Project Description
In this project we were assigned to build a handwarmer that is environmentally friendly, marketable, safe, and effective. We started this unit by researching calorimetry and endothermic/exothermic reactions. We later tested a series of salts to determine if they would release energy when mixed with water.
For our handwarmer, we decided to use sodium acetate instead of lithium chloride, and we produced a phase change reaction instead of a chemical reaction. The advantages to this were that we could repeat this reaction many times, meaning that our hand warmers are reusable.
For our handwarmer, we decided to use sodium acetate instead of lithium chloride, and we produced a phase change reaction instead of a chemical reaction. The advantages to this were that we could repeat this reaction many times, meaning that our hand warmers are reusable.
Our PRoject Presentation
CHEMISTRY concepts
As said before, the heat from our handwarmer was put off from a phase change reaction.
The liquefying and solidifying of sodium acetate hydrate can be represented by:
NaC2H3O2 3H2O(l) > NaC2H3O2 3H2O(s) + heat
NaC2H3O2 3H2O(l) > NaC2H3O2 3H2O(s) + heat
- The forward reaction which creates the heat in a hand warmer is an exothermic reaction. This is a negative free energy change. This represents the crystallization process.
- The reverse reaction which is the melting process is an endothermic reaction with a positive free energy change. This was evident by the need to add heat to, or boil the pouch.
Our prototype is both supersaturated and supercooled. Supersaturated and supercooled means that there is more sodium acetate than the saturated solution and the sodium acetate has been cooled below its freezing point of 54*C without crystallization. In a sealed container, the solution can be cooled to -10*C without freezing.
The metal disc serves as the nucleation site, or where the reaction occurs. When bent, a single molecule of sodium acetate trihydrate to crystallize and act as a seed crystal that starts the chain reaction.
The metal disc serves as the nucleation site, or where the reaction occurs. When bent, a single molecule of sodium acetate trihydrate to crystallize and act as a seed crystal that starts the chain reaction.
reflection
During this project, my group and I has a lot of fun constructing and building our model, and we learned a lot. Firstly, building a real hand warmer from our own work forced us to understand the chemistry behind phase change reactions and crystallization very well in order to perfect our prototype and properly explain it to the class. Maybe more importantly, we learned how to work well as a group to effectively and efficiently get the job done. We knew our strengths and weaknesses well, both as individuals and as a group. This allowed us to work more efficiently and divide ourselves among tasks. Although it is hard to come up with two things we could have done better at, I think that we could have thought out our original prototype more thoroughly before wasting sodium acetate on failed experiments. Because we finished both our final product and our presentation early, we could have also spent more time on the marketing side of the project and conducted a survey to determine how much students would actually pau for a hand warmer like ours. Overall, this was one of my favorite projects of the last few years, partially because of the excitement of making a unique product from our own ideas, partially because of how well our group worked together.