# Chemistry of Heat Pack

**URL:** <https://boards.straightdope.com/t/chemistry-of-heat-pack/47184>\
**Category:** Factual Questions\
**Created:** [December 25, 2000, 7:34pm UTC](https://boards.straightdope.com/t/chemistry-of-heat-pack/47184 "2000-12-25T19:34:08Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Mooney252](https://avatars.discourse-cdn.com/v4/letter/m/7c8e57/32.png) [@Mooney252](https://boards.straightdope.com/u/Mooney252)\
**Post date:** [December 25, 2000, 7:34pm UTC](https://boards.straightdope.com/t/chemistry-of-heat-pack/47184/1 "2000-12-25T19:34:08Z")

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For Christmas, we received a hand-sized plastic pouch called a Zap Pac. It’s a clear liquid in a plastic pouch. When you click a metal disk in the liquid, it turns cloudy, releases heat (about 115 degrees F) and eventually solidifies. You then return it to the original state by boiling it in water for a few minutes.

The questions:  
– what’s the chemistry?  
– how does clicking the little metal disc act as a catalyst?

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**Author:** ![Squee](https://avatars.discourse-cdn.com/v4/letter/s/ba9def/32.png) [@Squee](https://boards.straightdope.com/u/Squee)\
**Post date:** [December 25, 2000, 7:45pm UTC](https://boards.straightdope.com/t/chemistry-of-heat-pack/47184/2 "2000-12-25T19:45:25Z")

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Here is an explanation from [How Stuff Works](http://www.howstuffworks.com/question290.htm).

I love that site!