Phenomena

Boiling Water Using Ice Water

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Steve Mould demonstrates a neat thermodynamic trick in this video by using ice water to boil hot water. The key to understanding this is recognizing that the boiling point of water depends both on its temperature and its pressure.

Here’s the set-up (which, to be clear, neither he nor I recommend you try yourself): microwave some water in an open bottle until the water is hot enough to boil. Remove the bottle from the microwave and screw on the lid. At this point, you’ve confined any water vapor coming off the hot water, thereby raising the pressure inside the bottle. Even though it’s still quite hot, the water will stop visibly boiling.

Now pour ice water over the top of the bottle. Because water vapor has a lower heat capacity than liquid water, this will preferentially cool the vapor. As its temperature drops, its pressure will also drop. Liquid water boils at lower temperatures when the pressure is lower. (This is part of why cooking and baking instructions are quite different in Denver than they are in Miami.) When the internal pressure in the bottle drops, the remaining hot water will start to visibly boil. (Image and video credit: S. Mould)

Animation of boiling water using ice water.
One comment
  1. Shiva Meucci

    Hey, thanks for reminding me about the difference between Miami and Denver; now I can remember how disturbing it is that the layer of life sustaining air is such a thin film on this planet that a little drive in a car significantly changes my ability to breathe.

    …if the sun burps in the wrong direction we all just suffocate.

    But yeah, cool effect. 😀

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