EXOTHERMIC REACTIONS USED IN HOT PACKS

• Jayne Warner - Waterloo Middle School
• Candace Culbertson - Waterloo Middle School
• Janice Evanovich - Waterloo Middle School
• Katie Francis - Waterloo Middle School, student
• Steve Work - Waterloo Middle School, student

Waterloo Middle School

1776 St. Rt. 44

Randolph, OH 44265

Phone: 216-325-7272

Internet address: waterlms@phoenix.kent.edu

Middle School (Grades 6, 7, 8)

Applications for chemistry, physics, life science, general mathematics,

algebra and media.

 An ever increasing interest in physical exercise often leads to secondary painful muscle spasms. It has been shown that hot packs which create an exothermic chemical reaction can be used to effectively relieve muscle soreness through heat therapy.

 With these ideas in mind, this experiment is designed to determine the safe and effective temperature range resulting from an exothermic reaction. By dissolving different proportions of the common household chemicals calcium chloride (rock salt) and sodium hydrogencarbonate (baking soda) in distilled water, this effective temperature range can be found.

 Also this experiment is designed to serve as an introductory lesson into the properties of cholesteric liquid crystals. Because they have the unique ability to change color with fluctuating temperature, the liquid crystals can be used to monitor the temperatures of the assembled hot packs.

 After completion of the experiment, a new set of questions will be raised. Will these homemade heat packs be cost-effective and therapeutically valuable? Will the temperature range be easily monitored by the user to avoid burns?

 MATERIALS:

• heavy-duty zip-lock bags
• 500 ml distilled water
• cholesteric liquid crystal strips
• thermometer (optional)
• 50 g calcium chloride (rock salt)
• 50 g sodium hydrogencarbonate (baking soda)

• Eagleson, Mary. Concise Encyclopedia of Chemistry. Berlin: Walter de Gruyter & Co., 1993.
• Gahl, Jim. Science Toolkit Plus: Master Module. Broderbund Software Inc.. San Rafael, CA, 1989.
• Lehman, Justus F. Therapeutic Heat and Cold. London: Williams & Wilkins, 1982.
• Nyre, William. "Endothermic and Exothermic Reactions," Grolier Electronic Publishing, 1995.
• Nyre, William. "Thermochemistry", Grolier Electronic Publishing, 1995.

• SCIENCE:

 The student will:

1. Have a basic understanding of the scientific method.
2. Make predictions of the outcome of the experiment.
3. Collect, record and interpret the data.
4. Analyze experiment outcomes.
• MATH:

 The student will:

1. Use data to create:
• line graph
• bar graph
• scattergrams
2. Find a median for the set of data gathered.
3. Find the slope and equation of the line graph.

1. Research calcium chloride and sodium hydrogencarbonate compounds.
2. Research the uses of therapeutic heat applications through conduction.
3. Research exothermic reactions and thermochemistry.
4. Research cholesteric liquid crystals. Much of this can be done on the Internet or in the school's media center.
5. Students should make predictions about experiment outcomes before beginning to use information gathered from research. They should predict which proportion of ingredients would produce the safest therapeutic heat.

1. Put given ratios of compounds in zip-lock bags onto which cholesteric liquid crystal strips have been attached.
2. Take initial temperature readings and record data.
3. Add given amount of distilled water to "hot packs".
4. Record the time it takes to get to the maximum temperature.
5. Record the time that the maximum temperature is maintained.
6. Determine if the temperature range is within the desired therapeutic range.
7. Repeat experiment for other ratios of the compounds.

1. Did the outcomes meet your predictions? Explain.
2. Which ratio produced the most desirable therapeutic temperature?
3. Would a liquid crystal strip on a hot pack be useful? Why?

1. Guest speakers on the subject of sports medicine.
2. "Ask a Scientist" via the INTERNET for any unanswered questions.
3. Comparison of commercially made hot packs with those that the students made. (Compare cost and/or effectiveness)

This activity has been copied, with permission, from the Kent State University server to ours, to allow faster access from our Web site. We encourage you to explore the original site.

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