Science teachers will demonstrate the creation of hot ice for the purpose of creating an instant re-usable cold pack in an experiment that requires only three materials. Provide students with a gallon freezer bag, 10g of dry sodium acetate and water. Hydrate the sodium acetate with water according to package instructions for crystallization. Add the crystals to the freezer bag and fill approximately halfway with water. The water is eventually absorbed by the sodium acetate or evaporates, and the sodium acetate crystals are re-usable to make cold packs when needed.
Distribute a foam cup and instant cold pack to each student and instruct them to add 100ml of distilled water to the cup. Cut open the cold pack and remove the ammonium nitrate crystals pouch. Remove 10g of crystals. Record the temperature of the water in the cup. Add the ammonium nitrate and stir, checking the temperature every 30 seconds until it stabilizes. Calculate the enthalpy and entropy changes that occur during the reaction at each 30-second interval.
Students concerned with "going green" can experiment with cold packs and manure to learn about endothermic and exothermic reactions. Gather an instant cold pack, four gallon freezer bags and three different brands of manure. Cut the cold pack open and remove the water and crystal pouches. Break into a freezer bag and shake vigorously. Insert a thermometer into the bag after 10 minutes to record the temperature. Place an amount of fertilizer equal to the weight of the instant cold pack in each of the remaining gallon-size bags. Add the same weight in water to each bag and shake to mix. Record the temperature of each bag after 10 minutes. Conclude whether environmental cold packs are effective based on the data collected.
Teachers with access to multiple chemicals enable students to attempt different combinations and discover which elements create the most effective cold packs. Provide samples of barium hydroxide, ammonium salt, calcium chloride, and sodium bicarbonate, in addition to rubbing alcohol, citric acid and water. Encourage students to experiment by combining different powders and salts with the various liquids and record the temperature in each cold pack. Students should present their findings in a report prior to a class vote on which chemical combination produced the best instant cold pack.