Hands-on Activity Hot Potato, Cool Foil

Learning Objectives

After this activity, students should be able to:

• Explain that heat capacity is the amount of heat a quantity of a substance can absorb/release when changing by one unit temperature.
• Explain that material properties and tolerances are important in the design and construction of engineering projects in order to assure functionality and safety as well as exploit a substance's natural abilities to solve a problem.

Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

NGSS: Next Generation Science Standards - Science

Common Core State Standards - Math

International Technology and Engineering Educators Association - Technology

State Standards

Materials List

Each group needs:

• a calorimeter (Note: The associated Counting Calories activity provides instructions for students to build their own calorimeters.)
• a stir rod or Popsicle® stick
• thermometer
• 1 piece of aluminum, ~75g
• 1 piece of copper, ~75g
• an object of their choice (rubber, wood, rock, etc.), ~75g
• tongs, to hold the samples
• As Cold as Ice Worksheet, one per student
• To Heat or Not to Heat Worksheet, one per student
• Do You Have the Capacity? Worksheet, one per student

Each group should have access to:

• a freezer

Worksheets and Attachments

Pre-Req Knowledge

Algebra: Students need to know how to perform basic algebraic manipulation of equations and substitution techniques.

Physical Science: Students should be familiar with the concept of energy, that it can be exchanged, and that it comes in different forms.

Introduction/Motivation

Different materials hold different amounts of heat. For example, think of a baked potato wrapped in aluminum foil freshly removed from an oven. Initially, both the potato and the foil are at the same temperature, the oven temperature. However, after several minutes exposed to the room temperature air, there is a large difference in temperature between the foil and the potato. The potato is still very hot, whereas the aluminum foil has already cooled to the ambient air temperature.

Why is this? Many factors contribute to this interesting phenomenon, but what we are interested in is the specific heat, or heat capacity. Heat capacity is the amount of energy a substance can absorb while increasing in temperature. Objects with a high heat capacity can absorb a lot of energy before getting hotter, while things with a low heat capacity only need a little energy before changing temperature. Since the aluminum has a lower heat capacity, it contains less energy and thus cools more quickly to room temperature. Our baked potato on the other hand has a higher heat capacity, and has a lot more energy to release before it cools down again.

Understanding this phenomenon is an important part of engineering. By understanding this and other material properties, engineers ensure the materials they are working with stay safe and are reliable. Aerospace and mechanical engineers need to know the amount of heat a material can absorb in a space vehicle or automobile in order to ensure it does not overheat and explode or disintegrate. Chemical and biological engineers need to know how much energy it will take to heat substances to an appropriate reaction temperature for ideal chemical or biological synthesis. Other engineers can use this information for everything from cooling systems in buildings to operating temperatures in circuits. Knowledge of heat capacity is obviously a very important connect for engineering.

Procedure

Background

[For teachers] If students have already completed the Counting Calories activity, have them reuse their calorimeter for this activity. If you do not have manufactured calorimeters or if the students did not save their calorimeters from the Counting Calories activity, have students build their own calorimeters at this point. (Refer to the instructions in the Counting Calories activity or see below.)

Simple Calorimeter: With two Styrofoam® coffee cups, nest one into the other. Take a plastic lid for one of the coffee cups and cut two holes in the top approximately the diameter of a pen. These holes are for thermometer and stir rod access. If a glass stir rod is not available, use a Popsicle® stick. Make sure that the lid opens so that students can access the contents of their calorimeter.

Before the Activity

• Have students weigh their material samples before putting them in the freezer.
• Make sure to put each group's three materials of interest into the freezer at least an hour in advance of the activity.
• Place a thermometer in the freezer to measure the freezer temperature.
• The students need to be able to transfer their sample quickly between the freezer and the calorimeter. Provide plenty of desk/counter space next to the freezer for students to conduct their experiments.
• Make enough copies of each worksheet so that each student gets their own.

[For students]

Calculations

To determine the heat capacity, we first must know some important equations. First, the heat (Q) is related to the change in temperature (T) by the heat capacity C_P for a given number of moles (n). The equation we get is as follows: Q=nC_P∆T

In this case, we want to use the heat, moles and temperature change of the water and the blocks to calculate C_P .

With the Students

1. Before the activity, have the students read the introduction on the As Cold as Ice Worksheet.
2. As a class, discuss the questions on the Do You Have the Capacity? Worksheet. If necessary, guide the discussion towards the subject of heat capacity.
3. If the students are building calorimeters, distribute the materials and demonstrate the construction. If not, then tell students to retrieve their calorimeters from the previous activity.
4. The students should follow the instructions given on the As Cold as Ice Worksheet.
5. The students will fill their calorimeter with 100ml of water and wait for it to equilibrate with its surroundings.
6. The students will record the temperature of their water and the freezer temperature.
7. Quickly, the students should use the tongs to transfer their samples from the freezer to their calorimeter. Instruct them to seal the calorimeter very quickly!
8. The students will record the lowest temperature the thermometer reaches and do the calculations on their As Cold as Ice Worksheet.
9. After the activity, give the students the To Heat or Not to Heat Worksheet to complete in their groups.

Vocabulary/Definitions

enthalpy: A value which describes the amount of energy in a system including pressure and volume, relative to a reference state.

heat: Energy transferred between two systems as a result of a temperature difference.

heat capacity: The amount of energy transfer required to raise or lower a given amount of a substance by one unit temperature at a constant pressure.

Assessment

Pre-Activity Assessment

Accessing Prior Knowledge: Have the students complete the Do You Have the Capacity? Worksheet to start them thinking about heat capacity. Review their answers to gauge their mastery of the subject.

Activity Embedded Assessment

Worksheet: Have the students follow along with the As Cold as Ice Worksheet. Review their answers to gauge their mastery of the subject.

Post-Activity Assessment

Reflection: Have the students complete the To Heat or Not to Heat Worksheet. On this worksheet, they calculate the accuracy of their calculations as well as suggest improvements for the next iteration of the design. Have them share their ideas with the class. Review their answers to gauge their mastery of the subject.

Troubleshooting Tips

• If the calorimeters are empty, the thermometer will likely be heavy enough to tip the device over and possibly break the thermometer. Therefore, instruct student to not leave their thermometer in an empty calorimeter.
• Make sure to transfer the cold metals into the calorimeter quickly and instantly be prepared to record the temperature change. The heat exchange happens quickly and is easy to miss.
• Do not touch the cold sample with anything other than the tongs! This will instantly skew the results as heat from your fingers will transfer to the material. Use only the tongs to transfer the material object between the freezer and the calorimeter.
• It may be somewhat difficult to obtain the metal pieces. A local machine shop may have scrap aluminum or copper that they will provide free of charge or for a low cost. Failing that, hardware stores sell lengths of pipe; a piece in that form is suitable. Finally, if only a couple pieces of each material type can be found, then simply have groups share each piece of metal and take turns with them rotating through the steps.

Activity Extensions

Have students go online or to a library to learn more about heat capacity and specific heat. For example, find equations describing how heat capacity can be calculated for different temperatures or how it changes with temperature. Also, the students should report on why different substances hold more heat than others.

Activity Scaling

• For lower grades, do the activity as a demonstration for the entire class.
• For upper grades, do the activity as is.

References

Copyright

Contributors

Supporting Program

Acknowledgements

The contents of this digital library curriculum were developed under a grant from the Fund for the Improvement of Postsecondary Education (FIPSE), U.S. Department of Education and National Science Foundation GK-12 grant no. 0338326. However, these contents do not necessarily represent the policies of the Department of Education or National Science Foundation, and you should not assume endorsement by the federal government.