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by Anonymous on March 20th, 2006
Another answer posted here is incorrect. The formula given therein, “(P1*V1)/T1 = (P2*V2)/T2” describes the behavior of a gas with regard to the relationship between pressure, volume, and temperature. If soda really followed that formula as it froze, it would shrink as the temperature was reduced.
In fact, most substances do shrink somewhat, and become more dense, as they get colder; and they expand, and become less dense, as they get hotter, but it is only within the gaseous state that this happens in the simple and consistent manner described by that formula. Especially across the transistion between solid and liqid, and again across the transition between liquid and gas, the degree of expansion or contraction can vary greatly from one substance to another.
Water has an unusual characteristic; in its solid form, it is less dense than in its liquid form. Thus, as it freezes, it expands slightly. This is why ice floats to the top of liquid water, rather than sinking to the bottom. With most other substances, if you were to put a solid piece of that substance into a container of that same substance melted into a liquid, the solid would sink to the bottom.
This, also, is why a container of a water-based liquid (such as soda) might rupture when frozen. As the water freezes, it expands, taking up more volume, and if the container can't contain that increased volume, it bursts.
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Comments
I knew the gas law did not explain this, thank you
by PhilDoc on March 20th, 2006
Well put!
by Astaroth on March 24th, 2006
Great Answer! If water didn't expand as it freezes and float on water all the fish in lakes and ponds would die.
by Nizard on April 5th, 2006
Expansion with heating and contraction with cooling is a property shared by most matter in most states. The reason things like water (water is not the only one) expand when changing from the liquid to crystalline state because the crystal structure takes up more room than the freely flowing molecules (thanks Hydrogen Bonding!). In fact, there are many different forms of ice. Not all solid/glass forms of water are less dense than the liquid form. It just so happens that at around 1 atm (pressure of earth's atmosphere at sea level) that crystal structure is most stable.
http://ergodic.ugr.es/termo/lecciones/phase.gif
That is a phase diagram of water. 1 atm is roughly equal to 10^6 Pascals. As you can see, it needs to reach a pressure two orders of magnitude (100 times higher) than 1 atm in order to freeze into a different crystal structure. If I recall correctly, a soda can's failure point is generally around 10 atm (140 psi). The can would have to hold 10 times more pressure for it to freeze without rupturing from the ice expansion alone.
That being said, dont discount the CO2 from the mess it will make. If it were a can of water, I hypothesize that the liquid would almost instantly turn to a brick of ice (maybe some splattering) once the aluminum ruptured. As liquid temperature lowers, gas solubility goes up. This means that as the can is cooling more and more of the CO2 the can was packed under is being allowed in solution. Also, as pressure is directly correlated to gas solubility. Once the can ruptures pressure is removed (reducing CO2 solubility) and the liquid begins to form ice. The solubility changes dramatically (CO2 leaves the solution) and CO2 contributes to the classic splattered slushie we are all familiar with.
And just for giggles I'd like to add that PV/T and anything derived from the ideal gas law was taught largely for the conceptual value. Real chemical and engineering formulas must be used for these sorts of problems because even the Nobel gasses aren't 100% ideal. Real molecules have attractive and repulsive forces and collisions are not always 100% elastic.
by Chris_F6241 on July 21st, 2011