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Old 05-01-2017, 06:07 AM
 
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Take NaCl which is common table salt. It's melting point is 801C (= 1474F) which is what it takes to put it into liquid form.

Take NaCl and dissolve it in water at room temperature (about 68F) which my text says is due to hydrogen bonding breaking down the ionic bonds. This second way appears to put the salt in the same liquid state as the first way of melting.

Due to the tremendous temperature difference, it seems to suggest the potential of deriving energy from hydrogen bonding which may be substantial since water covers 71% of the earth. A check of the internet has turned up nothing on this so I'm wondering if someone else has checked this out further and has knowledge to share?
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Old 05-01-2017, 09:36 AM
 
Location: Somewhere in northern Alabama
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A simple way to estimate the harvestable energy is to measure the temperatures when a salt goes into solution. On a basic level, energy = heat. Table salt added to water changes the temperature only slightly. The reaction of calcium chloride, however, is significantly exothermic when water is added.
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Old 05-09-2017, 03:13 PM
 
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A few things are wrong about the original post:


While hydrogen bonding is related to the fact that water is a polar molecule, and solvation of NaCl is also related to the fact that water is polar, dissolution of NaCl is not due to hydrogen bonding.


Hydrogen bonding is an interaction between water molecules, not an interaction between water molecules and NaCl. In other words, hydrogen bonding is an intermolecular force, while dissolution of NaCl is due to intramolecular (polarity) forces.


Upon dissolution, the negative end of a group of water molecules will surround the positively charged Na+ ion. Similarly, the positive end of a group of water molecules will surround the negatively charged Cl- ion. So, it is more likely hydrogen bonding is destroyed during dissolution of NaCl.


Also, melting NaCl to a liquid is a different physical process than is dissolution in water. In the case of melting, the NaCl is still interacting with each other, but there is enough heat energy to allow intermolecular motion. In the case of dissolving NaCl in water, the interaction in now between Na+ and water and Cl- and water.


Alas, this idea wont work. Also, the oceans are already salty and therefore already have dissolved salts. It will take energy to go the other way (salt water ---> fresh water) indeed reverse osmosis machines do need to be plugged in. If that is the case you can then get energy via regular osmosis (but this has nothing to do with dissolving or melting the salt, just going from fresh water to salty water).
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Old 05-09-2017, 06:33 PM
 
432 posts, read 146,370 times
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Quote:
Originally Posted by Greybear View Post
A few things are wrong about the original post:


While hydrogen bonding is related to the fact that water is a polar molecule, and solvation of NaCl is also related to the fact that water is polar, dissolution of NaCl is not due to hydrogen bonding.


Hydrogen bonding is an interaction between water molecules, not an interaction between water molecules and NaCl. In other words, hydrogen bonding is an intermolecular force, while dissolution of NaCl is due to intramolecular (polarity) forces.


Upon dissolution, the negative end of a group of water molecules will surround the positively charged Na+ ion. Similarly, the positive end of a group of water molecules will surround the negatively charged Cl- ion. So, it is more likely hydrogen bonding is destroyed during dissolution of NaCl.


Also, melting NaCl to a liquid is a different physical process than is dissolution in water. In the case of melting, the NaCl is still interacting with each other, but there is enough heat energy to allow intermolecular motion. In the case of dissolving NaCl in water, the interaction in now between Na+ and water and Cl- and water.


Alas, this idea wont work. Also, the oceans are already salty and therefore already have dissolved salts. It will take energy to go the other way (salt water ---> fresh water) indeed reverse osmosis machines do need to be plugged in. If that is the case you can then get energy via regular osmosis (but this has nothing to do with dissolving or melting the salt, just going from fresh water to salty water).
I checked and you're correct about the hydrogen bonding. The rest of the post still stands. When you compare the melting and the dissolving of the salt, the atoms go from a solid state where their positions are fixed to a liquid state where the atoms freely move. Of course you're correct when you say the oceans are salty. I used the oceans as an example as to how common water is. Water evaporates to form the clouds which then rains which is mostly free of salt.

The biggest difference between the melting and the dissolving is the temperature which is 1474F for melting salt as opposed to 68F (room temperature) to dissolve it. The question is why does this difference occur? And can it lead to a new source of energy? So I'm exploring the possibility.
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Old 05-10-2017, 12:12 PM
 
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Quote:
Originally Posted by education explorer View Post
I checked and you're correct about the hydrogen bonding. The rest of the post still stands. When you compare the melting and the dissolving of the salt, the atoms go from a solid state where their positions are fixed to a liquid state where the atoms freely move. Of course you're correct when you say the oceans are salty. I used the oceans as an example as to how common water is. Water evaporates to form the clouds which then rains which is mostly free of salt.

The biggest difference between the melting and the dissolving is the temperature which is 1474F for melting salt as opposed to 68F (room temperature) to dissolve it. The question is why does this difference occur? And can it lead to a new source of energy? So I'm exploring the possibility.



I see what you are saying, and I respect you for exploring the possibility and looking into ways in which we can solve our energy needs. I implore you to get as educated in chemistry and physics as you can and work on this problem.


The bolded statement where you compare the melting of the salt to the dissolution of salt as both being the same thermodynamic process is not accurate. Solvation of salt is not the same as melting it. You are comparing apples to oranges in these two processes as they are completely different. This can be observed empirically as the other poster mentioned.


Let me further explain theoretical considerations....


You are falsely assuming that the temperature difference between the two processes is the only thermodynamic variable one should consider and that melting NaCl and dissolving it in water is equivalent thermodynamically. Temperature can be used to evaluate the heat (enthalpy) of a system, but there are other forms of energy that need to be considered including...


1) Potential energy
2) work
3) entropy (disorder or chaos in a system)


Plus there are more interactions you need to think about too. Think of it this way...


When you melt the NaCl, you are adding enough energy to disrupt the interactions in the NaCl lattice so that the ions may become mobile with respect to each other and that's about all she wrote for that system. Entropy will also play a role in addition to heat as a liquid is more disordered than the solid.


When you dissolve NaCl in water, you are not only disrupting the interaction of NaCl, but you are also disrupting the interaction between water molecules, then you are also creating new interaction of water molecules with Na+ and water with Cl-. Entropy also plays a role, but you cannot say its the same as melting because you have more players on the court.


So whatever amount of energy you are putting into disrupting the NaCl interactions, your getting back by the disruption/creation of interaction between water and between water and Na+ and Cl-.


How this play out depends on the system. If you dissolve alcohol in water you will get energy in the form of heat released and you can feel the heat if you touch the container this occurred in (assuming you add enough alcohol to the water).


However, if you dissolve KCl in water, a net amount of energy will be put into the system and the container will feel cold to touch.


In the end it is more complicated than just considering temperature.


If you were to consider just the energy from dissolving NaCl into water, than in essence, the opposite process (removing the water from a solution of NaCl/water) already happens when the sun separates water from the salty oceans, then it rains inland, then the water moves downhill back toward the ocean and through hydroelectric dams, therefore, we are already in effect harnessing this energy.
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Old 05-12-2017, 08:18 AM
 
432 posts, read 146,370 times
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What caught my eye in this article (3rd paragraph) is
"water at room temperatures" which leads to a better process in the laboratory. How closely this ties into the temperature difference as I described before, I don't know since I don't know the mechanisms, but clearly water has some property that allows processes to be conducted at room temperature instead of high temperature as this article describes:

https://m.phys.org/news/2017-05-chea...conductor.html
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Old 05-18-2017, 10:11 AM
 
167 posts, read 439,171 times
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Quote:
Originally Posted by education explorer View Post
What caught my eye in this article (3rd paragraph) is
"water at room temperatures" which leads to a better process in the laboratory. How closely this ties into the temperature difference as I described before, I don't know since I don't know the mechanisms, but clearly water has some property that allows processes to be conducted at room temperature instead of high temperature as this article describes:

https://m.phys.org/news/2017-05-chea...conductor.html

Thanks for the link, some interesting work for sure. It should be noted though it isn't the power of water that is doing the process. Water is just the medium it takes place in. As I stated above, its not so much about the temperature as it is about the energy. That energy can be in the form of heat, but it can also be in other forms, in this case, electricity. Its essentially a type of electroplating, a common process.


From the article...


Quote:
To do this, Maldonado and his team make a thin, liquid metal film that rests on a substrate that they connect to a power supply.

Now using electricity rather than heat as the form of energy needed is a good step though, as I believe it is much more efficient.
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