Does Shaking a Soda Can Increase Pressure?

[f91jsw]

If you shake an (unopened) soda can or bottle, will the pressure inside increase or stay the same? If it does increase, what is the mechanism? Assumption: the soda has been at constant temperature for a long time.

(please don't answer "of course it increases" just because the soda explodes when you open it after shaking. That's a different issue)

/J

 

[Danger]

My opinion only; I've never really looked into it. Since there's no chemical or thermal change in the contents, the pressure should remain constant. I suppose that the agitation merely disturbs the CO2 out of solution more rapidly than it normally escapes.

 

[jasc15]

(please don't answer "of course it increases" just because the soda explodes when you open it after shaking. That's a different issue)

/J

I don't think you can disregard that statement. The point here, I think, is to explain why the can would explode after shaking, but not if it isn't shaken. obviously the pressure increases when it is shaken, so what causes it? I don't think the CO2 in solution exerts any pressure, but when it is removed from solution, and becomes gaseous, it does exert a pressure.

 

[f91jsw]

obviously the pressure increases when it is shaken, so what causes it?

The explanation for why it explodes is that shaking will cause a lot of microscopic bubbles in the liquid. When you open it these bubbles will want to expand. There is no need for an increase in pressure in this picture which is why it is not "obvious" at all that the pressure would increase.

/J

 

[Cyrus]

If you shake an (unopened) soda can or bottle, will the pressure inside increase or stay the same? If it does increase, what is the mechanism? Assumption: the soda has been at constant temperature for a long time.

(please don't answer "of course it increases" just because the soda explodes when you open it after shaking. That's a different issue)

/J

When you shake the soda you release CO2 gas that was dissolved in the soda and the pressure increases. All you have to do is feel the can when you shake it. It becomes very rigid.

 

[DaveC426913]

When you shake the soda you release CO2 gas that was dissolved in the soda and the pressure increases.

Can you please clarify your use of the term "release" in this context?

 

[Cyrus]

I thought they dissolve C02 into the soda, and it gets released from the liquid when you agitate the soda, and builds up pressure in the can.

When the C02 changes into a gas state, it has a large volume increase, and so the pressure builds up.

No?

 

[DaveC426913]

The question here is, how does the CO2 change from dissolved to gaseous merely from shaking, without any other change.

 

[Cyrus]

Some chemical substances are sensitive to shock and vibrations, maybe this is what is happening?

Help, we are in need of a chemist!

 

[f91jsw]

The question here is, how does the CO2 change from dissolved to gaseous merely from shaking, without any other change.

The first question is, does it really change from dissolved to gaseous? The first thing we have to establish is whether it really does and whether the pressure actually increases.

I just made a little experiment using 4 cans of beer. I shook two of them. Then I tried to feel if there was any difference in how rigid they felt before and after and also comparing with the two cans I didn't shake. I couldn't feel any difference.

/J

 

[brewnog]

Evidence for the pressure increasing; the old designs used to burst if you shook them up enough.

 

[Farsight]

I thought the shaking primarily created and distributed nucleation sites rather than doing all the pressure-increasing there and then. Then when you open it and release a bit of that pressure, all the nucleation sites grow bubbles and push the pressure up enough to expand the contents all over your face.

 

[jasc15]

I just made a little experiment using 4 cans of beer. I shook two of them. Then I tried to feel if there was any difference in how rigid they felt before and after and also comparing with the two cans I didn't shake. I couldn't feel any difference.

/J

Ok, now try this: take a plastic bottle of soda, preferably half full or so. close the cap tightly and squeeze the bottle, it should give fairly easily. now shake it and try to squeeze.

 

[dav2008]

Beer might not be carbonated enough for you to feel the difference.

 

[pervect]

I've stopped drinking soda, but this does suggest an interesting test. Have someone else shake up a plastic bottle. Without knowing which bottle was shaken, see if one can determine which was disturbed by manually testing the rigidity which one was shaken up. (I suppose a purist would insist on a double-blind experiment, but that level of care would probably only be needed if initial results look promising).

This could actually be handy if it works - sometimes a single bottle in a bunch gets disturbed (as in - rolls down the driveway, for instance) and it would be handy to be able to test to identify the disturbed bottle (if one gets it confused witht the other bottles), or to see how safe it is to open yet.

 

[f91jsw]

Ok, now try this: take a plastic bottle of soda, preferably half full or so. close the cap tightly and squeeze the bottle, it should give fairly easily. now shake it and try to squeeze.

Initially of course the pressure will increase, until a new equilibrium is reached, that's trivial. My question was, does the pressure increase after equilibrium has been reached if you shake the bottle?

/J

 

[russ_watters]

Well, then get two bottles, empty half the soda out of both, let them sit for a few hours to get back to equilibrium, then shake one and see if you can feel the difference.

If you really want to get scientific, you could drill a hole in the cap of each and feed a bicycle tire valve stem through it to actually measure the pressure.

 

[f91jsw]

Well, then get two bottles, empty half the soda out of both, let them sit for a few hours to get back to equilibrium, then shake one and see if you can feel the difference.

I think no one is disputing how the experiment would be done. I have done it on unopened cans and I can't feel any difference. I don't see what using half-emptied bottles would add. Since nobody has produced any experimental or theoretical evidence otherwise the preliminary conclusion must be no increase in pressure by shaking, which also theoretically seems plausible.

/J

 

[Cyrus]

But it does gain pressure. Shake up a coke bottle and see for yourself.

 

[GOD__AM]

Drop a 2-liter on hard ground from about 3 foot or so. This will surely make the bottle expand, and you will be able to feel a difference.

 

[f91jsw]

But it does gain pressure. Shake up a coke bottle and see for yourself.

I've tried it on (plastic) Coke bottles now. Still can't feel any difference. Are you sure you can feel a difference or are you just making that assumption?

/J

 

[Cyrus]

Yep, I am sure. Shake the hell out of it. Get a fresh cold 20oz coke or pepsi.

Tell you what, get a *metal* can, and try and put a small dent in it. Then shake the hell out of the can and watch the dent pop back out. Instant proof.

 

[Astronuc]

Certainly the pressure increases when the gas comes out of solution into bubbles, because the gas atoms accumulate in bubbles where there is no intermolecular force binding them (what makes a gas a gas - no or extremely little intermolecular attraction). The surface tension in the liquid provides less restraint on the gas than the intermolecular forces between the gas and liquid molecules, and among the liquid molecules. Consider gas molecules (g) in a volume of water molecules (w)

Before bubble nucleation
w w w w w w w w w w w w
w g w w w g w w w g w w w
w w w w w w w w w w w w
w w w w w w w g w w w w
g w w g w w w w w w w w

After bubble nucleation
w w w w w w w w w w w w
w w w w g g g w w w w w w
w w w w g g g w w w w w w
w w w w w w w w w w w w
w w w w w w w w w w w w

The separation of gas molecules is actually much greater before bubble nucleation.

Why does the gas come out of solution - all it takes is sufficient mechanical energy or a disturbance to 'nucleate' bubbles in what is a supersaturated system. The bubbles then collect more gas atoms by virtue of the fact that the gas atoms are randomly diffusing through the liquid. One might see a few bubbles toward the sides of a polyethylene bottle.

Think of the volume of gas in the liquid. The molecular density of gas is about three orders of magnitude less than water, so there can be a lot of separation between gas atoms in the liquid.

One can certainly feel the increase in pressure as Cyrus and others indicated. A polyethylene bottle will 'feel' much firmer and will slightly expand under tension. Also, if one 'thumps' the bottle, the sound will be different since the resonance of the plastic container under tension is different.

 

[Danger]

Thanks, Astro. It didn't make sense to me until your explanation. My mistake was based upon the assumption (yeah, I know... never assume) that the cans were factory-pressurized specifically in order to keep the gas in solution.

 

[f91jsw]

Why does the gas come out of solution - all it takes is sufficient mechanical energy or a disturbance to 'nucleate' bubbles in what is a supersaturated system. The bubbles then collect more gas atoms by virtue of the fact that the gas atoms are randomly diffusing through the liquid. One might see a few bubbles toward the sides of a polyethylene bottle.

The prerequisite of this whole discussion is equilibrium, i.e., no supersaturated system. So I can't see how your argument can be valid.

/J

 

[beluluk]

Sorry to add up oil in the fire.
One more fact that i know is that the coke can also gets colder when you shake it. Try an unfrozen can of soda.
It comes to me that the shaking could probably do something like when we are stirring a spoon when we are mixing coffe with milk or sugar. I presume that shaking is forcing some chemical reaction, it is like when we are shaking a bottle with water and vegetable oil in it.
I don't know for sure, but soda is "carbonated" water, not "carbondioxided water". Probably the carbon in the soda mixed with the oxygen in the free air inside the can/bottle, and produced a gas(freeing up some energy so it becomes cooler), namely carbondioxide.

I'm not so sure about this. So..., tell me whether I'm right or wrong.

 

[Cyrus]

The prerequisite of this whole discussion is equilibrium, i.e., no supersaturated system. So I can't see how your argument can be valid.

/J

I don't understand your statement. Perhap's you need to restate your question more clearly. It seems that you got an answer to your first question in the origional post. You have now somehow modified your question with this whole equilibrium issue, and I can't figure out what it is you are trying to get at anymore.

 

[Bystander]

"THE BLIND MEN AND THE ELEPHANT"

http://www.constitution.org/col/blind_men.htm
http://www.cs.princeton.edu/~rywang/berkeley/258/parable.html

Decisions. Decisions. Decisions. Hit the "Report Bad Post" button and ask the mods to do something about the hand-waving and speculation in this thread, or, do a little cataract surgery?

If you shake an (unopened) soda can or bottle, will the pressure inside increase or stay the same? If it does increase, what is the mechanism? Assumption: the soda has been at constant temperature for a long time.(snip)

A two phase closed system, liquid (aqueous solution of proprietary components) and gas (carbon dioxide plus water vapor plus other gases and volatiles), at thermodynamic equilibrium, and in thermal equilibrium with a constant temperature environment (room T), in a sealed, approximately constant volume container, is subjected to a series of accelerations sufficient to cause turbulent flow and impacts of liquid with the container walls. Does the pressure within the system post-shaking differ from the equilibrium pressure prior to shaking? What are the mechanisms producing the change, if any change is noted? Those the questions?

Answers: 1) yes, the effect can be observed in water equilibrated with air at one atmosphere (not as pronounced or long-lived); 2) the mechanism depends upon production of low pressure volume elements within the liquid phase by liquid shearing, cavitation (acceleration of the container away from the liquid-container interface), acoustic rarefaction ("Conn, sonar, we are cavitating," Jonesy to Mancuso, The Hunt for Red October, Tom Clancy, 1984), and the differences in the kinetics of solution and exsolution of gases. Rate of solution is a function of liquid-vapor interface area (nearly constant), and the diffusion coefficient for dissolved gases, and their dissociation products; the rate of exsolution is dependent upon the volume of liquid that can be subjected to pressures lower than the original equilibrium pressure.

 

[Astronuc]

The prerequisite of this whole discussion is equilibrium, i.e., no supersaturated system. So I can't see how your argument can be valid.

A supersatured system is in equilibrium, until there is a disturbance which 'disturbs' the equilibrium.

A gas like CO₂ under pressure will dissolve in a liquid. I bought two bottles of carbonated beverage yesterday. Both were under pressure. When opened the pressure drops (equilibrium changes) and the CO₂ formed bubbles in the liquid. The bubbles are also bouyant and try to rise - that is why they force liquid out of the bottle if it is opened to rapidly.

Divers also have a problem that nitrogen gas dissolves under pressure. That is why divers have to come up slowly so that the nitrogen has time to come out of solution in the blood stream and tissue, otherwise nitrogen bubbles form in the tissue and circulatory system leading rather painful and potentially fatal condition. That is one reason deep divers use He/oxygen or Ar/oxygen mix.

 

[Bystander]

A supersatured system is in equilibrium, (snip)

Reeaaalllllllllyyyyyy? A supersaturated solution is in a metastable state, but it is NOT in equilibrium. The changes in state it undergoes when sufficiently disturbed are NOT reversible. The soda container will return to its original state of equilibrium after shaking.

 

[Astronuc]

Yes, really!

For example,

Carbonated beverages are supersaturated solutions of CO2.

http://www.Newton.dep.anl.gov/askasci/gen01/gen01191.htm

Thermodynamic equilibrium, when internal processes of a system cause no overall change in temperature or pressure. Wikipedia - http://en.wikipedia.org/wiki/Equilibrium

I would prefer a more reliable source than Wikipedia, but that'll have to suffice for now.

A 'sealed' bottle of carbonated beverage - left to itself - is in equilibrium. Shack it (an external influence) can release some gas - pressure increase. Then over time the CO₂ will diffuse/dissolve back into the liquid and internal pressure decreases to a new equilibrium.

I did not quantify the degree of supersaturation.

 

[f91jsw]

Yes, really!

For example,
http://www.Newton.dep.anl.gov/askasci/gen01/gen01191.htm

The web page you quote implies that carbonated beverages are supersaturated solutions of CO2 at atmospheric pressure, which is correct. At the elevated pressure in the unopened can I would argue that it is not supersatured. I guess it depends on how you define "supersaturated." Obviously a supersaturated system is not in its lowest energy state. After a long time the unopened soda will be in its lowest state (more or less) and thus it cannot be supersaturated.

A 'sealed' bottle of carbonated beverage - left to itself - is in equilibrium. Shack it (an external influence) can release some gas - pressure increase. Then over time the CO₂ will diffuse/dissolve back into the liquid and internal pressure decreases to a new equilibrium.

This is the core question of this discussion - is the process you describe above physical or unphysical? Intuitively I would say it's unphysical. Can you refer to the theory which explains how the equilibrium would change by shaking?

/J

 

[Bystander]

Yes, really!

For example,
http://www.Newton.dep.anl.gov/askasci/gen01/gen01191.htm
(snip)

f91jsw has read your link correctly; an open container of carbonated beverage exposed to the atmosphere is "supersaturated" with respect to the equilibrium state of the same beverage with the atmosphere. That is, the concentration dissolved in the beverage, 0.1m to 0.2m, is greater than the 15-20 micromolality at equilibrium.

In a sealed container, closed system, the equilibrium state is for a carbon dioxide activity of around 150-200 kPa (I've never gauged it). It is NOT supersaturated. The definition of the system is that the container is sealed, closed, not open to atmosphere, and the OP's question has to do with the response of the system to mechanical agitation.

 

[f91jsw]

Entropy argument: let's assume we have a situation where we have a sealed container where one part of the volume is occupied by pure water and the remaining part is occupied by pure CO2 at a certain pressure. If we now wait for a sufficiently long time the system will reach an equilibrium state where some of the CO2 will be dissolved in the water. The entropy has increased and we have reached thermodynamic equilibrium.

Now, what happens if we shake the system? According to some posters here some of the CO2 will return to gaseous state and the pressure will increase. I.e., the entropy will decrease again. How could it be possible that a random process such as shaking would lower the entropy of the system?

/J

 

[beluluk]

Now, what happens if we shake the system? According to some posters here some of the CO2 will return to gaseous state and the pressure will increase. I.e., the entropy will decrease again. How could it be possible that a random process such as shaking would lower the entropy of the system?
/J

I don't understand entropy very much , but i believe it's similar to shaking a bottle with water and oil in it. The water and the oil will mix temporarily. After a short period, the water will go down and the oil will go up. I've read nothing about its explanation, but i suspect gravity responsible for this.:tongue2: