Engineering Chemical Cold Pack Reactions

In this lesson, students design a prototype instant cold pack system that absorbs thermal energy using an endothermic chemical reaction.

• Engineers play an important role in society, applying scientific knowledge to create new technologies that solve problems.
• Like scientists, engineers follow a process to guide them as they develop technologies that solve problems.
• Chemical cold packs are an example of a technology because humans designed to solve a problem.
  
  

• What is the role of technology in the STEM cycle?
• Why is it important for engineers to follow a process?
• How are the scientific and engineering processes different from each other?
• Why are chemical hot and cold packs examples of technologies?
• How do instant hot and cold packs modify something from the natural world in their design?
• How do engineers use scientific knowledge about chemical reactions to design instant cold packs?
  
  

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.
 
Step 1: Identify 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.