Q & A: Melting ice really really fast

Q:
Which is the quickest way to melt ice?
- Alyssa (age 12)
Harwich, MA USA
A:
Hi Alyssa,

Well, you had to ask! Melting ice involves transferring heat energy to the ice -- 80 calories per gram, to be specific. If the pressure stays at one atmosphere, then ice at zero degrees Celsius will turn into water at 0 degrees Celsius once the heat is transferred.

The problem now is to find the quickest way to get heat energy into the ice. The quickest ways are also very very dangerous and I do not recommend doing them. Transferring large amounts of heat energy in a short amount of time has the usually unpleasant side effect of getting heat energy all over the place where you might not want it (including on yourself).

The very quickest way I can think of to melt a reasonable amount of ice (less than a kilogram, for instance), is to explode a bomb next to it. The bigger the explosion, the faster your ice will melt. In fact, the ice will vaporize in a tiny fraction of a second if your bomb is big enough. I do not recommend doing this, however -- you could get hurt or you could be put in jail or both.

You could use a blowtorch. Again, this is UNSAFE, but at least it is more legal. If you are more patient, you can put the ice in a microwave oven and turn it on high. You can see our answers on microwave ovens to find out how they work, particularly with water molecules. A gas or electric range, with the ice in a pot, also will melt the ice rapidly. You can speed this up quite a bit by adding hot water to the pot. In fact, you may not even need the stove. Adding salt to the hot water will speed up the process more, because the ice will melt at a lower temperature, and heat flows faster between things with temperatures which are more different.

One way to increase the speed with which you melt the ice is to increase its surface area, so heat can be absorbed in more places. Crushing the ice up into small bits will speed up the melting rate.

A safe, easy, rapid way to melt ice is to chop it up into little bits and to then pour boiling saltwater over it.

If you have more ice than you can put in a pot, you can let nature do the job. Let the sun shine on it, or pour some salt on it. As I write this, Lake Superior is frozen over -- it is expected to melt in April sometime. The heat energy will certainly have to come from the Sun to melt it (and some from the heat of the Earth).

You can also melt small amounts of ice rapidly by squeezing on it. Ice takes up more space per gram than water at 0 Celsius, and so it prefers to be water when squeezed really hard. Underneath the blades of an ice skater's skate, a tiny amount of the ice will actually turn very rapidly into a thin layer of water and then back into ice again (it works best when the ice is just under the melting temperature).

Tom

(published on 10/22/2007)