When boiling water is thrown into extremely cold air, it transforms into a cloud of ice crystals or a burst of snow. This visual, often seen on social media, demonstrates principles of physics. It highlights water’s behavior under severe temperature differences.
The Science of Instant Ice
The transformation of boiling water in frigid air is rooted in several scientific principles. Boiling water contains energetic molecules that evaporate more rapidly than colder water, creating a volume of hot vapor.
When dispersed, the boiling water breaks into tiny droplets, increasing its surface area. This surface area allows for rapid heat transfer to the frigid air.
As these hot water droplets encounter the cold air, they do not instantly freeze. Rapid cooling causes the water vapor to condense into liquid droplets, forming a visible cloud. These liquid droplets rapidly shed their latent heat. Latent heat is the energy released or absorbed during a phase change. Once this heat is released, the tiny droplets undergo an instantaneous phase change, turning into ice crystals or fine snow.
Water can also undergo supercooling, remaining liquid below its normal freezing point of 0°C. This can occur in water droplets without nucleation sites. Once a nucleation event occurs, these supercooled droplets freeze quickly. While some might associate this phenomenon with the Mpemba effect, the boiling water trick primarily relies on rapid evaporation and maximized surface area.
Ideal Conditions and Safety
For the best effect, the air temperature needs to be cold, -20°C (-4°F) or lower. Some sources suggest -30°F (-34°C) or colder. If the temperature is not sufficiently low, the water may fall as liquid or create a less impressive mist.
Beyond temperature, other environmental factors play a role. Low humidity, or dry air, is beneficial because cold air holds little moisture, promoting rapid condensation and freezing when hot water is introduced. Minimal wind is also important for safety and to observe the full effect, as strong winds can dissipate the cloud or blow the boiling water back towards the person.
Safety is important when attempting this experiment. Boiling water can cause severe burns if the water does not fully vaporize or if wind shifts the trajectory. Injuries, including first- and second-degree burns, have been reported. Throw the water away from yourself and others, wear protective gear like gloves and eye protection, and ensure no one is standing downwind. Children are particularly vulnerable to severe burns due to their thinner skin.