Hello,
I sent a message on this yesterday, but it got lost (I am in Australia due to work, maybe my message couldn't find the way from here or the jetlag is hurting me more than I thought...).

Just my 0.02 on boiling, distilled water and explosions (still cannot tame the nerd inside).

Linda Pahl is right and Judith Hyman is right, too. The word "boiling" refers to both phenomenon: 

a) the phase change that water will undergo at 100C (212F) and 
b) the phenomenon you observe when a wall is heated and bubbles are produced on the wall, detach and rise through the water. 

This is a heat transfer regime and it is known as "nucleate boiling" because is needs nucleation sites (imperfections on the wall or solutes in the water) to occur.

Now, about the sudden release of energy when superheated liquid water (i.e., liquid water above 100C, where water and vapor coexist in equilibrium at atmospheric pressure) is disturbed. This is called "explosion". More precisely, it is one form of vapor explosion. It is  a great thing they managed to do it on TV. We used to do it in a senior lab course.

There are many wonderful things you can do with heat and water. Try and pour a very small amount of water over a heated surface, you'll see how the droplets "dance around" on the surface (known as Leidenfrost phenomenon). Also heat up water in a very smooth stainless steel pan and see tiny bubble columns form on the very few imperfections at the bottom of the pan. You can also heat up water close to the boiling point and then drop salt in it, and watch tiny bubbles form until the salt dissolves. Then it will take longer for the water to boil because the salt water has a higher boiling point.

And it still amazes me to see the things we can do with liquid gases at room temperature!!

Veronica (who did her PhD in two-phase flow dynamics and likes to be part of the town's science exhibits for school kids)

Veronica Garea
Grupo de Apoyo a la Lactancia Materna de Bariloche
IBFAN Bariloche - LLL Argentina

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