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A friend explained to me that to prevent an opened soda bottle from going flat, the best course of action is to press the bottle before putting the cap back on as to chase air out of the bottle.

This seems counter-intuitive to me, since this should cause the air pressure to decrease inside the bottle (because the bottle tends to snap back to its original form). And it the pressure is decreased in the air around the soda, the soda should go flat faster.

Does chasing air from the soda bottle actually keep the soda from going flat, and most importantly how?

usernumber
  • 467

2 Answers2

-1

My wild guess. According to ideal gas law : $PV=nRT$ in isothermal process if you decrease volume N times, then you need N times less amount of gas to keep same pressure P which was before volume decrease. So in essence, when you squeeze bottle and close it,- carbon dioxide going out to small volume of air quickly restores pre-opening pressure condition of bottle, until it becomes in equilibrium with rest system with no CO2 bubbles coming out. Accordingly, best way to keep the soda from going flat (for longest period and with biggest concentration of $CO_2$) would be to leave no space for carbon gas at all (i.e. so that whole bottle would be filled with carbonated fluid only).

Agnius Vasiliauskas
  • 16,916
-2

I don't know the formula, but I'd be willing to bet that when the system is in equilibrium, there must be a mathematical relationship between the concentration of CO2 in the solution, the temperature of the solution, and the partial pressure of CO2 in the space above the solution.

Squeezing air out of the bottle only makes room for more CO2 to evaporate from the solution and re-inflate the bottle before the equilibrium is reached.

Solomon Slow
  • 17,057