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

[Dale]

Let me do a concrete hypothetical example.

Let's say we have a liquid phase of 3 molecules and a gas phase of 3 molecules, and let's say that in some units the KE of the liquid phase molecules is 10, 20, and 30, and for the vapor also 10, 20, and 30. Let's further say that the intermolecular forces in the liquid have an energy of 20.

Now the average KE for the liquid is 20 and the average KE for the vapor is also 20, so they are at the same temperature. If the liquid molecule with KE of 30 evaporates then the liquid phase now consists of two molecules of KE 10 and 20. The average KE has gone down to 15, so the temperature of the liquid has decreased.

The evaporated molecule had a KE 30 in the liquid, but due to the intermolecular forces it is slowed down to 10 in the vapor. So now the gas phase consists of four molecules of KE 10, 10, 20, 30. The average KE has gone down to 17.5, so the temperature of the vapor has also gone down.

With no external energy input evaporation will cause the temperature to decrease.

 

[nouveau_riche]

Let me do a concrete hypothetical example.

Let's say we have a liquid phase of 3 molecules and a gas phase of 3 molecules, and let's say that in some units the KE of the liquid phase molecules is 10, 20, and 30, and for the vapor also 10, 20, and 30. Let's further say that the intermolecular forces in the liquid have an energy of 20.

Now the average KE for the liquid is 20 and the average KE for the vapor is also 20, so they are at the same temperature. If the liquid molecule with KE of 30 evaporates then the liquid phase now consists of two molecules of KE 10 and 20. The average KE has gone down to 15, so the temperature of the liquid has decreased.

The evaporated molecule had a KE 30 in the liquid, but due to the intermolecular forces it is slowed down to 10 in the vapor. So now the gas phase consists of four molecules of KE 10, 10, 20, 30. The average KE has gone down to 17.5, so the temperature of the vapor has also gone down.

With no external energy input evaporation will cause the temperature to decrease.

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?

 

[Drakkith]

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?

Why would high entropy mean more energy?

 

[nouveau_riche]

Why would high entropy mean more energy?

the power to overcome intermolecular interactions

 

[Drakkith]

the power to overcome intermolecular interactions

Which explains entropy how?

 

[nouveau_riche]

Which explains entropy how?

the entropy of water molecule in air is more than in water

 

[Drakkith]

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]

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]

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]

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]

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]

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]

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]

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]

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
\DeltaG=\DeltaH-T\DeltaS

where \DeltaG is the useful energy available to do work
\DeltaH is the enthalpy change in the process
T equals the temperature in Kelvins
\DeltaS relates to the change in enthalpy.

Always remember that a negative value of \DeltaG gives us a spontaneous reaction!

 

[hacillunation]

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"?

 

[Dale]

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.

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]

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

 

[Dale]

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]

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)?

 

[Dale]

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/hbase/therm/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]

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/hbase/therm/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?

 

[Dale]

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.