Summary

In this project, students will use their knowledge of thermodynamics to design a handwarmer for a manufacturing company that can maintain a temperature of 30-40°C for at least 5 minutes and is designed to fit in the average human hand. Students will create a final product after rounds of testing and an advertising poster that summarizes the results of their testing and promotes their design.

Grade Level

High School

NGSS Alignment

This project will help prepare your students to meet the performance expectations in the following standards:

• HS-PS3-1: Create a computational model to calculate the change in the energy of one component in a system when the change in energy of the other component(s) and energy flows in and out of the system are known.
• HS-PS3-3: Design, build, and refine a device that works within given constraints to convert one form of energy into another form of energy.
• Scientific and Engineering Practices:
  • Using Mathematics and Computational Thinking
  • Developing and Using Models
  • Analyzing and Interpreting Data
  • Constructing Explanations and Designing Solutions

AP Chemistry Curriculum Framework

This project supports the following unit(s), topic(s) and learning objectives:

• Unit 6: Thermodynamics
  • Topic 6.1: Endothermic and Exothermic Processes
    • ENE-2.A: Explain the relationship between experimental observations and energy changes associated with a chemical or physical transformation.
  • Topic 6.4: Heat Capacity and Calorimetry
    • ENE-2.D: Calculate the heat q absorbed or released by a system undergoing heating/cooling based on the amount of the substance, the heat capacity, and the change in temperature
  • Topic 6.6: Introduction to Enthalpy of Reaction
    • ENE-2.F: Calculate the heat q absorbed or released by a system undergoing a chemical reaction in relationship to the amount of the reacting substance in moles and the molar enthalpy of reaction.

Objectives

By the end of this project, students should be able to:

• Design and engineer a final product that utilizes at least one form of energy.
• Explain how their product works with regards to energy transfer, exothermic reactions, and calculations of energy released and/or absorbed with enthalpies and specific heat capacities.
• Make a claim about the effectiveness of their handwarmer and support their claim with data on their advertising poster.

Chemistry Topics

This project supports students’ understanding of:

• Conservation of energy
• Heat transfer
• Exothermic and endothermic processes
• Enthalpy
• Engineering design and development

Time

Teacher Preparation: 30-60 minutes
Lesson: anywhere from 2-4 hours spread over several days. (This may take more or less time depending on the amount of prototyping students need to do in order to complete the task for the final design and poster production.)

Materials

• Goggles and aprons
• Various chemicals, including:

• Scoopulas, beakers, and graduated cylinders for whatever chemicals you use
• Balances and weigh boats
• Temperature probes and Vernier lab quest OR thermometers
• Ziplock bags in snack, sandwich, and quart sizes
• Twist-ties
• Student-provided design materials to make a realistic, sellable product (such as fabric/cloth to contain and “dress up” their final product)
• Poster board
• Markers/pens/colored pencils

Safety

• Always wear safety goggles when handling chemicals in the lab.
• Students should wash their hands thoroughly before leaving the lab.
• When students complete the lab, instruct them how to clean up their materials and dispose of any chemicals.

Teacher Notes

• This is a project that is used to apply concepts of thermodynamics to a real-world problem. Students should have already explored concepts of thermodynamics, including energy, conservation of energy, system and surroundings, calorimetry, enthalpy, and specific heat capacities and calculations.
• This could be used in a thermodynamics unit or as a post-AP Exam/end-of-year activity.
• This project can be introduced at the beginning of your thermodynamics unit to get the students thinking. Then throughout your thermodynamics unit you can stop and have your students modify their models/designs as they gain the secondary knowledge. This will allow for their design ideas to evolve throughout the unit.
• To cut down on the quantity of supplies needed, you could have students work in small groups of 2 or 3. This also gives them the opportunity to develop ideas with their peers, which better represents real-world engineering projects. In this case, you may wish to have them evaluate their teammates throughout the process so that you can intervene if some students seem to be doing all the work or not allowing others on their team to participate fully.
  • Students are given the option to do a smaller scale run (~5 g reactants) as proof of principle for any reaction they might use as part of their design before building their first prototype to ensure their heating method is a viable option.
• It can be hard to let the students come up with their own models. Some students will only want to use rice to make a rice bag but then they soon realize it is not practical because they have no way of activating it at a football game unless they heat it up before they leave. Stay open minded and understand that their projects/models may change drastically as they continue to collect knowledge and discuss with their peers.
• By the end, most students end up using combinations of chemical energy along with the specific heat capacity of water and rice to create interesting designs. Some of the best designs involve the use of calcium chloride in one pouch, water in another, and then one can activate it by squeezing it. Some students then connect it to rice which allows the heat to sustain longer and not run out so quickly or disperse into the surroundings. Below are some images of previous work:

• Some students used electrical energy (batteries and wires) to make gloves that warm up, trying to recreate electric heating pads/blankets. They used voltage and an equation to calculate Joules of output from their design. I usually try to redirect students from this method due to safety concerns. You could tell them up front that they cannot be battery powered if you wish.
• The calculations section will look different for each student/group, depending on the design of their product. They will all involve temperature change, and they will need to know the mass (and formulas/molar masses of chemicals) if they plan on using specific heat calculations or enthalpy of reaction. They would need to look up specific heat capacity and enthalpy of reaction values for the substances/reactions they use.
• Students will be bringing in their own design materials. (You may want to have a selection of materials for low-income students to choose from if cost is going to present a barrier to their participation in this project.) For example, if they want to turn a stuffed bear into a handwarmer, they will provide it, or if they want to create fleece handwarmers, they will bring in the fleece along with the tape or thread needed to complete the fleece pouch. Let students know this ahead of time.
• Encourage students to use materials that make their product resemble a real, sellable item. They will need to create their products with their own designs in mind so temperatures can be collected appropriately.
• A suggested rubric is available for download in the sidebar. You could modify it as you desire. You could also provide it for students at the outset of the project so they know how they will be evaluated for this project.
• If time allows, you could substitute a presentation to the class for the poster. Each student or group could “pitch” their product and gain public speaking experience. The requirements for the poster could be included on a PowerPoint (or similar) presentation instead.