Warming up or cooling down
GK-12 Inquiry Science Lesson
Eric Turner
Spring 2009
Background
This lesson explores the concepts of exothermic and endothermic reactions, and their
applications.
Key Words
Endothermic, Exothermic, Reaction
Grade Level
7-8
Objective
This lab will get students thinking about exothermic and endothermic reactions by student lead
designing of experiments to test a large variety of substances to fit a specific application. They
will also explore the properties of a commercially available hand warmer.
Safety
1. Nitrile or Latex gloves should be worn
a. Chemicals are not highly toxic, but must be treated with respect
2. Goggles should be worn
3. Aprons are optional
Arizona Content Standards
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1SC-E1: Observations, Questions, and Hypotheses - Formulate predictions, questions,
or hypotheses based on observations. Locate appropriate resources.
1SC-E2: Scientific Testing (Investigating and Modeling) - Design and conduct
controlled investigations.
1SC-E3: Analysis and Conclusions - Analyze and interpret data to explain correlations
and results; formulate new questions.
1SC-E4: Communication - Communicate results of investigations.
2SC-E1: History of Science as a Human Endeavor - Identify individual, cultural, and
technological contributions to scientific knowledge.
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3SC-E1: Science and Technology in Society - Develop viable solutions to a need or
problem
5SC-E1: Properties and Changes of Properties in Matter - Understand physical and
chemical properties of matter
Materials
At each table:
 Sodium acetate hand warmer (2 per group)
 Screw top vials containing:
o Calcium chloride
o Citric acid
o Sodium bicarbonate (baking soda)
o Ammonium nitrate
o Sodium chloride
o Vinegar
o Any other filler chemicals desired
 100 mL distilled water
 Thermometer (2 per group)
 ½ mL scoop for each chemical
 Pipette for water
 Multi well container or Styrofoam egg carton
Time
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One 70-minute class
o Depending on the amount of student led exploration allowed, can be extended to
two classes
Procedure
Review: Exothermic vs. Endothermic
o Exothermic means heat is released
 Can happen with phase changes
 Gas to liquid (condensation)
 Liquid to solid (freezing)
 Can happen with chemical reactions
 Relatively rare, must go from something ordered, to something less
ordered
o Endothermic reactions mean heat is released
 Can happen with phase changes
 Liquid to gas (evaporation)
 Solid to liquid (melting)
 Can happen with chemical reactions
 Burning candle
o The reverse of an endothermic process is exothermic, and vice versa
Hand warmers
 Sometimes the fact that freezing is exothermic is hard to visualize since ice is cold
 The hand warmers contain liquid sodium acetate
o A metal disk provides energy to begin the freezing of sodium acetate
o Freezing is an exothermic process
o Do not call them hand warmers, call them by their shape or appearance for now
 Sodium acetate is normally a solid at room temperature but needs an energy “kick” to
freeze
 Explain the situation to the class
o Have them predict whether the process will be endothermic or exothermic if the
sodium acetate freezes
 Do not let them click the metal disk
o Have them devise a method to check in groups
o Have them try to figure out how they can provide the needed energy to begin
freezing
 Allow the students to execute their plan and record their observations in groups
 How can we get the warmers back to the liquid state?
o Have students think about the opposite of exothermic
o They should conclude that energy must be put back into the warmers
o The warmers are recharged by placing them in boiling water
Application Exploration
 Present the scenario to the class:
o A worldwide shortage of sodium acetate has forced the exploration of different
chemicals to use. The company has task each group with finding different
chemicals to use and designing new hand warmers
o They also want to expand the product line to include cooling products for desert
hikers
 Review Safety Considerations
o Proper lab behavior
o Gloves
o Eye danger from UV light
 Students will need to devise a plan for testing different combinations to test for
endothermic, and exothermic reactions
 They should use quantitative methods
o Before and after temperatures are a good method
 The assignment is to find the best “hot” combination and best “cold” combination
o Should be a systematic testing method
 They must then take this information and design a product for both applications
 Groups can then present their findings to the class
o Voting can take place to determine the best product