Inert Gas Solubility in Water 2

[Mike4chemic]

Hello,

For our client, I try to perform the solubility calculations of the inert gases such as argon, nitrogen and hydrogen in geothermal water at 300 deg.F .One of the sources I am using is an article "Solubilities of inert gases in water 0 deg.C to near the critical point of water" by Himmelbau, D.M.
One of figure in the article ( the figure is attached)presents that solubility of argon,methane, nitrogen and hydrogen in water increases with the increase in temperature. Does is make sence?





Thanks in advance, Mike

 

[bimr]

Because solubility of gases usually decreases with increasing temperature at around room temperature, the partial pressure a given gas concentration has in liquid must increase. While heating water (saturated with nitrogen) from 25 to 95 °C, the solubility will decrease to about 43% of its initial value. This can be verified when heating water in a pot; small bubbles evolve and rise long before the water reaches boiling temperature. Similarly, carbon dioxide from a carbonated drink escapes much faster when the drink is not cooled because the required partial pressure of CO2 to achieve the same solubility increases in higher temperatures. Partial pressure of CO2 in the gas phase in equilibrium with seawater doubles with every 16 K increase in temperature.

When the temperature of a system changes, the Henrys constant will also change. I believe that is what is shown in your chart.

 

[25362]

Mike4chemic, apparently your interpretation is correct. See:

http://www.dipic.unipd.it/faculty/canu/files/tmp/h2o2/vle/Pray52.pdf

 

[moltenmetal]

What the paper shows is correct: solubility of these gases at first decreases with increasing temperature and constant pressure to a minimum, then begins to increase again sharply. It MUST be so and is noted in the text at the end of the paper, as at the critical point these gases are MISCIBLE with supercritical water. Remember that at the critical point, there is no liquid phase and all properties of steam and condensed water merge, and all gases are infinitely miscible with one another.

This is an example of how it is often dangerous to extend our normal observations of the world too far into the realm of higher temperatures and pressures...Our simple model of the world based on atmospheric pressure observations tells us that the higher the temperature, the lower the solubility of any permanent (nonreactive) gas should be- and we would expect that to continue. But reality differs from our simple model!

 

[Mike4chemic]

Thank you very much. I am wondering to know, what is the physical explanation of this phenomenon, when the gas solubilty increases with temperature increase ? Are there another gases which present the same behavior?

Thank you, Mike

 

[25362]

IMHO, temperature effects on a non-reacting-gas solubility in liquid water are attributed to a balance of enthalpies: that needed to create liquid pockets (endothermic) and that released when the gas molecule gets occluded (exothermic)
Since water has pockets "already made" by hydrogen bonding the net process is exothermic. Le Chatelier's rule applies and gases are released upon heating.

With organic solvents that do not form hydrogen bonds (bridges) like water does, the solubility increases with temperature. This is the case of H₂, N₂, CO He and Ne in Cl₄C, benzene and acetone.

Water at 210^oC has the same dielectric coefficient (DC =33) as methanol at ambient conditions, and DC continues to drop upon heating. At even higher temperatures hydrogen bonds get distorted or broken, thus the process becomes endothermic.

CO₂ solubility in water shows a similar behavior with a minimum concentration vs temperature, depending on pressure.