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Classical Mechanics Level 2

Why do the bubbles from a freshly opened bottle of champagne grow as they rise to the surface?

Friction with the champagne heats the gas inside the bubble Fluid pressure falls as the bubble rises in the glass The bubble continues to accumulate dissolved gas molecules as it moves through the champagne The bubble does expansive work on the champagne as it loses potential energy

1 solution

Michael Mendrin
Nov 6, 2015

The solubility of a gas in a liquid increases with pressure, so when the pressure drops, then the dissolved gas ( $\ce{CO2}$ in champagne, e.g.) wants to escape from the supersaturated liquid and into either free space or more gas. Once a tiny bubble forms via any nucleation process, which could happen anywhere, then suddenly that's the go-to place for dissolved gas to escape to. As the bubbles rise, they expand as they attract riders like how trains attract riders that jump aboard during motion.

As the bubble of gas rises, the pressure drops and the volume increases. The best answer is the last one !! This is why a scuba diver should never hold his breath as he ascends. The expanding air in his lungs will rupture them and cause an embolism. Any more gas wanting to come out of solution will create MORE bubbles. In the scuba diver's situation this relates to causing the bends. The answer is incorrect for this question - it should be changed.

Bob Kadylo - 5 years, 7 months ago

After investigating further, I admit the infusion of more gas into the bubble as it rises, causing the expansion, is happening! However, the question is - which effect is the dominant one? Also, how much gas is dissolved in the liquid at the time? Is the champagne almost flat or was the bottle just opened? This problem is VERY complex - and at least should have a few initial assumptions spelled out !!!

Bob Kadylo - 5 years, 7 months ago

The bubbles do expand because of less hydraulic pressure as they rise, but the difference is quite small. If those tiny bubbles started at the bottom of a 30 foot deep lake, then by the time they reach the surface, they'd only have expanded twice in size. 14 psi at surface, 28 psi at the bottom. (A square-inch column of water exerts about $0.43$ pounds per foot depth, plus the 14 psi atmospheric pressure.) So, since the champagne bubbles are obviously expanding much faster than that, there has to be another reason.

We can assume that the champagne is already supersaturated with $CO2$ when opened, which is the reason why the cork wants to fly with a bang.

Michael Mendrin - 5 years, 7 months ago

Thanks for reaching out Bob! I've attempted to modify the problem statement so that there are implications that it's a freshly opened bottle of champagne. Hopefully this will emphasize the supersaturation of $CO2$ and remove some ambiguity.

Andrew Ellinor - 5 years, 7 months ago

Yeahh u r right sir!!

Ishan Das - 5 years, 7 months ago

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