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Author Topic: Is releasing water from ringwoodite endothermic?  (Read 323 times)

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KenJackson

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Is releasing water from ringwoodite endothermic?
« on: November 11, 2017, 04:31:52 PM »

From Wikipedia:
Quote
Ringwoodite is a high-pressure phase of Mg2SiO4 formed at high temperatures and pressures ...
Ringwoodite is notable for being able to contain hydroxide ions (oxygen and hydrogen atoms bound together) within its structure.

I want to know if I am correct that releasing water from soaked crystals is endothermic.
I guess there's two steps--releasing the OH ions, and then converting them to water and oxygen.
I don't know how to begin.
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KenJackson

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Re: Is releasing water from ringwoodite endothermic?
« Reply #1 on: November 17, 2017, 04:57:37 AM »

I've made a little progress.

If we start with four OH- ions, we have to break two O-H bonds and form two new O-H bonds to get two water molecules, which I believe is energy neutral. But when we combine the remaining oxygen atoms into O2, we release some energy, maybe 495 kJ/mol.

But that's not all there was. The ringwoodite is "able to contain hydroxide ions", but what does that mean? Things tend to go to the lowest energy state, so I expect the crystal holding hydroxide is in a lower energy state than having the two separate.

So separating the hydroxide from the crystals should take energy.  But how much energy?  If it takes more than 495/4 kJ/mol of OH- ions, then the overall process would be endothermic.  Right?

So how can we know how much energy it takes to separate OH- from Mg2SiO4?  What do I even google for?
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Corribus

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Re: Is releasing water from ringwoodite endothermic?
« Reply #2 on: November 17, 2017, 07:24:55 AM »

I think you're not getting a whole lot of bites because you haven't clearly defined what process you are evaluating. I don't know what "releasing water from soaked crystals" means, nor how that relates to "releasing OH ions, and then converting them to water and oxygen".

In order to understand the thermodynamics of a process, you have to articulate what the process actually is and what the structures involved are.  You haven't really done this - just quoted two sentences from a Wikipedia article.
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Arkcon

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Re: Is releasing water from ringwoodite endothermic?
« Reply #3 on: November 17, 2017, 09:16:07 AM »

I'm sorry KenJackson:, that you haven't had more help with this question so far.  But like Corribus: said, you're really not being clear.  I suspect the problem is just as much with this particular Wikipedia definition.  Let's try to break apart your question,and see if our Physical Chemistry masters can help us -- because I'm out of my depth here.

From Wikipedia:
Quote
Ringwoodite is a high-pressure phase of Mg2SiO4 formed at high temperatures and pressures ...

OK.  That's simple enough. I can follow that much.

Quote
Ringwoodite is notable for being able to contain hydroxide ions (oxygen and hydrogen atoms bound together) within its structure.

OK.  Wikipedia says that's notable.  But is that really notable?  Sodium hydroxide is a solid, it has -OH groups within its structure. Copper Sulfate pentahydrate has water molecules in its crystal structure.  We call carbohydrates that just because when we heat them,water comes off, leaving carbon, sugars exist as molecules with -OH groups as well.

Maybe this Wikipedia statement says nothing at all.  Kids edit Wikipedia, and many feel like giving a "high school term paper" definition is awesome.  Or maybe this is a poor translation from another language.

Quote
I want to know if I am correct that releasing water from soaked crystals is endothermic.

Annnd, that is a possibility, or it may not be the case.  But you may not be able to say anything from the quotes you have.

Quote
I guess there's two steps--releasing the OH ions, and then converting them to water and oxygen.

And, that's not how we release water from the examples I gave above.

Quote
I don't know how to begin.

Well,you've made up some chemistry above, and also in your second posting, but we can still get to the answer you need. But there will need to be some more baby steps of knowledge to get ready.  But we're here to help.
« Last Edit: November 17, 2017, 02:42:05 PM by Arkcon »
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