[sprotz]

What happens when hydrochloric acid is added to potassium carbonate in a sealed bottle? Does the reaction give off co2 that builds up pressure, and does the reaction stop at a certain pressure or does the reaction continue until all the co2 is released?

[chenbeier]

It will continue until all CO₂ is released. Pressure rises.  You get a sparkling salty water or the bottle explode before.

[AWK]

It all depends on the molar ratio of HCl:K₂CO₃ and the order of the addition of reagents.
If HCl is less than 1 mol to 1 mol of K₂CO₃ then at good mixing no CO₂ will evolve.
K₂CO₃ + HCl = KHCO₃ + KCl.
At a molar ratio of HCl>1 to 2, potassium carbonate will decompose with the evolution of CO₂.
KHCO₃ + HCl = KCl + H₂O + CO₂
This explanation applies to the addition of acid to carbonate.

In the reverse order of the addition of the reagent, potassium carbonate will decompose with the evolution of carbon dioxide until the molar ratio of HCl:K₂CO₃ will reach 2:1 or until the acid runs out.
K₂CO₃ + 2HCl = 2KCl + H₂O + CO₂
With excess potassium carbonate in a sealed vessel, the following reaction will occur:
CO₂ + K₂CO₃ + H₂O = 2KHCO₃

Even such a simple reaction can be so complicated.

[sprotz]

Thanks for the information. Because I learned that rate of co2 emission decreases with increase in pressure and eventually stops in case of a carbonate with acetic acid. Maybe with a stronger acid the threshold is higher? So if co2 continues to form and pressure rises, would this be an easy way to collect and store co2 in a pressurized tank, maybe liquid co2 will form if pressure gets high enough?

[Enthalpy]

Liquid CO₂ can exist up to 31°C, but it needs 74bar there, which most "bottles" don't resist.

Easier ways exist to obtain liquid CO₂, in case it's useful.