In this lesson, students design a prototype instant cold pack system that absorbs thermal energy using an endothermic chemical reaction.
In this unit, students explore several phenomena that relate to cooking. In this lesson, students evaluate chemical reactions, and use that knowledge to engineer a prototype that transfers energy by chemical processes. This page showcases key components of this lesson.
Science background gives teachers more in-depth information on the phenomena students explore. Below is an excerpt from the science background section on engineering chemical cold pack reactions.
Engineers use scientific knowledge about heat transfer and chemical reactions to design solutions that involve heating something up or cooling something down. An engineer is anyone who uses scientific knowledge and mathematics to design a technology that solves a problem.
Similar to how scientists follow a process to answer a question, engineers also follow a process that often includes eight steps to guide them as they create new technologies to solve problems. The engineering process always begins with a problem. When engineers are defining a problem, they include the criteria (the needs the solution must meet) and constraints (ways the solution is limited). Available materials and cost are two common engineering constraints.
After engineers have researched their problem, they survey the available materials. This survey includes a sketch of the material, as well as how much of the material they have available and the properties of that material.
Engineers then come up with possible solutions for how the problem can be solved with the available materials. For example, one possible solution is to combine two substances, such as water and ammonium nitrate (NH4NO3), which create an endothermic reaction when combined. The two substances will have to be separated by a barrier that can be broken so the two substances can combine and react when the pack needs to become cold.
The next step is to diagram and build a prototype. A prototype is a scaled-down first draft of a technology. Once built, engineers test the prototype. They use the tests to gather data, which are measurements and observations that capture how well the prototype solves the problem during testing.
The data tell engineers whether their prototype technology solved the problem. Engineers use this data to decide whether to refine or replicate. For example, engineers would evaluate how cold their ice pack became and determine whether that was cold enough to keep food and drinks temporarily cold.
New technologies can also be used to solve other problems. For example, chemical cold packs have been designed so they can be used on people to reduce swelling and ease muscle pains. One challenge for the instant cold pack is what kind of material to wrap the reacting substances in. It has to be flexible enough to fit the natural curves of the human body. It also has to be insulated so that it didn’t become so cold that it burned the person using it. Engineers use natural resources to design synthetic materials that have a specific function. A synthetic substance is one that is formed through a chemical process developed by humans, as opposed to those of natural origin.
In this lesson, students design a prototype instant cold pack system that absorbs thermal energy using an endothermic chemical reaction.
Prepared hands-on materials, full year grade-specific curriculum, and personalized live professional development designed to support mastery of current state science standards.
Misconception: The atoms of the reactants in a chemical reaction are transformed into other atoms.
Fact: The atoms aren’t changed into other atoms. Instead, the atoms stay the same but rearrange to form new molecules.
Chemical reaction : a change that rearranges the atoms of the original substances into a new substance that has different properties from the original substances
Engineer : anyone who uses scientific knowledge and mathematics to solve problems by creating new technologies
Endothermic : a process in which energy is absorbed from the environment
Exothermic : a process in which energy is released into the environment
Molecule : a combination of two or more atoms bonded together
Potential energy : energy that is stored
Property : an observable or measurable characteristic of a substance
Prototype : a scaled-down first draft of a technology
Synthetic : substances formed through a chemical process developed by humans, as opposed to those of natural origin
Temperature : a measure of heat; measured in Celsius with a thermometer
Preserving Food
No food will last forever. In time, all foods decay. When this happens, we can no longer eat them. Before people had refrigerators and freezers, they used blocks of ice in a container to keep foods cold. The cold slowed down decay. When refrigerators and freezers were invented, they helped solve the problem of food spoiling by keeping foods fresh for longer periods of time.However, it was still difficult to keep foods cold for extended periods of time when you didn’t have access to a refrigerator.
Engineering Solutions
In the 1950s, engineers began using what they know about heat transfer and chemical reactions to design instant cold packs. Engineering is different from science, although science and engineering are connected. Remember the STEM cycle. Scientists use experiments to gain knowledge. Engineers use that scientific knowledge and mathematics to create new technologies that solve problems. A technology is anything that people have modified from the natural world to meet their needs and wants.
Similar to how scientists follow a scientific process to answer a question, engineers also follow a process. Engineers often follow a process with eight steps that guides them as they create new technologies to solve problems. The engineering process is similar to the scientific process but it differs because each has a different goal. Scientists are trying to answer a question, while engineers are trying to solve a problem.
The engineering process begins with a problem. When engineers are defining a problem, they include the criteria (the needs the solution must meet) and constraints (ways the solution is limited).
Step 2: Research the problem.Once they have identified the problem, engineers need to research it to find out what is known about the problem.
Step 3: Survey available materials.After engineers have researched their problem, they survey the available materials. This survey includes a sketch of the material, as well as how much of the material they have available and the properties of that material.
Step 4: Come up with possible solutions.Engineers then come up with possible solutions for how the problem can be solved with the available materials.
Step 5: Diagram and build a prototype of the solution.Once engineers come up with a possible solution, they diagram and build a prototype. A prototype is a scaled-down first draft of a technology.
Step 6: Test the prototype.Once built, engineers test the prototype. They want to see how well it works and whether it meets the criteria of the problem within the constraints.
Step 7: Collect data.They use the tests to gather data about how well the prototype solves the problem during testing.
Step 8: Refine or replicate.Finally, engineers use their data to decide whether to refine or replicate. If the prototype doesn’t work in some way, engineers know they need to refine their design. They need to look at what didn’t work and come up with ways to improve it. If the prototype solved the problem, meeting the criteria within the constraints, the engineers will replicate their design.
For the engineering activity of this lesson, students design a prototype instant cold pack system that absorbs thermal energy using an endothermic chemical reaction. Students design a possible solution to the problem and develop a method for testing the cooling effects of their prototype. They collect and analyze data on the temperature change of their prototypes when different amounts of reactants are added to the reaction. Then, students use the data and observations from their prototypes to describe how their modifications positively or negatively affected the final temperature reached by the reaction.
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Standards citation: NGSS Lead States. 2013. Next Generation Science Standards: For States, By States. Washington, DC: The National Academies Press. Neither WestEd nor the lead states and partners that developed the Next Generation Science Standards were involved in the production of this product, and do not endorse it.