, in principle, no different from the evaporation that we have been discussing. The energy goes from the low entropy solid state to the high entropy vapor state.
nouveau_riche
#50
Jul29-11, 07:51 AM
P: 253
Quote Quote by DaleSpam View Post
It sounds like you are describing sublimation, where something goes from a solid state with very constrained motion to a vapor state with free motion. It is, in principle, no different from the evaporation that we have been discussing. The energy goes from the low entropy solid state to the high entropy vapor state.
which box will have more entropy(in the exception i have given)?
DaleSpam
#51
Jul29-11, 11:04 AM
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There is not enough information given. The entropy of a gas depends on other things besides just the temperature (and I don't know how to calculate the entropy of a solid):
http://hyperphysics.phy-astr.gsu.edu...entropgas.html

However, given the right conditions for the other variables (e.g. a large volume) then it is certainly possible for the low-temperature gas to have more entropy than the high-temperature solid. Given other conditions (e.g. a small volume) then it is possible for the solid to have more entropy.

This is why sublimation occurs more at low pressure than at high pressure.
nouveau_riche
#52
Aug1-11, 10:22 AM
P: 253
Quote Quote by DaleSpam View Post
There is not enough information given. The entropy of a gas depends on other things besides just the temperature (and I don't know how to calculate the entropy of a solid):
http://hyperphysics.phy-astr.gsu.edu...entropgas.html

However, given the right conditions for the other variables (e.g. a large volume) then it is certainly possible for the low-temperature gas to have more entropy than the high-temperature solid. Given other conditions (e.g. a small volume) then it is possible for the solid to have more entropy.

This is why sublimation occurs more at low pressure than at high pressure.
yes entropy can be high even if the system has high thermal energy
you described well for my original question,thanks
just last think that still is doubtful-does SLOT was verified in my original question,it was clear that the temperature of water in bucket and in air both goes down,but what about entropy?
DaleSpam
#53
Aug1-11, 10:56 AM
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Quote Quote by nouveau_riche View Post
does SLOT was verified in my original question,it was clear that the temperature of water in bucket and in air both goes down,but what about entropy?
Entropy goes up.


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