VANDERBILT STUDENT VOLUNTEERS FOR SCIENCE
http://studentorgs.vanderbilt.edu/vsvs
Endothermic and Exothermic Processes
Fall 2013
Goal: To help students understand endothermic and exothermic processes.
TN Curriculum Alignment: GLE 0807.9.3 Interpret data from an investigation to differentiate
between physical and chemical changes.
Lesson Outline:
I. Introduction
Define endothermic (heat absorbed) and exothermic (heat given off). Students will study examples of
both chemical and physical changes that are endothermic or exothermic.
II. Endothermic Physical Process
Students learn about endothermic processes by adding potassium chloride to water
III. Exothermic Physical Process
Recyclable hand warmer activity done by students.
IV. Exothermic Chemical Processes
A. Setting up the HotHands hand warmer – Activity started by students. To be left aside and returned
to in part C.
B. Anhydrous calcium chloride mixed with water –Activity done by students. Both physical and
chemical changes occur. Anhydrous calcium chloride absorbs water to become hydrated calcium
chloride, which then dissolves in water.
C. Checking the HotHands Hand Warmer – Students make observations. VSVS members explain the
chemistry behind the exothermic process.
Materials:
1 box containing 36 goggles
16 plates
8 4 oz containers of potassium chloride
8 4 oz container of calcium chloride
1 cold pack
1 ziploc bag containing:
1 4 oz bottle for a HotHands hand warmer that will be cut open in Part IVC.
1 scissors to cut open HotHands hand warmer
1 4 oz bottle containing contents of hand warmer that has been open for 24 hours
16 thermometers
8 chemical hand warmers (HotHands)
8 recyclable hand warmers (sodium acetate solution)
16 50 mL measuring cylinders
16 spoons
32 8 oz Styrofoam cups
1 trash bag for used Styrofoam cups
1 large funnel
1 waste container
16 100 ml water bottles
32 observation sheets
16 instruction sheets in sheet protectors
Note: One team member should put the following vocabulary words on the board:
endothermic, exothermic, chemical change, potassium chloride, physical change, anhydrous
calcium chloride
Another team member should fill plastic water bottles with water when you arrive and divide the
materials in the box for the various activities.
Divide students into pairs.
I. Introduction
Share the following explanation of endothermic and exothermic processes with students:
• Tell students that the word “exothermic” describes processes that give off heat.
“Ex” indicates “out of” or “giving off”, for example, exit, exhale (to breathe out), and exodus.
•
•
• “Thermic” indicates heat.
“Endothermic”, the opposite, is used for processes that absorb heat.
Heat can be given off (exothermic) or absorbed (endothermic) in both chemical and physical
changes.
Discuss the following examples:
1. Endothermic Physical Changes - (requires heat). Examples are the phase changes of ice to
water to water vapor.
Note: An important endothermic process is sweating. It helps maintain our body temperature at
normal by cooling us because the evaporation of water from our skin absorbs excess heat from our
skin.
Another physical change that usually involves absorption of heat is the process of dissolving solids
in liquids, such as water.
2. Exothermic Physical Changes: Examples are phase changes in the opposite
water vapor to water to ice release heat.
direction -
3. Endothermic Chemical changes (absorb heat) Photosynthesis is an excellent example of an
endothermic chemical reaction where the energy is supplied by the sun.
4. Exothermic Physical changes (give off heat)
An example of an application of this is the practice of spraying water on fruit trees in northern
Florida when a light freeze is expected. The water freezes on the fruit, and in the process, releases
enough heat to keep the fruit from freezing. However, this only works if the temperature doesn't drop
below about 28o F.
5. Exothermic Chemical changes (give off heat) Burning natural gas (like propane) to heat
homes is an example of an exothermic chemical change.
Your Notes:
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II. Endothermic Physical Process
Materials:
1
cold pack
16
styrofoam cups
1
trash bag for used Styrofoam cups
16
thermometers
16
50 mL measuring cylinders
8
water bottles
8
4 oz jars of potassium chloride,
8
plastic spoons (shared by pairs)
8
water bottles (shared by pairs)
32
observation sheets
16
instruction sheets in sheet protectors
Goggles
Ask students if they know what a cold pack is? When is it used?
It is a product that is used to treat muscle sprains or minor injuries.
Ask students if they know what a cold pack is made up of? Show the students a cold pack.
Activate it and pass it around the room for the students to feel. (Make sure it is returned to the
VSVS lab.)
 Share the following information with the students:
Some cold packs use the chemical ammonium nitrate. There is a plastic bag of water and a plastic bag of
ammonium nitrate inside the cold pack. The cold pack is activated by breaking the plastic divider (done
by squeezing the pack) between the water and ammonium nitrate, causing them to mix. When ammonium
nitrate dissolves in water, heat is absorbed and the packet feels cold as heat is lost.


Another endothermic reaction uses potassium chloride, KCl. In the next activity, the temperature
change will be measured during the process of dissolving potassium chloride in water.
Give each pair the following:
1 styrofoam cup
1 thermometer
1 50 mL measuring cylinder
1 water bottle (shared by two pairs)
2 observation sheets
1 instruction sheet in a protector
•
•
Give each student goggles and an observation sheet.
Distribute the 8 4 oz potassium chloride jars with 8 plastic spoons so that two pairs of students
can share them.
•
Tell each pair to:
1. Fill the 50 mL cylinders to the mark with water and pour it in the Styrofoam cup.
2. Place the thermometer in the water.
Your Notes:
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3. Record the temperature of the water on the observation sheet.
4. Add two spoonfuls of potassium chloride and stir the solution with the thermometer.
5. Record the lowest temperature reached on the observation sheet. (This takes several
minutes so students have to keep watching).
Follow Up Questions:
• Ask students what temperature difference they observed.
Write these values on the board. (Students should observe a decrease of close to 12 degrees.
• Ask students: Is this an exothermic or endothermic process? Endothermic because the
temperature decreased. The KCl absorbed heat from the water to dissolve, causing the
temperature of the water to decrease.
• Ask students: Is this a physical or chemical change? Physical because potassium chloride is
dissolving in water and can be recovered by evaporating the water
Disposal: Pour the solutions from the Styrofoam cups into the sink or the waste bottle provided.
Put used styrofoam cups in the trash bag before putting them back in the kit box.
III. Exothermic Physical Processes
Materials: 8 recyclable hand warmers
• Show the class a recyclable hand warmer that contains a supersaturated sodium acetate solution.
• Distribute 8 hand warmers to every other pair - tell students to share among two pairs.
One student in each group should bend the metal disc in the hand warmer.
•
•
•
•
•
Students should see white solid beginning to form around the button. If they don’t, they
need to bend the disc again.
Ask the students to explain what happened.
Ask students if this is an example of an endothermic or an exothermic process. Exothermic, heat
is given off.
Ask students if this is an example of a chemical or physical change. Physical, since the sodium
acetate changed from a liquid to a solid and did not form a new substance. Point out that the
hand warmer can be recycled by placing it in a pan of hot water for several minutes (directions
are given on the hand warmer).
Ask the students to explain how the recyclable hand warmer illustrates the law of conservation of
energy. This activity is a nice illustration of the energy cycle. Energy is added when the solution
is heated to form the supersaturated solution (liquid), and energy is released when crystallization
occurs.
When finished, collect all of the handwarmers and place them back in the kit box. These are reusable
(and expensive).
Your Notes:
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For VSVS Background Information: Saturated solutions contain the maximum amount of solid that
can be dissolved in a liquid at a given temperature. Usually, more solid can be dissolved if the solution
is heated to a higher temperature. However, when this solution is cooled, the excess solid crystallizes.
This is the normal process for purifying a solid by recrystallizing it from solution.
Supersaturated solutions are unstable because they contain more dissolved solid than normally can be
dissolved at that temperature. The difference between a supersaturated solution and a saturated solution
is that the excess solid doesn’t crystallize when a warm saturated solution is cooled. The excess solid
will only crystallize with the addition of a seed crystal of the same substance, or in the case of the
recyclable hand warmer, when the solution is disturbed by bending the metal disc. Only a few solids are
capable of forming supersaturated solutions. Sodium acetate trihydrate is one of them.
IV. Exothermic Chemical Processes
Materials
16 styrofoam cups
8 plastic spoons (shared by pairs)
16 50 mL measuring cylinders
8 water bottles
16 thermometers
8 HotHands hand warmers
8 4 oz jars of anhydrous calcium chloride
1 ziploc bag containing:
1 4 oz bottle with 1 HotHands hand warmer (to be cut open)
1 pair of scissors to cut open HotHands hand warmer
1 4 oz bottle containing contents of hand warmer exposed to air for 24 hours
A. Starting the Chemical (HotHands) Hand Warmer
•
•
•
•
Distribute the 8 HotHands hand warmers to every other pair and tell students to share among two
pairs.
Have one of the students tear open the plastic covering, have the group members feel the hand
warmer and note that it is at room temperature.
A group member should shake it, and put it aside until Part B.
Students should also save the plastic covering.
Note: The directions on the plastic covering suggest waiting 30 minutes, but students will be able to
feel warmth from the hand warmer after about ten minutes.
Have students go on to Part B while they are waiting for the handwarmers to get warm.
B. Anhydrous calcium chloride mixed with water
•
•
Give each pair another Styrofoam cup
Distribute 8 4-oz anhydrous calcium chloride jars with 8 plastic spoons so they can be shared by
two pairs.
Your Notes:
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Have pairs do the following:
• Measure out 50 mL of water in the measuring cylinder and add it to the cup.
• Place a thermometer in the cup, and after a few minutes, record the temperature of the water.
• Add a plastic spoonful of anhydrous calcium chloride to the styrofoam cup and stir carefully with
the thermometer.
• Record the highest temperature reading reached. This will take several minutes. (Students should
observe an increase of 20o C )
Ask students: Is this an exothermic or endothermic process? Exothermic because heat is given
off.
•
Disposal: Pour the solutions from the Styrofoam cups into the waste bottle provided. Put used
styrofoam cups in the trash bag before putting them back in the kit box. Waste solutions can be
poured down the sink at the school (preferable) or put in the white plastic bag with empty water
bottles.
•
Ask students: Is this a chemical or physical change? Accept both chemical and physical.
Anhydrous calcium chloride absorbs water to become a different chemical compound, hydrated
calcium chloride, which is a chemical change. The hydrated calcium chloride dissolves in water,
which is a physical change.
For VSVS Background Information: Both chemical and physical changes are involved since
anhydrous calcium chloride absorbs water to become hydrated calcium chloride, which then dissolves
in water. If the water is evaporated at room temperature, hydrated calcium chloride is obtained, which
has a different chemical formula, CaCl2 • 6 H2O, than anhydrous calcium chloride, CaCl2. Hydrated
calcium chloride and anhydrous calcium chloride have different properties – for example, the melting
points are different:
hydrated calcium chloride melts at 27 oC
anhydrous calcium chloride melts at 782 oC
Hydrated calcium chloride can be converted to anhydrous calcium chloride by heating it to 100 oC to
remove the water.
Tell students that anhydrous calcium chloride is used to salt roads in the winter. Calcium chloride is better
than sodium chloride for three reasons:
(1) calcium chloride gives off heat when it mixes with water
(2) calcium chloride absorbs water to become hydrated calcium chloride - this removes the
water so that there is less available to re-freeze
(3) a solution of calcium chloride has a lower freezing point than a solution of sodium chloride
because calcium chloride gives three ions per unit (CaCl2) while sodium chloride gives
only two ions per unit (NaCl) and the more ions in solution, the lower the freezing point.
Your Notes:
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Many students will be familiar with the use of rock salt to make ice cream. Rock salt is sodium chloride
and the reason it is used to make ice cream is because an ice/salt mixture has a lower temperature, about –
10o C than ice by itself. On the basis of today's experiments, calcium chloride would work even better, but
since calcium chloride is more expensive than salt, it is not used for this purpose. This difference in cost
is also why some cities use rock salt instead of anhydrous calcium chloride to melt ice on roads even
though anhydrous calcium chloride is better.
C. Checking the HotHands Hand Warmer
•
•
•
•
•
•
Have the students feel the hand warmer. (It should feel warm.)
Have students look at their observation sheet to read the list of ingredients in the Hothands
warmer. (Not all Hothands warmers will have these listed.)
• Tell the class that the “missing ingredient” that is needed to make the hand warmer warm
up is oxygen.
• When the plastic covering is removed, the inside pouch is porous enough to allow air to
enter the pouch. The oxygen in air reacts with iron to form iron oxide with the release of
heat.
Ask students if this is an example of an endothermic or exothermic process? Exothermic, heat is
released
Ask students if this is an example of a chemical or physical change. Chemical, a new substance
is formed
Take the empty 4 oz jar, cut open a hand warmer pouch and pour the contents inside the
jar. Show the students this jar and compare what the contents look like with the jar that
contains contents of a HotHands hand warmer that were exposed to air for 24 hours.
Ask students to record their observations on the observation sheet and to indicate whether a
chemical or physical change has occurred. (In the 24-hour jar, the black color of iron powder
has changed to a brownish, somewhat clumpy solid, which is iron oxide. The change in color
and characteristics of the solid are evidence for a chemical change.)
Background Information: The HotHands hand warmer is an exothermic chemical reaction that
occurs when powdered iron is mixed with activated carbon, water, salt, and vermiculite in the
presence of air. This involves the quick formation of iron oxide (activated carbon catalyzes the
reaction). The same reaction (iron + oxygen + water in the presence of salt) is the corrosion (rusting)
process, but it happens much more slowly.
•
The Hothands handwarmer cannot be recycled, because this reaction is not easily reversible.
They can be left in the classroom with the teacher or the students.
V. Review:
•
Be sure to go over the answers carefully. Students will not likely have correct responses for the
last two rows (physical and chemical changes and why) so it is important that you discuss these
and ask them to write the correct answers on their observation sheet. See answer sheet on next
page.
Your Notes:
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Lesson written by:
Dr. Melvin Joesten, Professor Emeritus, Vanderbilt University
Pat Tellinghuisen, Program Coordinator of VSVS, Vanderbilt Univers
Your Notes:
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ANSWER SHEET – SAMPLE DATA
ENDOTHERMIC/EXOTHERMIC OBSERVATION SHEET
NAME _____________________________________________________________________
Vocabulary words:
endothermic
exothermic
physical change
chemical change
potassium chloride
anhydrous calcium chloride
Ingredients in chemical hand warmer: Iron, activated carbon, water, salt, and vermiculite.
Potassium
chloride
Recyclable
Hand
warmer
Calcium
Chloride
Chemical
Hand
warmer
Temperature of Water
22 oC
-
22 oC
-
Temperature of water +
chemical
14 oC
-
37 oC or
more
-
Temperature change
- 8 oC
-
+ 15 oC or
-
more
Did it get hotter or colder?
Colder
Hotter
Hotter
Hotter
Is it Endothermic or
Exothermic?
Endothermic
Exothermic
Exothermic
Exothermic
Is it a physical or chemical
change?
Physical
Physical
Both – May
be difficult
for students
to understand
Chemical
Why?
Dissolving in
water is a
physical
change –
forms soln of
potassium
chloride
Can be
recycled by
heating to
dissolve
sodium
acetate
Explain (see
lesson)
Solid turns to
reddishbrown and
looks
different
Chemical. Anhydrous
calcium
chloride
changed to
hydrated salt
Physical –
hydrated salt
dissolves to
give soln.
ENDOTHERMIC/EXOTHERMIC OBSERVATION SHEET
NAMES _____________________________________________________________________
Vocabulary words:
endothermic
exothermic
physical change
chemical change
potassium chloride
anhydrous calcium chloride
Ingredients in chemical hand warmer: Iron, activated carbon, water, salt, and vermiculite.
Potassium
chloride +
Water
Recyclable
Hand
warmer
Calcium
Chloride
+ Water
Chemical
Hand
warmer
Temperature of Water
xxxxxxxxx
xxxxxxxx
Temperature of water + chemical
xxxxxxxxx
xxxxxxxx
Temperature change
Did it get hotter or colder?
Is it Endothermic or Exothermic?
Is it a physical or chemical change?
Why?
—
xxxxxxxxx
+
xxxxxxxx
Instruction Sheet
Endothermic and Exothermic Processes
Students work in pairs for today’s lesson.
I. Introduction
II. Endothermic Physical Process
What a cold pack is made up of?
6.
Fill the 50 mL cylinders with water and pour it in the Styrofoam cup.
7.
Place the thermometer in the water.
8.
Record the temperature of the water on the observation sheet.
9.
Add two spoonfuls of potassium chloride and stir the solution with the thermometer.
10. Record the lowest temperature reached on the observation sheet. (This takes several minutes so
keep watching).
III. Exothermic Physical Process
Recyclable Hand Warmer – share with another pair
 One of the students should firmly press and release the metal activation button or bend the metal disc
(warmers differ in their activation method).
 You should see white solid beginning to form around the disc. If you don’t, activate it again.
 What happens? Record results on your observation sheet.
IV. EXOTHERMIC CHEMICAL PROCESSES
A. Starting Chemical (HotHands)Hand Warmer – share with another pair
 Observe the hand warmer.
 When instructed to do so, tear open the plastic covering, take out the hand warmer, shake it,
and put it aside until after you do part B.
B. Anhydrous calcium chloride mixed with water
1. Fill the 50 mL cylinder with water and add it to the second, clean Styrofoam cup.
2. Measure the temperature of the water by placing the thermometer in the water and record the
temperature of the water on your observation sheet.
3. Add one spoonful of anhydrous calcium chloride.
4. Stir carefully with the thermometer
5. Record the highest temperature reached on your observation sheet. (Takes several
minutes so keep watching).
C. Checking the HotHands Hand Warmer
1. Feel the hand warmer.
2. Record your observations on the observation sheet.
3. The VSVS team will cut open a HotHands hand warmer and pour the contents
into a jar. Observe this jar and the jar that contains contents left in open air for
24 hours. Record your observations about these contents on the Observation Sheet.