For this challenge, we were asked to create a hand warmer to sell during the cold winter sports practices and games, with a requirement for the hand warmers to increase by 20*C.
Our chemical of choice was Calcium Chloride. The combination of Calcium Chloride and water creates an exothermic reaction, therefore the materials together would create heat. After continuous cycles of trial and error, we came upon the perfect combination: 3.5 grams of Calcium Chloride and 20 mL of water.
After some calculations, we found that it would cost $28.58 to create 100 hand warmers, and $0.28 for each one. We would sell each for $1.00. We will also be selling reusable wool pouches to ensure the absolute highest level of warmth. These will cost $2.00 initially, but by bringing the pouch the next time you purchase a hand warmer, your hand warmer will be half off ($0.50).
Our final product turned out to be two separate compartments, one side filled with water and the other with Calcium Chloride. Space was left at the top, and clipped down when not in use. When the clip is released, the salt and water can mix. Within 15 seconds, the temperature will raise drastically. Without the outer pouch it will stay warm for 4 minutes, and with the outer pouch it will stay warm for 8-10 minutes.
Through calculations, we found that the enthalpy of cold water was 59,831 and the enthalpy of hot water was 6,568. Our enthalpy change of the calorimeter was 585.7, and the calorimeter constant was 19,52. The calorimeter constant for all trials was 337.216 J/g*C.
The hardest part of this project for our group was the calculations. It took us a while to understand how to do them, and then even longer to understand how to apply them to our hand warmer. We also had a problem with the clip in our design. We could not find a clip that would seal tight enough to keep the water from seeping through. With more time and resources, we could easily work through these difficulties.