NEW ZEALAND PHYSICS TEACHERS' RESOURCE BANK

Cooling by Boiling

Poster frame from video: In most browsers, Click on image to play OR Right-click on image and "save target as" to your computer, then play in QuickTime, Windows Media Player, or another player.

Pumping causes boiling that results in cooling the water

Temperature of the water decreases as boiling proceeds

Abstract

Water in a vacuum jar boils even though it is below room temperature. As the pumping proceeds, the water cools.

Portable Yes
Principles Illustrated

The molecules of water in the liquid have varying amounts of energy. The most energetic are able to leave the liquid and enter the vapour. As these are pumped away, the average energy of the molecules left behind in the liquid decreases. This is seen as a reduction in the temperature of the liquid.

NCEA & Science Curriculum
Teacher Guide
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Video
Instructions

Cold Trap || Cold Trap After Experiment

Note: This one works well in a large lecture theatre with a video camera pointed into the vacuum jar and connected to a data projector.

Note: This demonstration can wreck your vacuum pump by contaminating the oil with water. Use an old one if possible and change the oil after finishing the demonstration. Be sure the cold trap is in place and cold (use Liquid Nitrogen) or you may ruin the pump.

Diagram

 
Safety

 

Be sure to use a sturdy vacuum jar. Also, wear goggles when using the syringe as the top can pop off if the handle is released suddenly.

Individual teachers are responsible for safety in their own classes. Even familiar demonstrations should be practised and safety-checked by individual teachers before they are used in a classroom.
Related Resources

You can do something quite similar with a syringe full of warm water. Pull the syringe back hard and watch the water boil.

Example Data
Example Data is available upon request. Please contact us.
Credits

This teaching resource was developed by the Te Reo Māori Physics Project with support from

 

  • This resource was developed by the Te Reo Māori Physics Project.
  • The New Zealand map shown on the poster frame above is used with permission from www.nz.com.
  • This teaching resource was developed in collaboration with Mabel Stewart, a New Zealand Science, Mathematics and Technology Teacher Fellow, 2008, hosted by Victoria University School of Chemical and Physical Sciences. See NZSMT Teacher Fellowships for more information about the Teacher Fellow Programme.

Copyright

Copyright and fair use statement