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When a gas is dissolved in water does the state of gas changes ? We write it as aqueous but what is the state that exists ? does it has the properties of gases when it is dilluted ?

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Good question! For a solid dissolved in liquid, obviously the solid behaves as a liquid rather than as a solid, since its particles are separated and moving freely.

A gas, though, is defined as free to fill its container, unlike a liquid with a definite volume. Since a dissolved gas (as opposed to one chemically bound to a liquid) is free to disperse, e.g. $\ce{CO2}$ bubbling out of seltzer, one might still consider it gaseous, rather than liquid, just loosely bound to the liquid.

That said, in a closed container in equilibrium, or over a short time, dissolved gases do behave as liquids. One can pour $\ce{NH4OH}$ ($\ce{NH3}$ aq.) into $\ce{H2SO4}$ ( $\ce{SO3}$ aq.), and the majority of the dissolved gases stay in solution -- though some $\ce{NH3}$ gets out, leaving one tearing and coughing, if not done under a hood.

It appears to be a matter of definition, then if dissolved gases are considered as gas or liquid.

BTW, gases dissolved in solids, such as methane clathrate, are more tightly locked in place and may behave as solids until warmed.

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  • $\begingroup$ so when we have a reaction in water solution that produces co2 we put the sign (g) because the container is open ? $\endgroup$ – ado sar Dec 13 '18 at 21:18
  • $\begingroup$ Yes... most of the CO2 bubble out quickly as a gas. On the other hand, if NH3 is evolved, it stays in solution longer, though it, too, comes out of solution. React CO2 with NH3, and it stays dissolved, as ammonium carbonate, so the answer is not always obvious. $\endgroup$ – DrMoishe Pippik Dec 13 '18 at 23:57

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