Shaking Soda Cans
Name: Joe B.
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.
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.
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
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
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.
Click here to return to the Chemistry Archives
Update: June 2012