Hot & Cold Pack Experiments
Chemical reactions that result in increased heat or cold are called exothermic or endothermic, respectively. These reactions produce results that are more extreme in temperature than any starting materials. You can explore exothermic and endothermic chemistry with easy experiments that can be customized for any age group or class size.
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Coldest Concentration
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Use multiple Styrofoam cups to determine what mixture of distilled water and ammonium nitrate results in the coldest mixture. Before beginning, cover the workspace with newspaper and make sure everyone is wearing safety goggles and latex gloves. Fill each cup with 100 ml of distilled water. Cut open an instant cold pack to remove the ammonium nitrate crystals and empty the crystals into a plastic bowl.
Measure the temperature of the water in the first cup. Add 10 g of ammonium nitrate to the water and stir with a plastic spoon. Record the temperature every 30 seconds or so until the temperature stabilizes. Pour the solution down the sink. Repeat the experiment in the second and subsequent cups, increasing the amount of ammonium nitrate in each cup by 10 g each time.
Determine which mixture was the most effective by subtracting the ending temperature from the beginning temperature for each cup. Graph the information on a line graph.
Coldest Chemicals
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Experiment with potassium nitrate, sodium chloride, calcium chloride and ammonium nitrate to determine which chemical creates the coldest cold pack. Fill four Styrofoam cups with 100 ml of distilled water. Add an equal amount of one of the chemicals to each cup and stir gently. Monitor the temperature in each cup continuously until it stabilizes and then begins decreasing. Evaluate the chemicals for temperature change and duration of the change.
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Rust Race
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Heat packs made from iron powder use the oxidation process to generate heat. Normally, the process occurs so slowly that the heat output is not noticeable. However, the iron powder in the heat packs rusts so quickly that a little pack can generate significant heat.
Determine how to make the iron rust fastest by experimenting with different ingredients. Distribute an equal amount of iron powder into three glass beakers. Do nothing with the first container, and pour water over the iron in the second container until all the iron is damp. In the third container, add that same amount of salt water.
Monitor the containers daily for changes. Document the daily observations and evaluate the data.
Hot Pack Variations
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Make a homemade hot pack from 25 g of fine iron powder or fillings, 1 g of salt and 1 tbsp. of fine sawdust or sand in a sealed plastic bag. Add five ml of water and seal the bag. To activate the heat pack, shake the bag.
Experiment with different measurements and larger pieces of iron or sawdust. Try leaving out various ingredients and evaluate the effectiveness of these variations.
Chemical Heat
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Some hot packs use sodium thiosulfate. Fill a test tube approximately half-full with sodium thiosulfate crystals and heat over a Bunsen burner until the crystals have melted. Let the liquid cool to room temperature.
To activate the reaction, place a single crystal of sodium thiosulfate into the liquid solution. Wait a minute or so to gauge the reaction. If there is no obvious change, place a second crystal in the solution. These crystals will cause the liquid to change to a solid, and as the substance changes, it releases heat energy.
Demonstrate how this heat pack can be reused by repeating the experiment. Heat the solidified sodium thiosulfate to a liquid and insert more seed crystals.
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