If I could somehow instantaneously replace the $\ce{CO2}$ gas cap at the top of a soda bottle with a different gas, say $\ce{N2}$, would the bottle pressure increase as a result of the $\ce{CO2}$ de-gassing into the gas cap space?

I've come to this question because I am trying to design a method to measure the dissolved $\ce{CO2}$ content of a water liquid stream. The method involves exsolving the $\ce{CO2}$ into either an evacuated or $\ce{N2}$-charged vessel and measuring the pressure change to correlate dissolved $\ce{CO2}$. By Henry's Law the pressure in an $\ce{N2}$-charged vessel should increase as a result of $\ce{CO2}$ exsolving since the $\ce{CO2}$ partial pressure above the liquid is zero, should it not?

More clarification (hopefully) for those who have marked the question as unclear: Let's say I have a closed system (soda water in a bottle as an example) with a $\ce{CO2}$ gas cap at a pressure of 10 psig. The gas cap, like in a soda bottle, is small relative to the total volume, say 5%. The liquid (water) in the bottle is fully saturated with dissolved $\ce{CO2}$. Now let's say I somehow instantaneously replace the $\ce{CO2}$ in the gas cap with another gas, say $\ce{N2}$, at the same pressure (10 psig). The system is still closed (we've magically replaced that gas). Will the bottle pressure increase as a result of the $\ce{CO2}$ in solution exsolving into the gas cap space, since the partial pressure of $\ce{CO2}$ there is zero? This of course is hypothethical, but it would have some similarity to how the dissolved gas content of liquids drawn (pumped) from deep within a well could be measured.


  • $\begingroup$ Guinness beer will do. $\endgroup$ – Ivan Neretin Jun 11 '19 at 19:24
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    $\begingroup$ Please see my updated description, thanks $\endgroup$ – prairieDog Jun 11 '19 at 21:36
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    $\begingroup$ @IvanNeretin I had to look it up: allaboutbeer.com/man-invented-nitro-guinness $\endgroup$ – Karsten Theis Jun 11 '19 at 22:24
  • $\begingroup$ To the point of the question: yes, it will increase. $\endgroup$ – Ivan Neretin Jun 12 '19 at 7:35
  • $\begingroup$ Ok, thanks. Love the Guinness angle too... $\endgroup$ – prairieDog Jun 12 '19 at 14:05

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