|
Cepheus
Balance




Registered: 04/19/06
Posts: 8,266
Loc: the space between reality...
Last seen: 1 month, 20 days
|
Latent Heat Capacity
#8410239 - 05/16/08 05:01 PM (16 years, 6 days ago) |
|
|
The definition of Latent heat capacity is the amount of energy released when 1kg of a substance changes state (i.e from a liquid to a solid) whilst the temperature remains the same.
This seems somewhat paradoxical to me; temperature is energy..
Can someone explain this phenomena to me?
-------------------- "I only ever hope to reach equilibrium, in Nature's matrix, in line with the meridian" ~ Jehst
"...and I know that I have to keep breathing, as tomorrow the sun will rise, who knows what the tide will bring?" Free Spore Ring Europe Send any spare spore prints you might have and help the distribution
Open Source. Freedom. GNU/Linux Addicting is not a word.
|
DieCommie


Registered: 12/11/03
Posts: 29,258
|
Re: Latent Heat Capacity [Re: Cepheus]
#8410258 - 05/16/08 05:07 PM (16 years, 6 days ago) |
|
|
Temperature is not the only form of energy. Other energy is bound up in various bonds. So, for example liquid water, the molecules are bound up and in lower energy state from hydrogen bonding and the like. The extra energy from heating breaks those bonds and raises the water molecule into a un-bound state, steam. Now that it is un-bound, or free, heat energy goes into kinetic.
I dont know know if that made sense, its something like that.
|
Cepheus
Balance




Registered: 04/19/06
Posts: 8,266
Loc: the space between reality...
Last seen: 1 month, 20 days
|
Re: Latent Heat Capacity [Re: DieCommie]
#8410305 - 05/16/08 05:20 PM (16 years, 6 days ago) |
|
|
But the energy required to break the hydrogen bonds would heat the system..
I understand it in principal.. but just not how it works practically..
-------------------- "I only ever hope to reach equilibrium, in Nature's matrix, in line with the meridian" ~ Jehst
"...and I know that I have to keep breathing, as tomorrow the sun will rise, who knows what the tide will bring?" Free Spore Ring Europe Send any spare spore prints you might have and help the distribution
Open Source. Freedom. GNU/Linux Addicting is not a word.
|
DieCommie


Registered: 12/11/03
Posts: 29,258
|
Re: Latent Heat Capacity [Re: Cepheus]
#8410351 - 05/16/08 05:35 PM (16 years, 6 days ago) |
|
|
Quote:
Cepheus said: But the energy required to break the hydrogen bonds would heat the system..
And the hot molecules escape, and the substance is left cooler via this evaporation. Then its heated by the source, until more water molecules break free. This process, statistically averaged has a constant temperature, until all the hydrogen bonds are broke.
|
spock1
Stranger


Registered: 04/14/07
Posts: 589
Last seen: 15 years, 10 months
|
Re: Latent Heat Capacity *DELETED* [Re: Cepheus]
#8410362 - 05/16/08 05:40 PM (16 years, 6 days ago) |
|
|
Post deleted by spock1Reason for deletion: .
|
Cepheus
Balance




Registered: 04/19/06
Posts: 8,266
Loc: the space between reality...
Last seen: 1 month, 20 days
|
Re: Latent Heat Capacity [Re: spock1]
#8410433 - 05/16/08 06:02 PM (16 years, 6 days ago) |
|
|
Ok, that makes sense.
So how does a liquid go to a solid without changing temperature? .. Does it just spontaeneously loose all that PE and stop vibrating?
-------------------- "I only ever hope to reach equilibrium, in Nature's matrix, in line with the meridian" ~ Jehst
"...and I know that I have to keep breathing, as tomorrow the sun will rise, who knows what the tide will bring?" Free Spore Ring Europe Send any spare spore prints you might have and help the distribution
Open Source. Freedom. GNU/Linux Addicting is not a word.
|
DieCommie


Registered: 12/11/03
Posts: 29,258
|
Re: Latent Heat Capacity [Re: Cepheus]
#8410447 - 05/16/08 06:07 PM (16 years, 6 days ago) |
|
|
When you cool it to a solid, the individual molecules lose some of their kinetic. This allows the intermolecular forces to over power the kinetic thats left over. The intermolecular forces then position the molecules in a lattice, because thats a lower energy state and then you have a solid.
|
Cepheus
Balance




Registered: 04/19/06
Posts: 8,266
Loc: the space between reality...
Last seen: 1 month, 20 days
|
Re: Latent Heat Capacity [Re: DieCommie]
#8410582 - 05/16/08 06:53 PM (16 years, 6 days ago) |
|
|
But you're cooling it...
-------------------- "I only ever hope to reach equilibrium, in Nature's matrix, in line with the meridian" ~ Jehst
"...and I know that I have to keep breathing, as tomorrow the sun will rise, who knows what the tide will bring?" Free Spore Ring Europe Send any spare spore prints you might have and help the distribution
Open Source. Freedom. GNU/Linux Addicting is not a word.
|
DieCommie


Registered: 12/11/03
Posts: 29,258
|
Re: Latent Heat Capacity [Re: Cepheus]
#8410625 - 05/16/08 07:15 PM (16 years, 6 days ago) |
|
|
Yea.. are you asking how something can cool down? You place a cooler reservoir next to it and it will absorb kinetic energy from the hotter reservoir until they are in equilibrium. If that equilibrium is cold enough, inter molecular forces dominate and a lattice forms (or an amorphous solid).
The temperature stays the same because at the point where the solid forms, the coldest atoms become part of the solid and the liquid ones are left over, and are still warm. Then they lose their energy to the cold reservoir and get absorbed by the solid. This continues until there are no liquid atoms left, and then the temperature can continue to drop in the now solid substance.
Hope some of that made sense.
|
spock1
Stranger


Registered: 04/14/07
Posts: 589
Last seen: 15 years, 10 months
|
Re: Latent Heat Capacity *DELETED* [Re: DieCommie]
#8410844 - 05/16/08 08:21 PM (16 years, 6 days ago) |
|
|
Post deleted by spock1Reason for deletion: .
|
johnm214



Registered: 05/31/07
Posts: 17,582
Loc: Americas
|
Re: Latent Heat Capacity [Re: spock1]
#8410947 - 05/16/08 08:49 PM (16 years, 6 days ago) |
|
|
Quote:
Cepheus said: Ok, that makes sense.
So how does a liquid go to a solid without changing temperature? .. Does it just spontaeneously loose all that PE and stop vibrating?
One thing that might help is to realize that to have an isothermal phase change you have to have an infinitly slow heat (energy) transfer, so it really doesn't happen.
Melting ice, i.e., you slowly provide energy that is absorbed by the matter and since it takes energy to break the hydrogen bonds of the ice, the matter uses the energy as you supply it.
Also remember, by definition, at equilibrium w/ two phases of matter, the temperature is the temperature at which they transition. So water and ice should be 0C at equilibrium.
So if you supply heat at an infinitely slow rate, none of that heat is used to raise the temperature, ideally. Because of entropy, the system wants to be all at the same energy state. Water is higher energy than ice, so the energy flows from the water to the ice. As ice takes energy to melt, the melting ice in turn cools the system by the exact amount of the heat required to melt it (remember, it takes the same energy to melt ice as form ice, the signs are just reversed). So the heat supplied by the system is taken by the ice, so there is no net gain of temperature, cuz all the heat tends to flow into the ice and be transfered into kinetic energy to break the hydrogen bonds. Sort of how like 0C ice seems colder than 0C water, the ice will actually absorb heat without changing temperature, while the water has to change temperature if it absorbs heat, cuz there is no physical/chemical buffering going on.
If your knowledgable about acid base buffers, its the exact same thing, almost. The pH of the solution won't change much untill you've practically exhausted your buffering agent, even when adding an acid, cuz the protons are absorbed by a base w/ a weak conjugate acid, only w/ the stuff your talking about the proton is the heat, the strong acid is the heating element and the weak conjugate acid is the water(the conjugate base the ice) -_- Just figured you were in gen chem or something and might help, but that was kinda silly in retrospect
So any mixture of ice and water is always 0C or thereabouts unless its pretty far from equilibrium. This is why a glass w/ fifty icecubes isn't any colder than the same glass some hours later w/ only one sliver of ice cube in it, ideally.
|
Cepheus
Balance




Registered: 04/19/06
Posts: 8,266
Loc: the space between reality...
Last seen: 1 month, 20 days
|
Re: Latent Heat Capacity [Re: johnm214]
#8412096 - 05/17/08 07:09 AM (16 years, 6 days ago) |
|
|
Right I get it now 
It understood it in terms of entropy (thats what I break down most physical systems to in order to attempt to understand them).
I just didn't get the actual mechanism (I was zoning out when my physics teacher explained it ).
Good work
-------------------- "I only ever hope to reach equilibrium, in Nature's matrix, in line with the meridian" ~ Jehst
"...and I know that I have to keep breathing, as tomorrow the sun will rise, who knows what the tide will bring?" Free Spore Ring Europe Send any spare spore prints you might have and help the distribution
Open Source. Freedom. GNU/Linux Addicting is not a word.
|
|