Science, Tech, Math › Science Make a Cold Pack from Hot Ice Cold Pack from Sodium Acetate Share Flipboard Email Print A cold pack results from an endothermic chemical reaction. Matt Meadows, Getty Images Science Chemistry Projects & Experiments Basics Chemical Laws Molecules Periodic Table Scientific Method Biochemistry Physical Chemistry Medical Chemistry Chemistry In Everyday Life Famous Chemists Activities for Kids Abbreviations & Acronyms Biology Physics Geology Astronomy Weather & Climate By Anne Marie Helmenstine, Ph.D. Chemistry Expert Ph.D., Biomedical Sciences, University of Tennessee at Knoxville B.A., Physics and Mathematics, Hastings College Dr. Helmenstine holds a Ph.D. in biomedical sciences and is a science writer, educator, and consultant. She has taught science courses at the high school, college, and graduate levels. our editorial process Facebook Facebook Twitter Twitter Anne Marie Helmenstine, Ph.D. Updated June 04, 2020 There are a few different ways you can make your own chemical cold pack. You could mix citric acid and sodium bicarbonate or you could mix barium hydroxide with an ammonium salt. If you have baking soda and vinegar, you can prepare your own hot ice or sodium acetate and then use the hot ice to make a cold pack. This method is pretty neat because crystallizing the sodium acetate generates a noticeable amount of heat. Dissolving the hot ice then absorbs the heat, so you can use the same chemical to make a hot pack and then a cold pack. Here's all you need to do: Hot Ice Cold Pack plastic bag with zipperhot icewater The hot ice needs to be sodium acetate trihydrate, which is the hydrated hot ice that you get right after you crystallize it. If you only have dry sodium acetate you need to dissolve it in the minimum amount of water and crystallize it. Now, just place your hot ice in the baggie and add a small volume of water. There you go... an instant cold pack! The reaction won't get super-cold (only about 9-10°C), but it's enough to be noticeable, plus the chemicals are re-useable.