Hi Brett,
Dry ice is the common name for solid CO2. The temperature of dry
ice is about -78.5 C, and the water you used in your experiment was
probably somewhere around normal room temperature (25 C). The water is
very warm relative to the dry ice so the solid CO2 begins to "melt,"
but unlike water, which changes from a solid to a liquid before turning
into a gas, CO2 changes directly from a solid to a gas at normal
atmospheric pressure. This process is known as sublimation.
As the dry ice sublimes, the pressure inside the bottle increases
because gases take up more space than solids. At some point, the bottle
is no longer able to withstand the pressure that has built up inside,
and it bursts. The loud popping sound is caused by the high pressure
air that was previously inside the bottle suddenly pushing on the
normal pressure air around it, creating a pressure wave that is
detected by your ears and interpreted as sound. (This is different from
a sonic boom, which is caused by objects moving faster than the speed
of sound.)
By the way, blowing up bottles this way is kind of dangerous...please be very careful!
Thanks for your question!
(published on 10/22/2007)
