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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 Nov 11 '15 at 5:39
  • $\begingroup$ Add the word "oversaturated", and that would be the complete explanation. $\endgroup$ – Ivan Neretin Nov 11 '15 at 6:03
  • $\begingroup$ And the nominal oversaturation is possible due to the can being pressurised under CO2 to begin with. $\endgroup$ – Beerhunter Nov 11 '15 at 7:36
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Soda drinks are carbonated meaning that carbon dioxide is dissolve 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. It this which is responsible for the 'fizziness' of the drink.

Note that this reaction is in equilibrium, meaning that not all of the carbon dioxide dissolve to form carbonic acid, but only a certain percentage actually dissolves. 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 to 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 allow even more carbon dioxide gas to form. So if you were to 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 were to shake a soda can and then wait a while before opening it, it 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 Nov 11 '15 at 10:45
  • $\begingroup$ 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 Nov 12 '15 at 18:08
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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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