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Name: Joe B.
Status: educator
Age: 30s
Location: N/A
Country: N/A
Date: 1/10/2004


Question:
Why does pop explode when it is shaken? When you open the pop not shaken it just makes a fizz sound as the pressure is released. When the pop is shaken no additional pressure is created from outside the can yet the contents will explode out when opened.


Replies:
Joe,

It is all a matter of a gas/liquid solubility equilibrium. When the can of pop is sitting undisturbed, most of the gaseous carbon dioxide "fizz" is dissolved in the liquid. Shaking the can creates bubbles in the liquid that come from the headspace in the can. These bubbles provide nucleation sites in which soluble carbon dioxide can escape from its dissolved state. In essence, the gas/liquid equilibrium is disturbed when the can is shaken. As a result, the carbon dioxide moves from a soluble condition to a gaseous condition in the headspace of the can. When the can is suddenly opened, much of the remaining dissolved gas comes out of solution in a gush. Thus, the mess.

If the can is shaken, but not immediately opened, in time the equilibrium will re-establish itself and the can will not erupt when opened. It will behave just as an unshaken can would if it were to be opened.

Regards,
ProfHoff 774


When a soda is bottled, it is bottled under a pressure of CO2 that exceeds the solubility of CO2 in the rest of the formula (mostly water). When the can is opened without shaking and without other seeds for the dissolved CO2 to form gas the soda slowly loses CO2 until the solubility of CO2 is achieved. When the unopened can is shaken, the supersaturated solution evolves its CO2 with the result that the pressure of CO2 is significantly greater than the normal pressure would be -- hence the "explosive" evolution of CO2 gas. A similar thing happens if you freeze the soda because CO2 is not very soluble in ice.

Vince Calder


Joe B.,

There are three main ingredients in soda pop: water, syrup and carbon dioxide gas. The carbon dioxide gas is responsible for the fizz.

When the ingredients are combined, the carbon dioxide gas, syrup and water form a solution. The ingredients are mixed in a container and the empty space at the top of the container is filled with carbon dioxide gas. The bottle or can is then sealed. The carbon dioxide at the top of the container is under pressure and prevents any of the dissolved carbon dioxide from escaping from the solution.

When the bottle is opened, a familiar hiss is heard and the carbon dioxide gas in the top of the bottle is released. The dissolved carbon dioxide can now escape from the solution; the result is the familiar bubbling carbonated drink.

When you vigorously shake a can or bottle of soda, this gives the carbon dioxide gas more kinetic energy (motion) and causes the pop to spray or as you say "explode" from the bottle. I hope that this helps.

Sincerely,

Bob Trach



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