OUR PROJECT
The goal of this project was to create a safe, cheap, long lasting hand warmer that we could then sell at our student store on campus.
We started our project by finding out what materials we were going to use for our hand warmer. We tested many different salts that produce heat when touching liquid water. Lithium Chloride was the salt that created the fastest and hottest temperature change, so we decided to use that.
Next, we planned several different designs for the hand warmer. We eventually landed on our final design for a plastic pouch covered with flannel. The pouch has one thicker, outer layer and a smaller, less durable inside bag. The smaller bag is just the correct size to hold 14ml of water and then there is enough space left in the outer bag to put in 2g of LiCl. We did several different tests with varying amounts of salt and water and eventually found a nice temperature change with this ratio of salt and water. We covered the larger plastic pouch with a flannel pouch that was sewed. The pouch has one side with an open flap that we sewed a quarter shut on each end of the pouch. With this, the plastic hand warmer can be removed from the flannel pouch, but is stuck in there so it won't fall out easily.
We started our project by finding out what materials we were going to use for our hand warmer. We tested many different salts that produce heat when touching liquid water. Lithium Chloride was the salt that created the fastest and hottest temperature change, so we decided to use that.
Next, we planned several different designs for the hand warmer. We eventually landed on our final design for a plastic pouch covered with flannel. The pouch has one thicker, outer layer and a smaller, less durable inside bag. The smaller bag is just the correct size to hold 14ml of water and then there is enough space left in the outer bag to put in 2g of LiCl. We did several different tests with varying amounts of salt and water and eventually found a nice temperature change with this ratio of salt and water. We covered the larger plastic pouch with a flannel pouch that was sewed. The pouch has one side with an open flap that we sewed a quarter shut on each end of the pouch. With this, the plastic hand warmer can be removed from the flannel pouch, but is stuck in there so it won't fall out easily.
chemistry
The basis of our handwarmer is this chemical reaction:
LiCl(s) + H2O -> Liᐩ(aq) Cl⁻(aq) + H2O + Heat
Lithium Chloride and water yields Lithium cations, Chloride anions, water and heat. The specific type of reaction is an exothermic reaction. This means that heat is released externally out of the reaction. This occurs because the amount of heat required to separate the lithium and chloride is less heat than is released after the reaction, so some heat is released.
We also calculated the heat produced from our reaction using the formula Q = mc * change T. We solve for the heat Q in this case. We know that the mass is that of the lithium chloride, which is 2 grams, the specific heat of water is 4.185J/gC, and that the change in temperature of the water was . Multiplying all of these numbers gets Joules of heat produced by our handwarmer.
LiCl(s) + H2O -> Liᐩ(aq) Cl⁻(aq) + H2O + Heat
Lithium Chloride and water yields Lithium cations, Chloride anions, water and heat. The specific type of reaction is an exothermic reaction. This means that heat is released externally out of the reaction. This occurs because the amount of heat required to separate the lithium and chloride is less heat than is released after the reaction, so some heat is released.
We also calculated the heat produced from our reaction using the formula Q = mc * change T. We solve for the heat Q in this case. We know that the mass is that of the lithium chloride, which is 2 grams, the specific heat of water is 4.185J/gC, and that the change in temperature of the water was . Multiplying all of these numbers gets Joules of heat produced by our handwarmer.
Marketing
The main goal of our handwarmer was to create a decently warm one that lasts for a while, but is very cheap. Our handwarmer uses very small amounts of material, allowing it to be sold for very little. With the average material cost, it is only 60 cents for a new handwarmer, and 20 cents for a lithium chloride packet refill. Many other groups created a handwarmer that would be very costly(upwards of 2 dollars), but ours is a convenient size, lasts for a decent amount of time, and costs very little, allowing many to be sold at one time.
Our presentation
Reflection
Our group struggled at the beginning developing a solid idea for a handwarmer. Many other groups found unique and very good-working chemistry that made for a nice handwarmer. We stuck with the basics like a couple other groups and went for a lithium chloride packet. We could improve by using more time on finding unique handwarmers like other groups and also really testing our handwarmer. We got caught up in creating them so much that we didn't get to really test them and they weren't very warm. Our group did always have something to do and were on task as well as communicating our ideas about the project well with each other.