Our assignment was to create a hand warmer that increased in temperature by 20 C as quickly as possible and had a volume of around 50 mL, while using cheap, safe, and effective materials along the way. At the end, the goal was to sell the best hand warmer in the student store for winter sports fans. There were many factors that we had to consider during the design process, such as what salt to use, how to properly seal the plastic bags, how to keep the water and salt separate, the size of the hand warmer, and the ratio of salt to water. Before we even started building the prototype, we tested six other salts to discover their ability to hold heat and change temperature. After conducting these tests and recording data, we saw through our results that Calcium Chloride (CaCl2) was the best salt to use. We had three different trials of amounts of water and Calcium Chloride before figuring out the perfect amount. First, we had 5 grams CaCl2 and 50 mL of water. This amount was not successful because there was not enough of the salt to react with the water. Next we tried 30 grams of CaCl2 and 10 mL of water, which was too much salt and not enough water, so it absorbed all the water quickly. Finally, we tried 10 grams of CaCl2 and 25 mL of water, which was a perfect ratio and the hand warmer stayed warm for the longest amount of time yet. We discovered the reaction to be exothermic, since heat is being released. The chemical formula for this reaction is CaCl2 + H2O ---> Ca(OH)2 + 2HCl or, in word form, calcium chloride reacts with water to produce calcium hydroxide and hydrogen chloride. In the presentation attached below, you can see pictures of our hand warmer, calculations, and other useful information:
Reflection
I had a very positive experience with my group. I thought the majority of this project went well. We had good ideas and tested them accurately and effectively. I think the only part of the project that we struggled with was the sealing of the bags, as well as the amount of plastic that went into this project as a whole. New skills I gained were learning how to calculate enthalpy change and calorimeter constants for different salts, as well as using a bag sealer for the first time. It was interesting to learn the chemistry behind what was going on in the reactions. Some skills that I could work on improving are evenly distributing my work and getting more involved with construction. I did most of the calculations for our group, and did a lot of the presentation as well. However, I did not work a lot on the actual testing and building of the model. In the future, I could try harder to work on all aspects of the project. One peak during our project was when we finally figured out the proper ratio of salt and water, as well as when Ms. Vogl observed that our hand warmer was staying warm for the longest that she had felt yet, which was very rewarding. Some pits that we experienced were when we could not figure out how to seal the plastic bags after trying to days. It was also a pit because we used large amounts of plastic trying to seal the bags to prevent leaks, which is a waste of resources and bad for the environment, too. Overall, I learned a lot during this project and had a positive experience while doing so.