Teko Mmolawa
Teacher’s Guide: Understanding Endothermic and Exothermic Reactions (How Hot
packs and Ice packs work)
Created for 4th and 5th grade students
Teaching Objectives:
Students will do an experiment to understand how hot packs and cold packs work. They will
be introduced to the concepts of endothermic and exothermic reactions by measuring the
changes in temperature when various substances are added to water.
Some reactions give off heat energy, while others use up heat energy and therefore appear to
be cold to the touch. Students will record the temperature of water before and after different
substances are added to it. They will then differentiate endothermic reactions from
exothermic ones based on which ones increased or decreased in temperature.
To learn about energy transfer students could also play a game called ‘grapevine’ in which
the students whisper messages to each other using cup phones. They will get to understand
that as the sound energy of their voices enters the cup it is turned into vibrations in the string
which then turns back into sound energy in the other cup.
Key Terms:
Exothermic Reaction – A chemical reaction that releases energy in the form of heat. An
increase in temperature is observed with this type of reaction.
Endothermic Reaction – A chemical reaction that uses up energy in the form of heat. A
decrease in temperature is observed with this type of reaction.
Approximate Time: 40 minutes
Materials (for a class of 20):
4 different containers to hold the mystery substances
60 grams calcium chloride
60 grams sodium acetate
60 grams baking soda
60 grams table salt
1.5 litres of water
20 cups (full size)
20 smaller cups
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Teko Mmolawa
5 thermometers
Clock or stop watch
4 graduated cylinders to measure water
Stirring rods (plastic spoons or craft sticks will do)
Safety goggles for each student
Weighing balance
Permanent marker to label cups
Cold pack and hot pack (Optional)
Procedure:
Optional demonstration: pass around a hot pack and ice pack. Have the students notice the
changes in temperature and explain that there is an exothermic and an endothermic reaction
taking place, which is why the packs feel either hot or cold.
Have students divided into 5 different groups. Each will be responsible for recording the
changes in temperature of each substance.
1. Label the different containers with mystery substances from 1 to 4.
2. Label 4 small cups and 4 big cups with the numbers 1 to 4. Each group should have a
total of 8 cups; big ones labelled 1 to 4 and small ones labelled 1 to 4.
3. Measure 50 ml of water into each of the 4 big cups.
4. Measure 15 grams of substance 1 into small cup number 1. Do the same for number 2,
3 and 4.
5. Record the initial temperature of the water. Make sure the thermometer does not touch
the bottom or the sides of the beaker. Students should look at the reading at eye level
with the thermometer to ensure accurate readings. The thermometer should be as
perpendicular as possible.
6. Add mystery substance 1 to the water. Start stirring it and begin the stop watch and
record the changes in temperature every 30 seconds for 2 minutes. Record all
findings.
7. Now add substance 2 to beaker 2. Record the temperature every 30 seconds for 2
minutes.
8. Repeat for substance 3 and 4.
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Teko Mmolawa
Mystery Substance 1
Mystery Substance 2
(Sodium
Bicarbonate/Baking
Soda)
(Sodium Chloride/
Table Salt)
Time
(min)
Temp (ºC)
Time
(min)
Temp (ºC)
Mystery
Substance 3
Mystery Substance 4
(Calcium Chloride)
(Sodium Acetate
or use crushed
alka seltzer
tables)
Time
(min)
Temp
(ºC)
Time
(min)
0
0
0
0
30s
30s
30s
30s
60s
60s
60s
60s
90s
90s
90s
90s
120s
120s
120s
120s
Temp (ºC)
As an extra exercise students could draw a simple graph with Time on the X-axis and
Temperature on the Y-axis to graphically show the changes (if any) in the temperature of the
water when the different substances were added to it.
Sources:
1.
Making Hot and Cold Packs (accessed 11th January 2012)
umanitoba.ca/outreach/crystal/resources.html
2.
Picture (accessed 10 January 2012)
http://www.coloring-pictures.net/drawings/IndianaJones/Indiana-Jones-with-hiswhip.gif
3.
Picture (accessed 10 January 2012)
http://www.colormegood.com/colormegoodPDFthumbnails/countriesandcultures/anta
rctica/penguin01.jpg
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Teko Mmolawa
Name______________________________
Indian Jones has done it again! He just broke the world record for the longest stay by any
human being in the Arctic; without a jacket or any shelter!! He threw away his cow boy hat
and boots, and wore shorts, flips flops and a visor cap and stayed in the world coldest area for
30 days and 29 nights. How is this possible?
When asked about his adventures he refused to share his secret. He only claims to have taken
a hot bath every day. One of his fans however claims to have found a mysterious white
powder on Indian Jones’ hands when he shook hands with him the day he returned from the
Arctic. What could this strange powder be? It definitely was not snow.
Human beings cannot survive too long in the Arctic without some source of heat energy to
keep their bodies warm. So we are going to explore different white powders and find out
which one he used to stay warm without a jacket, shelter or boots!
Mystery
Powder
Cup with
water
Thermometer
According to local scientists the mystery powder is supposed to produce an exothermic
reaction, which creates heat and would allow Mr Jones to stay warm for days on end. An
exothermic reaction gives off heat energy as its compounds are used up.
Instructions:
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Teko Mmolawa
1. Pour 50ml of water using a cylindrical beaker into each of your 4 cups
2. Measure out 15grams of each mystery substance using the weighing balance. Make
sure to put mystery substance 1 into cup 1, substance 2 into cup and so forth.
3. Record the temperature of the water in each cup and record it under 0seconds.
4. Add substance 1 to your first cup and record the temperature every 30 seconds for 120
seconds.
5. Do the same for substances 2, 3 and 4
Substance 1
Time
(sec)
Temp (ºC)
Substance 2
Time
(sec)
Temp (ºC)
Substance 3
Time
(sec)
Temp
(ºC)
Substance 4
Time
(sec)
0
0
0
0
30s
30s
30s
30s
60s
60s
60s
60s
90s
90s
90s
90s
120s
120s
120s
120s
Temp (ºC)
Questions:
1. Which substance’s temperature did not change a lot?
2. Which substance made the water cooler (Endothermic)? And what was the difference
in temperature between the first and final readings?
3. Which substance made the water become warmer (Exothermic)? And what was the
difference in temperature between the first and final readings?
4. Which substance do you think Indiana Jones used to keep warm in the Antarctic?
Explain why?
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