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Why does shaking a soda can and opening it make the soda jump out of the can?

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  • $\begingroup$ Soda contains carbonated water, and by shaking it, the carbon dioxide is released which generated the pressure and the soda jumps out. Even when you open the can without shaking, the gas will come out but slowly. $$\ce{H2CO3 (aq)<->H2O (l) + CO2 (\uparrow)}$$ [Not enough information so posted as comment] $\endgroup$
    – Kartik
    Commented Nov 11, 2015 at 5:39
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    $\begingroup$ Add the word "oversaturated", and that would be the complete explanation. $\endgroup$ Commented Nov 11, 2015 at 6:03
  • $\begingroup$ And the nominal oversaturation is possible due to the can being pressurised under CO2 to begin with. $\endgroup$
    – Beerhunter
    Commented Nov 11, 2015 at 7:36

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Soda drinks are carbonated meaning that carbon dioxide is dissolved into it. When carbon dioxide dissolves, the following reaction occurs: $$\ce{CO2(g) + H2O(l)~ \leftrightharpoons ~H2CO3(aq)}$$ As you can see, carbonic acid (a weak acid) is formed. This is responsible for the 'fizziness' of the drink.

Note that this reaction is in equilibrium, meaning that not all of the carbon dioxide dissolves to form carbonic acid, but only a certain percentage of it. Usually, the percentage of carbon dioxide that is dissolved is constant, however this can be changed by doing certain things to the system.

For example, by decreasing the pressure, the equilibrium will shift to the left, meaning that the percentage of carbon dioxide that is dissolved will decrease. This will result in an increase of gaseous carbon dioxide in the bottle. This reason for this is explained by the Le Chatelier's principle. You can also imagine it as a piston pushing the gas into the liquid as shown in the below image. Image (a) is at low pressure while image (b) is at high pressure.

enter image description here

Normally in soda bottles, the pressure inside the bottle is relatively high, to ensure that more carbon dioxide dissolves into the drink. So when you open a soda can you decrease the pressure. This results in more carbon dioxide gas being produced. It is the release of this gas that causes that pfffftt sound.

Now, when you shake the bottle, due to turbulence, small bubbles containing carbon dioxide form. The formation of these small bubbles allows even more carbon dioxide gas to form. So if you shake a soda can and then open it soon after, the soda will jump up quite violently, as there is now a lot of carbon dioxide being released.

However, if you shake a soda can, and then wait a while before opening it, it will most likely just create the normal pfffftt sound. This is because you give the system some time to go back to its original equilibrium position, meaning that some of the carbon dioxide gas will redissolve back into the solution .

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  • $\begingroup$ No worries, I am glad that I could help. $\endgroup$
    – Nanoputian
    Commented Nov 11, 2015 at 10:45
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    $\begingroup$ Well this isn't quite right. In truth $$\ce{CO2_{(g)} <-> CO2_{(aq)} <-> H2CO3_{(aq)}}$$ Most of carbon species in water is dissolved gas not carbonic acid. $\endgroup$
    – MaxW
    Commented Nov 12, 2015 at 18:08
  • $\begingroup$ I think the key here is fluid mechanical: shaking moves the fluid around, reducing the effective pressure, then the carbon dioxide tries to make up for it, per Le Chatelier. $\endgroup$ Commented Dec 23, 2022 at 15:47
  • $\begingroup$ Shaking does not change the pressure It simply distributes small bubbles of CO2 throughout the liquid that all expand more or less together entraining liquid. when the bubble is on the top only gas escapes. try opening the bottle upside down and see what happens. $\endgroup$
    – jimchmst
    Commented Dec 27, 2022 at 1:13
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I was watching a Vertassium episode where Dr. Muller was holding a soda bottle with a pressure gauge atop that registered a rather high pressure. He guaranteed that the bottle was still a long time and equilibrated and asked what would happen to the pressure when the bottle was vigorously shaken. I thought about it and said Nothing. He shook it and the pressure did not change. The reason a shaken soda erupts seems to be the distribution of microgas bubbles thruout the liquid that expand when the pressure is released, not conversion of carbonic acid to CO2 or even CO2 being released from the solution. Champagne seems to require additional research. Maybe by New Years Day that research can be finished.

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Soda or other cool drinks like Coke, Pepsi etc. contain water along with dissolved carbon dioxide (aerated). Since the solubility of carbon dioxide increases with increase in pressure (Henry's law), the Soda is bottled under pressures higher than the atmospheric pressure.

When we open the soda bottles or cans, the pressure drops again to atmospheric pressure and the dissolved carbon dioxide will escape out into the surroundings. It occurs all of sudden so that soda will jump out with fizz. The scenario will be even more worse if we shake the bottle before opening due to thrust created. Remember that soda can be referenced as carbonic acid, H2CO3. For more information see carbonate and bicarbonate chemistry.

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  • $\begingroup$ Explain thrust created! $\endgroup$
    – jimchmst
    Commented Dec 25, 2022 at 3:35

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