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Topic: mechanism of gas solubility?  (Read 3203 times)

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Offline iScience

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mechanism of gas solubility?
« on: July 28, 2013, 02:44:37 PM »
what is the mechanism of solubility for gases?

i've been reading online and apparently there are 'pockets' in the solvent required to be present for gas constituents to be absorbed.

(i was reading http://antoine.frostburg.edu/chem/senese/101/solutions/faq/temperature-gas-solubility.shtml#mysels)

what pocket is it talking about? there are many grooves on the surface of the liquid. is the 'pocket' referring to the formation of an instantaneous well that one gas particle could fit in?

and could someone clear up the confusion i'm having about energy absorption being related to solubility?
eg, how is more heat released the stronger the intermolecular attractions are between the solvent and gas moleucles? how does this lead to the understanding of solubility of gases and temperature change?

Offline Corribus

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Re: mechanism of gas solubility?
« Reply #1 on: July 29, 2013, 09:46:20 AM »
Solubility of gasses is not so different from solubility of solids.  The biggest difference is that it can be fairly entropically unfavorable, since gasses have pretty high entropy.  If the interactions between the gas molecules and the liquids is pretty strong, though, this can compensate.  You can also get a positive gain in entropy if solvent molecules become highly ordered around solubilized gasses. 

The reason heat is released is the same reason you get heat release when you form any bond.  Bonding is generally a lower energy state than not-bonding.  Since you are going from a relatively high energy state to a relatively low energy state, the difference is released to the environment as heat.
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

Offline curiouscat

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Re: mechanism of gas solubility?
« Reply #2 on: July 29, 2013, 10:22:13 AM »
  You can also get a positive gain in entropy if solvent molecules become highly ordered around solubilized gasses. 

Do you know any specific cases where this is a dominant  mechanism?

Offline Corribus

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Re: mechanism of gas solubility?
« Reply #3 on: July 29, 2013, 11:34:58 AM »
No, I don't.  I was just speaking generally.  I don't know of a specific situation where the positive entropy gain by solvent reorganization around a dissolved gas molecule exceeds the entropy loss from confining a gas molecule in a liquid.  That's not to say there aren't examples, though.  Perhaps something like ammonia gas, which is capable of hydrogen bonding, might be an example?

To the OP, another "unusual" thing about gas solubility is that it often drops as temperature increases... unlike what is usually (though not always) observed for solid solutes.  Oxygen, for example, is more soluble in cooler water.  On the other hand, solid salts behave in opposite fashion.  You might guess at the entropic favorability of oxygen dissolution and salt dissolution in water by these different observed trends.
What men are poets who can speak of Jupiter if he were like a man, but if he is an immense spinning sphere of methane and ammonia must be silent?  - Richard P. Feynman

Offline curiouscat

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Re: mechanism of gas solubility?
« Reply #4 on: July 29, 2013, 12:06:35 PM »
No, I don't.  I was just speaking generally.  I don't know of a specific situation where the positive entropy gain by solvent reorganization around a dissolved gas molecule exceeds the entropy loss from confining a gas molecule in a liquid.  That's not to say there aren't examples, though.  Perhaps something like ammonia gas, which is capable of hydrogen bonding, might be an example?

Ok, thanks. It just seemed like a mode that seemed a bit alien to me.

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