Guru Kate: Ka Boom! H2O blast

Why can it be dangerous to boil water in the microwave?

MythBusters has showed us that putting water in the microwave and then sticking a fork in it makes a pretty awesome explosion. But if you don’t have sweet safety glasses and are protected head-to-foot, it can scald you.

This happens because the water gets superheated. Undisturbed by you not testing its heat every 30 seconds (maybe this is just me and my radical impatience), it stores up a whole bunch of energy, but doesn’t get that extra kick it needs to enter gas phase.

Kind of like a kick-start, but one that can radically change the look on your face. Literally.

So it lays in wait. Waiting, waiting, waiting. Until you open the magical microwave door and disturb the arrangement of the water molecules.

“Oh snap,” the mug of 300°F water says, “it’s my time to shine.”

This disturbance creates a cascade reaction where each H2O molecule shoots into the gas phase and releases a whole bunch of energy in the process. And where will all that energy go? It is contained on three sides by the microwave…but that fourth side is a doozy.

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There are many factors that play into the likelihood of this occurring: how scratched the mug is, how long the liquid has been sitting undisturbed for, and if the drink is mixed thoroughly before heating.

If the mug is scratched, there will more likely be gases trapped within the mug—pre-disturbing the liquid and preventing Blister Party 2012. Liquids that have been sitting for a while (like if you left that tea in the microwave and need to re-heat it) can settle out all of their air bubbles and be ripe for the superheating.

However, not all super-charging of chemicals is scary. Superheated water is used quite often in Alaska in pressure-cookers to make home-canned goods.

Super-charging also happens daily in malls across America, in a really hot way. Booths set up to sell hair accessories, cell phone gadgets and gym memberships are now accompanied by booths that sell supercoolers (basically the mirror opposite of a superheater).

The merchants tote them as heating pads. Instead of superheating water, they supercool sodium acetate. And instead of superheating it from a liquid to a gas, sodium acetate supercools from a solid to a liquid.

The grand thing about sodium acetate is that it can be harnessed in a small plastic package. When it is supercooled, it’s fully charged with energy. The plastic packages look like they’re filled with a clear gel. It is actually liquid sodium acetate that is ready to rush back to its solid form and release a whole bunch of heat energy on its way.

Neat stuff. And it all lets you keep your eyebrows on your face.