What happens to the concentration of carbonic acid when the pressure drops after opening a sealed, pressurized carbonated beverage container?
The equilibrium shifts back toward dissolved gas and water, decreasing acid concentration.
The process of opening a carbonated drink container results in an immediate drop in external pressure. Since the initial high pressure forced a large amount of $ ext{CO}_2$ into solution, creating carbonic acid, reducing this pressure causes the excess $ ext{CO}_2$ to escape rapidly as visible fizz. This release of $ ext{CO}_2$ drives the chemical equilibrium backward. As the system seeks balance under the new, lower pressure, the concentration of carbonic acid ($ ext{H}_2 ext{CO}_3$) simultaneously decreases as the components revert back toward dissolved $ ext{CO}_2$ and $ ext{H}_2 ext{O}$. This instability explains why carbonic acid is inherently unstable in open containers.
