A way-cool clip posted on Reddit shows the strange phenomenon of a "snap freeze."
Poster DifficultBoss shared a short video of a bottle of spring water rapidly freezing, from top to bottom, when shaken after being left outside in cold weather. The science behind this sudden transition has to do with how water changes from liquid to solid.
When it hits its freezing point of 32 degrees Fahrenheit (zero degrees Celsius), water normally starts to crystallize into ice. But this crystallization process requires a home base — a nucleus that water molecules can arrange themselves on. If the water is pure enough, crystallization won't happen, according to the University of Illinois Physics Van outreach program. Liquid water that is below freezing is said to be "supercooled." [Check Out Amazing GIFs of Chemical Reactions]
The snap freeze happens when this delicate, supercooled state is disturbed, as it is in the video when the poster gives the bottle a small shake. The shake likely dislodges a miniscule piece of frost from the inside of the bottle lid, providing that missing nucleation site. The ice crystals then grow on one another in a matter of seconds.
How solid the water freezes depends on the outside temperature, which isn't shared in the Reddit post. According to Physics Van, since water releases 80 calories per gram in heat when it freezes, typical kitchen freezer temperatures (which aren't more than a few degrees below freezing) usually aren't enough to freeze a bottle of water rock solid. The water that is freezing actually gives off enough heat to keep the rest of the water in a liquid state, resulting in slush. However, in cold-enough temperatures, a water bottle could indeed snap freeze quite solidly: Water can be supercooled down to as low as negative 43.6 degrees F (negative 42 degrees C), according to Physics Van.
The liquid-to-solid transition isn't the only time that water behaves strangely. It can happen at water's boiling point, too. Water can become superheated when its temperature goes above 212 degrees F (100 degrees C) without transitioning to a gaseous state. Just as with supercooling, this happens in water pure enough and containers smooth enough not to provide nucleation sites. Just like ice crystals in supercooled water, the bubbles that start the boiling process have nothing to cling to. But superheated liquids can be quite a bit more dangerous than supercooled ones: Instead of turning to ice when moved, they can suddenly erupt into a gas, leading to an explosion of very hot liquid. Microwaving distilled water can cause this sort of eruption — a phenomenon you can watch on YouTube without any danger of second-degree burns.
Original article on Live Science.
