Han wrote in
:

snip
Actually, superheating is a wellknown phenomenon. For water to boil,
it has to go to vapor phase (steam). That usually (in a pan on a fire
of some kind) at very hot places on the pan's surface. That's when
the water is starting to "sing". In a MW there is no such hot surface
and boiling has to start somewhere. This is then usually on a
floating speck of dust. The MW energy has heated the water in the
meantime to higher than the boiling temperature, so when a teensy
"boil" starts, suddenly this is the seed for much more water to become
steam. Steam is also much, muc more voluminous than water, hence the
force of the boiling water and steam.

When a chem student having to heat solvents on a heated water bath, it
was official policy to add "boiling stones" to the containers in order
to have a controlled boiling, rather than a little explosion. But
that is another story ...

Oh, yeah. 1 mole of water is 18 grams, just over half an ounce.
Visualize that volume. At "normal" conditions (0degrees C, 1
atmosphere pressure), the volume of an ideal gas is 22.4 liters.
Since pV=RT, that volume would be 373/273 times as much at 100 degree
C (boiling), or about 31 L, or close to 8 gallons. Visualize 18
milliliters expanding to 31 liters, roughly 2000 fold. That's the
power of steam.

That explains why you eed be careful pulling the Saran wrap off of a
microwaved food container. Less than 4 tablespoons of water will
convert to 8 gallons of steam when overheated to boiling.


Hope I got the facts right

--
Best regards
Han
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