View Full Version : Shaken Soda--A week later
11-03-2009, 01:11 AM
Last week, I bought several sodas and put them in my trunk. Some had fallen out of the bags. So, I put them in refrigerator and drink the first bottle. Nothing happens, I finish it and open the second bottle..and it sprays all over the place. I assume it was from being loose in the trunk, but that was 6 days ago. Shouldn't a shaken bottle have "calm down" by this time?
11-03-2009, 02:38 PM
This question has a couple really easy answers, and a more complicated one.
Easy answer #1: Someone shook up the bottle when you weren't looking. Of course this is more likely if you have kids in the house.
Easy answer #2: Bottle #2 was a random manufacturing defect and it had nothing to do with the shaking at all. I've noticed that some bottles will spray at me with no prior shaking, whereas most bottles do not and are easily drinkable. I always found that this was most common withVintage brand seltzer water when I was a kid.
The complicated answer: It has to do with the solubility of the carbon dioxide dissolved in the soda. As most people know, the easiest way to let a soda go flat or have it spray all over you is to let it get hot. Unlike solid-liquid mixtures in which solubility improves with higher temperatures, liquid-gas solubility improves with lower temperatures. This also applies to the shaking. Agitating a solid-liquid mixture improves its solubility, but agitating a gas-liquid mixture will lower its solubility. Combine the high temperature with agitation and you surely have the conditions for explosive soda.
As for why the soda will not "calm down" and be as well mixed as before has to do with one of we chemical engineers' favorite properties, fugacity, literally meaning "tendency to flee or escape." You can read about this property in wikipedia if you like: http://en.wikipedia.org/wiki/Fugacity
Fugacity is a measure of chemical potential and can also be referred to as "Gibbs Free Energy in disguise." At a fixed temperature and pressure, a homogeneous substance will have a different fugacity for each phase. The phase with the lowest fugacity will be the most favorable, and will have the lowest Gibbs free energy. Substances always favor the lowest energy state.
Carbon dioxide has a lower fugacity in the gas phase, so it "wants" to be a gas, not dissolved in the soda. When the can was agitated in the trunk and the carbon dioxide came out of solution, it moved to a more favorable energy state, and thus nature dictated it should stay there. This was manifested by a pressure increase in the can as the carbon dioxide moved from the liquid phase back to the gas phase.
As other chemists/engineers reading this know, there are other factors involved, such as the carbon dioxide being in a metastable equilibrium with the soda at the specific temperature and pressure, which is disturbed by agitation.
Don't worry if you don't understand Fugacity. Most of us refuse to ever use it. The creator of fugacity, G.N. Lewis, killed himself.
11-03-2009, 02:49 PM
...You can read about this property in wikipedia if you like: http://en.wikipedia.org/wiki/Fugacity
...Don't worry if you don't understand Fugacity. Most of us refuse to ever use it. The creator of fugacity, G.N. Lewis, killed himself.
-LeidenfrostReading the linked page reminds me of why I switched from chemical engineering to environmental engineering.
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