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Post by duwayne on Sept 23, 2019 2:40:17 GMT
Yesterday, I went to a ground-breaking ceremony at a college near where I grew up. The new building is an addition to the main science facility and the head science professors and top students were there to thank the donors. After the ceremonies, I got a chance to separately ask the head of the science department and a bright physics student about the molecular mechanics of latent heat. In separate conversations they both gave me the same answer. As liquids, the H2O molecules are bonded to each other. Considerable energy is required to free a water vapor molecule from its liquid neighbors. This energy is provided from the sensible heat in the liquid molecules which surround the “freed” water vapor molecule. The energy breaks the bonds but it is not actually taken away by the water vapor molecule. On condensation, something similar to a chemical reaction occurs. The water vapor molecule bonds (reacts) with the liquid molecules and gives off heat which is captured by the liquid molecules as sensible heat. I also talked to another student about "slow light". As we all know light (photons) travel at about 186,000 miles per second in air. She has found a material through which light travels at much slower speeds. Light can be shined onto a block of this material and the light will pass through, but it will takes a few seconds to do so. Honest I am not being argumentative I really want to know - but this seems like hand waving. So the first 'evaporation' the sensible heat 'frees' the evaporating molecule but it does not take away any heat.... So there is no such thing as evaporative cooling? The reason we sweat is to loose heat by evaporative cooling as the evaporating molecules remove the latent heat of evaporation. This is not true? Then the molecule that did not take any heat away, condenses and gives the heat it did not take away to the liquid molecules it condensed onto? It would be really really useful for someone to document the flow of latent heat and storage of latent heat without using words like provide, release, and even sensible heat(which is transference of heat from (somewhere in the molecule to somewhere in another molecule); but instead saying that the heat stored as (name how it is stored) is transferred to (heat sink) by (method of transference) where it is stored as (description of heat storage) or how the molecule loses heat that is how the storage for the heat transfers the heat from the molecule and the way it leaves the molecule. Nautonnier, when liquid water gives up sensible heat as I described above, the result is the liquid water that gives up the sensible heat will be cooler. I thought you knew that or I would have said it. Evaporation results in cooling of the liquid water that is left behind. If I were to paraphrase the rest of your post, it would be “I (Nautonnier) don’t understand molecular bonds. Can someone explain the molecular mechanics of latent heat without mentioning bonds.” I’m not going to try to explain beyond what I did in the post above since that describes the molecular mechanics. But I will ask this. If you have a tank of natural gas and open the valve and light it with a match, a lot of heat will be generated. No atoms will be destroyed in the process. They will end up in the carbon dioxide and water produced. Where does that heat come from? It’s not from the match. It’s not from phlogiston. The heat comes from somewhere else.
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Post by nautonnier on Sept 23, 2019 19:03:10 GMT
Honest I am not being argumentative I really want to know - but this seems like hand waving. So the first 'evaporation' the sensible heat 'frees' the evaporating molecule but it does not take away any heat.... So there is no such thing as evaporative cooling? The reason we sweat is to loose heat by evaporative cooling as the evaporating molecules remove the latent heat of evaporation. This is not true? Then the molecule that did not take any heat away, condenses and gives the heat it did not take away to the liquid molecules it condensed onto? It would be really really useful for someone to document the flow of latent heat and storage of latent heat without using words like provide, release, and even sensible heat(which is transference of heat from (somewhere in the molecule to somewhere in another molecule); but instead saying that the heat stored as (name how it is stored) is transferred to (heat sink) by (method of transference) where it is stored as (description of heat storage) or how the molecule loses heat that is how the storage for the heat transfers the heat from the molecule and the way it leaves the molecule. Nautonnier, when liquid water gives up sensible heat as I described above, the result is the liquid water that gives up the sensible heat will be cooler. I thought you knew that or I would have said it. Evaporation results in cooling of the liquid water that is left behind. If I were to paraphrase the rest of your post, it would be “I (Nautonnier) don’t understand molecular bonds. Can someone explain the molecular mechanics of latent heat without mentioning bonds.” I’m not going to try to explain beyond what I did in the post above since that describes the molecular mechanics. But I will ask this. If you have a tank of natural gas and open the valve and light it with a match, a lot of heat will be generated. No atoms will be destroyed in the process. They will end up in the carbon dioxide and water produced. Where does that heat come from? It’s not from the match. It’s not from phlogiston. The heat comes from somewhere else. ALL descriptions of latent heat are that the molecule that changes phase (breaks weak bonds) with the remaining liquid molecules _does_ take the latent heat of evaporation away. What you appear to be saying is that the latent heat of evaporation is lost by the liquid which you admit cools due to the loss of this energy, but it is not taken away by the evaporating molecule - so where does it go? Not only that where does the energy come from that is 'released' when the water molecule condenses? I think I have as much knowledge as most of molecular bonds, weak and strong bonds, electron shells and the sharing of electrons etc But the amount of energy that is supposedly 'released' by a water molecule on phase change seems to be far more than could be 'stored' in a water molecule. Finding that you say this was not taken from the surface it evaporated from makes that even more confusing as where does the latent heat of condensation come from? It's significant as that is what drives thunderstorms and hurricanes.
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Post by acidohm on Sept 23, 2019 21:16:04 GMT
How much energy is required to excite a water molecule to become vapour?
How much does a water vapour molecule lose to re-bond as a water molecule?
The difference states require different energy, say a water molecule (wm) is 1 and a vapour (wv) 10.
When wm has gained 9 units of energy its wv. Where does this 9 come from, it has to be the surrounding environment because demonstrably this cools.
What is the environment? It might be the wet cloth around your sprained ankle, ocean surface, other wm on a nucleus in a cloud.
Vice versa for condensation, wv 10 loses 9 to the environment to re-bond hydrogen bonds to become 1 again.
The hydrogen bond is the attraction of + to - outer electron shells of hydrogen and oxygen in different water molecules.
An excited (warm) molecule becomes too energetic for the bond to hold at a certain point and the bond becomes un-viable, releasing the excited molecule to wv.
Id say imagine pulling 2 magnets apart, it takes a certain amount of effort and once free, you could pass the magnets quickly past each other but the meeting is to brief to allow re-attachment, only if you lose energy, ie, pass slower, will they re-attach/bond There must be some conduction within a droplet for example whereby a molecule in the middle loses its energy to more free molecules at the periphery, but perhaps this idea violates some thermodynamic principles??
Id imagine once wv the molecules have considerable greater kinetic energy?
I can see alot of chaotic principles underlying the whole process regarding differing mediums that may be present in a wm vicinity muddying a basic process into many complicated ones.
Overall, i dont see latent heat as a question of how energy is stored, rather a transfer of it from state change, and what each state of water is.
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Post by duwayne on Sept 24, 2019 0:12:13 GMT
Nautonnier, when liquid water gives up sensible heat as I described above, the result is the liquid water that gives up the sensible heat will be cooler. I thought you knew that or I would have said it. Evaporation results in cooling of the liquid water that is left behind. If I were to paraphrase the rest of your post, it would be “I (Nautonnier) don’t understand molecular bonds. Can someone explain the molecular mechanics of latent heat without mentioning bonds.” I’m not going to try to explain beyond what I did in the post above since that describes the molecular mechanics. But I will ask this. If you have a tank of natural gas and open the valve and light it with a match, a lot of heat will be generated. No atoms will be destroyed in the process. They will end up in the carbon dioxide and water produced. Where does that heat come from? It’s not from the match. It’s not from phlogiston. The heat comes from somewhere else. ALL descriptions of latent heat are that the molecule that changes phase (breaks weak bonds) with the remaining liquid molecules _does_ take the latent heat of evaporation away. What you appear to be saying is that the latent heat of evaporation is lost by the liquid which you admit cools due to the loss of this energy, but it is not taken away by the evaporating molecule - so where does it go? Not only that where does the energy come from that is 'released' when the water molecule condenses? I think I have as much knowledge as most of molecular bonds, weak and strong bonds, electron shells and the sharing of electrons etc But the amount of energy that is supposedly 'released' by a water molecule on phase change seems to be far more than could be 'stored' in a water molecule. Finding that you say this was not taken from the surface it evaporated from makes that even more confusing as where does the latent heat of condensation come from? It's significant as that is what drives thunderstorms and hurricanes. Nautonnier, you seem to be repeating a lot of things I said on earlier threads about the importance of latent heat and how it works in an overall sense. I hope you no longer believe that latent heat is released as radiation on condensation. I'm still not sure why you want to try to understand the molecular physics of latent heat but I've been willing to discuss this since it seems to be of some importance to you. Let’s see if we can agree on one thing and then I'll try another explanation. When natural gas burns, CO2 and water vapor are produced. At formation the water vapor has never been in a liquid form. This water vapor molecule is exactly the same as a water vapor molecule that was evaporated from a liquid form. Would you agree that there is no chemical, structural or energy difference between a water vapor molecule produced from burning natural gas and one evaporated from liquid water? Yes or no?
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Post by acidohm on Oct 3, 2019 19:51:21 GMT
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Post by blustnmtn on Mar 8, 2020 12:07:44 GMT
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Post by Ratty on Mar 8, 2020 13:47:17 GMT
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Post by nonentropic on Mar 8, 2020 18:08:02 GMT
What a surprise the tropics are very close to temperature stable.
So storms get bigger? or smaller? when the poles get warmer but the tropics stay the same temperature. We could build a measure of global temperature where more storms are a proxy for cooling climate.
That would stuff them up!
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Post by nautonnier on Mar 8, 2020 18:32:29 GMT
The paper is also on Research Gate which I can access - I will see if they also add that the enthalpy of the moist air is significantly higher due to the latent heat of water. So moist air can hold far more energy than dry air and it is lighter so carries that energy upward until it reaches its condensation point. That is where the 'discussions' break out about what the water molecule does with its latent heat payload as it condenses. Even the most esoteric and technical papers resort to handwaving and say 'the latent heat is released'
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Post by nonentropic on Mar 8, 2020 20:02:02 GMT
the moisture buffers the temperature drop as it rises due to its buoyancy thus speeding it rise.
Yes overlooked, but the discussion about outgoing radiation ignores the massive transport of heat from lower down to the upper atmosphere thus bypassing the "greenhouse effect".
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