Science Activity
#7 - Hot Pack / Cold Pack
All experiments must be done in the presence of a parent or teacher.
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Ideas
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Key Words
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Materials
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Procedure
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Observations
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Summary
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Questions
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WWW Links

Ideas to be Developed

Chemicals can store energy and release it in the form of heat. A chemical reaction that releases heat is called an exothermic reaction. But chemical reactions can also absorb heat from the environment and get cold. These reactions are called endothermic reactions. When chemicals are dissolved in water, sometimes heat is released, and sometimes heat is absorbed.


Heat is given off as a result of a chemical reaction.
Hot/cold packs are used by athletes to minimize swelling of injuries such as muscle and joint sprains. They are constructed of a large pouch containing a dry chemical plus an inner pouch of water. The hot/cold pack is activated by breaking the seal on the pouch of water and shaking the pack vigorously. This action mixes the water with the chemical starting the exothermic or endothermic reaction.

If the dissolving of the chemical in water is an endothermic process and absorbs heat energy, it is a good candidate for making a cold pack because this process will lower the temperature of the content of the pack. If the dissolving of the chemical in water is an exothermic process and releases heat energy, it is a good candidate for making a hot pack because this process will raise the temperature of the content of the pack.


Key Words
Chemical Reaction - When substances are mixed and new substances are formed, a chemical reaction has occurred.
Endothermic
- A chemical reaction that absorbs heat from the environment is called an endothermic reaction.
Exothermic - A chemical reaction that releases heat is called an exothermic reaction.

Materials Required
Bring a hot pack from home for class discussion (if available).
Bring a cold pack from home for class discussion (if available).

Procedure
DEMO with class participation

Which of the following substances would make a good hot pack or cold pack?


Chemicals:
  • ammonium nitrate, NH4NO3
  • calcium chloride, CaCl2
  • sodium chloride, NaCl
  • sodium acetate, NaCH3COO
  • ammonium chloride, NH4Cl

Demo #1:
1. Label the baggy with the name of the chemical.
2. Fill a baggy with 50 mL of water and dissolve 50 grams of compound in the baggy.
3. Pass the baggy around and let students feel the baggy.

Demo #2:
1. Demonstrate a commercial hot pack/cold pack.


Demo #3: (Reading a thermometer properly)
1. Set up 2 thermometers and stands and fill two beakers with 50 mL of water.
2. Immerse the thermometers in the beaker and record the initial temperature of the water.
3. Add the chemical to the beaker and give it a stir. The chemical may or may not dissolve totally.
4. Monitor the temperature and record the lowest or highest temperature of that the solution reaches.


Observations

Make your predictions:

Dissolving 50 grams of compound in 50 mL of water will result in
...

ammonium nitrate, NH4NO3 a temperature rise of _____ oC
a temperature drop of _____ oC
calcium chloride, CaCl2 a temperature rise of _____ oC
a temperature drop of _____ oC
sodium chloride, NaCl a temperature rise of _____ oC
a temperature drop of _____ oC
sodium acetate, NaCH3COO a temperature rise of _____ oC
a temperature drop of _____ oC
ammonium chloride, NH4Cl a temperature rise of _____ oC
a temperature drop of _____ oC


Write down your observations for each of the chemicals:
ammonium nitrate, NH4NO3
Appearance

Initial temperature:

_________________

Final temperature:

__________________

Good candidate for hot pack or cold pack?
calcium chloride, CaCl2
Appearance

Initial temperature:

_________________

Final temperature:

__________________

Good candidate for hot pack or cold pack?
sodium chloride, NaCl
Appearance

Initial temperature:

_________________

Final temperature:

__________________

Good candidate for hot pack or cold pack?
sodium acetate, NaCH3COO
Appearance

Initial temperature:

_________________

Final temperature:

__________________

Good candidate for hot pack or cold pack?
ammonium chloride, NH4Cl
Appearance

Initial temperature:

_________________

Final temperature:

__________________

Good candidate for hot pack or cold pack?

Summary
 

Questions


1. How do cold packs work?

 

 

2. How do hot packs work?

 

 

3. How do you know that a reaction is "exothermic?"

 

 

4. How do you know that a reaction is "endothermic?"


 


5. Who uses hot packs and cold packs?

 

 

6. What is the chemical that is used in hot packs that use a super cooled fluid? Why is that chemical a good choice for use to manufacture a hot pack?

 

 

 


WWW Links
Another type of hot pack uses the science of super cooled fluids to produce heat.
Watch video Some hot packs are initiated with a metal disk inside the pouch. Click here to watch a video
(1.2MB).
Some hot packs are initiated with a metal disk inside the pouch. The liquid somehow
crystallizes and gets very warm.

Hot packs and cold packs Frequently Asked Questions
Material Safety Datasheets for this lab

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Ideas
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Key Words
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Materials
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Procedure
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Observations
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Summary
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Questions
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WWW Links

Howard Debeck Elementary School
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Phone: 604-668-6281 - Fax: 604-668-6004


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