Teacher Guide
Including Student Activities
Module 2: Illustrating Exothermic and
Endothermic Reactions
ACTIVITY GUIDE
Science @ Work II
Module 2:
Illustrating Exothermic and Endothermic Reactions
Summary:
Chemical reactions are occurring all
around us, from the changing color of the
autumn leaves, to the cooking of our food.
Muffins baked without baking powder
(NaHCO3) added are going to turn out as
flat as tortillas. Chemical reactions are
responsible for most of the energy we use
every day. The coal burned in power
plants and the gasoline burned in cars fill
our lives with activity. In a chemical
reaction, a new substance is formed when
two or more substances react. These reactions result in heat being produced or
absorbed. It is important to remember that neither of these reactions results in a
loss of energy, merely redistribution.
When watching the video, think about the glycerin and potassium permanganate
reaction and the making of ice cream. Here we have two examples: the first
being an exothermic reaction (producing heat) and the second being an
endothermic reaction (absorbing heat), reactions in both cases where energy is
being redistributed, but never lost. Endothermic and exothermic reactions
surround us everyday, from plants growing, to automobiles driving down the
road. Science is always at work around us.
Objective:
Describe the difference between endothermic and exothermic reactions and their
relationship to energy transformations, specifically the loss or production of heat.
Module 2:
Segment Length – 8:00 minutes
Science @ Work II
Module 2: Illustrating Exothermic and Endothermic Reactions
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Ohio Standards Connection:
Grade Nine Physical Science
Benchmark F:
Explain how energy may change form or be redistributed
but the total quantity of energy is conserved.
Organizer:
Nature of Matter
Indicator 16:
Illustrate that chemical reactions are either endothermic or
exothermic (e.g., cold packs, hot packs and the burning of
fossil fuels).
OSIC
Y2003.CSC.S03.G09-10.BF.L09.I16
Suggestions for the teacher:
1. Preview each segment before showing.
2. Prepare the class and gather all necessary materials.
3. Review segment content with class at each pause screen.
4. Begin “lesson sequence” activity after viewing lesson.
Safety:
Always be careful! Teachers and students should always exercise appropriate
safety precautions and utilize appropriate laboratory safety procedures and
equipment when working on science performance tasks.
Science @ Work II
Module 2: Illustrating Exothermic and Endothermic Reactions
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Activity:
Making Ice Cream – Endothermic Reaction
Materials:
• ½ cup milk
• ½ cup whipping cream
• ¼ cup sugar
• ¼ teaspoon vanilla or vanilla flavoring
• ½ to ¾ cup sodium chloride (salt) as table salt or rock salt
• 2 cups ice
• 1 quart zippered plastic bag
• 1 gallon zippered plastic bag
• thermometer
• measuring cups and spoons
• cups and spoons for eating your treat
Procedure:
1. Add ¼ cup sugar, ½ cup milk, ½ cup whipping cream, and ¼ teaspoon vanilla
to the quart zippered plastic bag. Seal the bag securely.
2. Put two cups of ice into the gallon zippered plastic bag.
3. Use a thermometer to measure and record the temperature of the ice in the
gallon bag.
4. Add ½ to ¾ cup salt (sodium chloride) to the bag of ice.
5. Place the sealed quart bag inside the gallon bag of ice and salt.
6. Seal the bag.
7. Gently rock the gallon bag from side to side. It is best to hold it by the top seal
or to have gloves or a cloth between the bag and your hands because the
bag will be cold enough to damage your skin.
8. Continue to rock the bag for 10-15 minutes or until the contents of the quart
bag have solidified into ice cream.
9. Open the gallon bag and use the thermometer to measure and record the
temperature of the ice/salt mixture.
10. Remove the quart bag, open it, and serve the contents into cups with spoons.
Science @ Work II
Module 2: Illustrating Exothermic and Endothermic Reactions
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Explanation:
Ice has to absorb energy in order to melt, changing the phase of water from a
solid to a liquid. When you use ice to cool the ingredients for ice cream, the
energy is absorbed from the ingredients and from the outside environment
including your hands, when you are holding the bag of ice. When you add salt to
the ice, it lowers the freezing point of the ice, so even more energy has to be
absorbed from the environment in order for the ice to melt. This makes the ice
colder than it was before, cold enough to freeze the ice cream. Ideally, you would
make your ice cream using 'ice cream salt', which is just salt sold as large
crystals instead of the small crystals you see in table salt. The larger crystals
take more time to dissolve in the water around the ice, which allows for evenly
distributed cooling of the ice cream, making the ice cream “creamier”.
You could use other types of salt instead of sodium chloride. Compounds that
break into two pieces upon dissolving, like NaCl breaks into Na+ and Cl -, are
better at lowering the freezing point than substances that don't separate into
particles. The more particles there are, the greater the disruption and the greater
the impact on particle-dependent properties (colligative properties) like freezing
point depression, boiling point elevation, and osmotic pressure. The salt lowers
the point at which water will re-freeze into ice; you can't add salt to very cold ice
and expect it to freeze your ice cream. This is why salt (NaCl) is not used to deice sidewalks in areas that are very cold.
Science @ Work II
Module 2: Illustrating Exothermic and Endothermic Reactions
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Quiz:
Endothermic and Exothermic Reactions
1. A solid at a temperature of 80 C is immersed into a liquid with a temperature
at 60 C.
Which statement correctly describes the energy changes between A and B?
a) Solid A releases heat and B absorbs heat.
b) Solid A absorbs heat and B releases heat.
c) Both solid A and B absorb heat.
d) Both solid A and B release heat.
Answer choice A is correct. Heat always moves from a warmer to a cooler object.
2. When ammonium chloride crystals are dissolved in water the temperature of
the water decreases. What does this temperature change indicate about the
dissolving of ammonium chloride in water?
a) It is an endothermic reaction because it absorbs heat.
b) It is an endothermic reaction because it releases heat.
c) It is an exothermic reaction because it absorbs heat.
d) It is an exothermic reaction because it releases heat.
Answer choice A is correct. In an endothermic reaction heat is being absorbed.
Science @ Work II
Module 2: Illustrating Exothermic and Endothermic Reactions
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Ohio Content Provider Recommendations:
Search String:
chemical reactions – endothermic
chemical reactions – exothermic
Additional curricular resources can be found at the following websites
using one or more of the search strings listed above to narrow your search.
INFOhio
http://www.infohio.org/
Ohio Resource Center
http://ohiorc.org/
Ohio Department of Education
http://ims.ode.state.oh.us/ODE/IMS/Lessons/
Finding Additional Resources Using D3A2:
The D3A2 helps educators analyze data, and points them to resources such as
lesson plans, assessments and activities designed specifically to address the
academic need identified by the data. In addition to linking content to data
analysis, educators will have general search capabilities to locate education
content resources aligned to the Ohio’s Academic Content Standards.
Sample D3A2 Standard Search Results:
•
•
Simple Thermodynamics of Transportation: Retrieved from the Ohio
Resource Center
o http://www.ohiorc.org/record/2310.aspx
What’s Going on with Temperature: Retrieved from the Ohio Department of
Education
o http://ims.ode.state.oh.us/ODE/IMS/Lessons/Web_Content/CSC_LP_S
03_BF_L09_I11_01.doc
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Module 2: Illustrating Exothermic and Endothermic Reactions
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