The Collapsing Soda Can

This experiment demonstrates Boyles' Law, the relationship between pressure and volume of a gas;:

PV = a constant

ie, if the pressure goes up, the volume goes down and visa versa. If we boil a small amount of water in an aluminium soda can, it will change from a liquid into a gas. A gas occupies much more space than the liquid which gave rise to it. Since a mole of any gas occupies 22.4 l, then 18 cm3 (1 mole) of water when boiled will occupy 22.4 l, enough to fill 11 two litre bottles with some to spare. As the water turns into a gas, it displaces all the air from the inside of the can, so the can is full of water vapour (and some boiling water). If you then invert the can and immerse it in a bowl of cold water, it collapses as if squeezed by an invisible fist - but why?...

To read more click here to download Dr Hal's fact sheet on The Collapsing Soda Can (900kb pdf file)