At normal atmospheric pressure, water freezes at zero degrees Celsius and boils at 100 degrees. It is to be noted that the freezing and boiling points of water are how we define the Celsius temperature system. But as always there are some exceptions and as it turns out water doesn’t always freeze at zero degree Celsius. At some conditions we can put a bottle of water in the freezer for hours and it will remain liquid unless we do something.
Here liquids are subjected to a special state called super cooling and it is the state where liquid doesn’t solidify even if it is below the freezing point. Liquids needs something become solid at a certain temperature because there is a process which involves the lineup of molecules. All states of matter solid, liquid, or gas at constant pressure depends on its energy or heat. In a gas, molecules are warmer, and are higher in energy. They move a lot, fly everywhere and collide with each other often. But in a liquid, molecules don’t have as much energy as compared to gas and move around slow enough to form a bonds between them, keeping them close together. At lower temperatures, where molecules have the least amount of energy, they forma solid. They’re still vibrating a bit, but at this point the bonds between them keep the molecules rigidly in place.
In order to freeze water, it should have low energy meaning it should be cold and it should form intermolecular bonds holding it as a solid. To make this bond water has to form a nucleus around which the cool water will for ice eventually. This point is called nucleation site it is the place where structure of ice crystal begins to form. This then allows other water molecules around it to form bonds eventually expanding to make one solid piece of ice. This nucleation sites needs to be created and this creation of nucleation is generally helped by impurities in water. This impurities might be a mineral present in water. Nucleation site can also be created by disturbing the super cooled liquid like shaking. As the very cold water moves around cool molecules will and start the process of turning into ice. So to create super cool water, you have to keep impurities and movement as far as possible.
How to supercool water
To make super cool water you need a freezer and a bottle of standard drugstore-brand purified water. Mineral water is useless as it contains things that will act as a nucleation sites. Keep your bottle of water in the freezer. Keep it in the freezer for about two and a half hours and make sure that you don’t open the freezer because we want gradual cooling and opening the freezer might disturb and gradual cooling process. If everything went well, you will have a supercooled below-freezing liquid water. If you slam this bottle of supercooled water against the table, you will create a nucleation site, and you can actually see the ice crystal form almost instantly. Which is SUPER COOL!