P h a s e C h a n g e I n s t r uc ti o n a l C a s e : A s er i e s o f s t u de n t -c e nt er e d s c i e nc e l es s o ns
Lesson 3
Phase Change Stations
Summary
Students will rotate to different stations observing phase changes
and recording their observations of states of matter and whether
heat is being absorbed or released. Before moving to the next
station, students place a post-it with the station number on one of
six posters each labeled with one of the following phase changes:
melting, freezing, condensation, vaporization, sublimation, or
deposition.
Objective(s)
Suggested Timeline
One to two 50-minute class periods

Students explain the different ways matter can change states.

Identify whether heat is being absorbed or released in particular
phase changes.
Materials
Teacher Background Knowledge
 9 sodium acetate heat packs (enough
for each group of 4)
 9 sticky notes for each student (one
for each lab station)
 Coconut oil
 Isopropyl “rubbing” alcohol
 Dry ice – broken into pieces
 Ice chest and newspapers for storing
dry ice
 Gloves for handling dry ice
 Ice pick or screwdriver for breaking
pieces of dry ice
 Candle
 Quarter
 Cold can and room temperature can
of soda
 4 beakers
 Popsicle sticks
 2 small trays
 4 hot plates
 2 watch glasses
 Frayer card
Phase changes can be classified as either endothermic, in which a
system absorbs energy from its surroundings, or exothermic, in
which a system releases energy to its surroundings. In each case, the
“system” is the substance undergoing the phase change. The
endothermic phase transitions are melting (solid to liquid; also
known as fusion), vaporization (liquid to gas), and sublimation (solid
to gas). In each of these transitions, energy, in the form of heat, is
going into breaking intermolecular attractions. Solids have the
strongest intermolecular attractions, followed by liquids, and then,
finally, by gases, in which intermolecular attractions are so small that
they are often ignored. The final state of the substance has weaker
attractions between the particles than the initial state. The
exothermic phase transitions are essentially the opposites of the
endothermic ones: freezing (liquid to solid), condensation (gas to
liquid), and deposition (gas to solid).
This lesson features examples of all six phase changes so that
students can compare and contrast them readily. Additionally,
students see these phase changes with substances other than water,
i.e. the freezing of wax. Students may encounter difficulties in
classifying the processes as endothermic and exothermic. This is
often because they incorrectly define the “system” in the problem.
For example, the vaporization of alcohol is an endothermic process; it
takes energy to break the intermolecular attractions between alcohol
molecules so that they can enter the vapor phase.
Frayer Card
Phase Change Instructional Case
Lesson 3
Page 2 of 5
Lesson 3
Phase Change Stations
Prior Knowledge
Teacher Background Knowledge (continued)
In grades 3-5, students have learned
that moving objects contain energy.
The faster the object moves, the more
energy it has.
When alcohol evaporates from our skin, we feel cold. That is because
we are the “surroundings”; the alcohol is the “system.” The alcohol is
absorbing energy from us, so its vaporization is endothermic.
Students often recognize endothermic processes more readily than
exothermic processes because they associate them with the
presence of a specific heat source, whereas the heat released in an
exothermic reaction is diffuse and not seen as a specific quantity. For
example, they may know vaporization as endothermic, but not think
of condensation as exothermic. Therefore, it may help to guide
students when unsure if a process is endothermic or exothermic to
try classifying the opposite process first.
Students learned in the previous
lesson that liquids and gases move
faster at higher temperatures and
solids expand. They also learn that
there is no increase in mass when
temperature increases.
Possible Modifications:
The number of stations may be
reduced, but there should be at least
one station for each of the six phase
changes. Additional optional stations
could be a “Drinking bird” apparatus
(evaporation), solid iodine
(sublimation), or distillation apparatus
(vaporization and condensation).
Prep
1. Obtain dry ice the night before or morning of and store in freezer
wrapped in newspaper. Around the room, hang posters labeled
with the following terms and descriptions: Melting (solid to
liquid), Freezing (liquid to solid), Vaporization (liquid to gas);
Condensation (gas to liquid), Sublimation (solid to gas),
Deposition (gas to solid)
2. Prepare the following stations:
Station #1 Coconut oil (melting) Place watch glass on warm
hotplate. Provide a container of coconut oil with a popsicle stick for
placing on watch glass.
Station #2 Watch glass (condensation) Place watch glass on beaker
of water on hotplate.
Station #3 Evaporating alcohol in hand (vaporization) Provide
dropper bottle of alcohol.
Station #4 Dry ice (sublimation) dry ice in tray.
Station #5 Cooling wax (freezing) Light candle, and provide popsicle
stick and paper for placing wax.
Station #6 Quarter on dry ice (deposition) Provide quarter and dry
ice in tray.
Station#7 Boiling water (vaporization) Boil water on hotplate.
Station #8 Hot pack (freezing) Provide sodium acetate hot packs,
and have hot water for “recharging” packs
Station #9 Cold soda and room temperature can of soda
(condensation) Provide can of cold soda.
3. After each class period, the sodium acetate hot packs will need to
be “recharged” (melted) by putting them in hot water on a hot
plate, removing them from the hot water, and letting them cool
for several minutes. This creates a supersaturated solution that
will turn solid (freeze) when the disk is clicked starting the
crystallization process of the dissolved sodium acetate. You
should have enough sodium acetate packets ready for each lab
team each period. Be sure to instruct students to use only one
per lab team so there are enough for all lab teams each period
4. Give each lab group 9 sticky notes.
Page 3 of 5
Lesson 3
Phase Change Stations
Standards 12
NGSS Performance Expectations:
This lesson supports students in progressing toward the NGSS Performance Expectation.
MS-PS 1-4: Develop a model that predicts and describes changes in particle motion, temperature, and
state of a pure substance when thermal energy is added or removed.
Emphasis is on qualitative molecular-level models of solids, liquids, and gases to show that adding or
removing thermal energy increases or decreases kinetic energy of the particles until a change of state
occurs. Examples of models could include drawings and diagrams. Examples of particles could include
molecules or inert atoms. Examples of pure substances could include water, carbon dioxide, and helium.
MS-PS 1-5: Develop and use a model to describe how the total number of atoms does not change in a
chemical reaction and thus mass is conserved.
Emphasis is on law of conservation of matter and on physical models or drawings, including digital forms
that represent atoms.
Assessment Boundaries: Assessment does not include the use of atomic masses, balancing symbolic equations,
or intermolecular forces.
In this lesson…
Science and Engineering Practices
Analyzing and Interpreting Data:
Analyze and interpret data to
determine similarities in findings.
Observe patterns between the
different phase changes. Analyze
and interpret data to provide
evidence for the phenomena of
phase change.
1
Disciplinary Core Ideas
Cross Cutting Concepts
PS3.A: Definitions of Energy
Cause and Effect
The term “heat” as used in
everyday language refers both to
thermal energy (the motion of
atoms or molecules within a
substance) and the transfer of
that thermal energy from one
object to another. Heat is
referred to the energy
transferred due to the
temperature difference between
two objects.
Observe the changes that occur
when different materials are
heated and cooled. Observe the
relationship between
temperature and phase change
Energy and Matter
Use the information about the
relationship of phase change
and temperature to assess
whether heat energy has been
absorbed or released. The
transfer of energy can be
tracked through each phase
change.
NGSS Lead States. 2013. Next Generation Science Standards: For States, By States. Washington, D.C.: The
National Academies Press.
2
National Governors Association Center for Best Practices, Council of Chief State School Officers Title: Common
Core State Standards (insert specific content area if you are using only one) Publisher: National Governors
Association Center for Best Practices, Council of Chief State School Officers, Washington D.C. Copyright Date: 2010
Page 4 of 5
Lesson 3
Phase Change Stations
In this lesson…
CCSS Mathematics
CCSS English-Language Arts
n/a
RST 6-8.9 Compare and contrast the information
gained from the experiments with the different
materials and substances. Compare/contrast with
information gained from reading a text on the
same topic.
Lesson
Station 1:
1. Establish connection to previous lesson i.e. “Yesterday we looked at the characteristics of solids, liquids,
and gases. Now we are going to look at what happens when changing between phases (solid, liquid, or
gas).”
2. Have students rotate between stations. They will need about 5 minutes per station to record their
observations, discuss which two states they are observing, decide which phase change they are observing
and explain their rationale. They then label their sticky notes with the station number and place the
sticky note on the appropriate poster. Sticky notes should form a bar graph on each poster, with sticky
notes of the same station number placed on top of the other.
3. After students have rotated through each station, debrief as a class. Ask for volunteers to explain why
they classified stations as they did.
Possible Questions:
 Which station(s) were the most difficult to figure out? Why?

Why do phase changes take place?

What phase changes were similar or related in some way? How?

In what phase changes was heat being released? Absorbed?
4. Hand out Frayer model cards. Complete one or two as models for the class, and have groups continue to
complete a Frayer card for each phase change process.
Page 5 of 5
Lesson 3
Phase Change Stations
Potential Pitfalls
Understand that heat (or more correctly, energy) is always absorbed or released in a phase change even
if the addition or removal of heat is not felt. The reusable sodium acetate heat packs, for example,
absorb heat when “recharged” in hot water and release heat when clicking of the metal disk initiates the
freezing process (solid sodium acetate crystals forming). Students will likely be challenged with the idea
that freezing released heat. An in-depth discussion of the observations made at different stations will be
beneficial in clarifying this for students. Example: “If melting is the opposite of freezing, and a substance
is absorbing “heat” when it melts, what happens when a substance freezes? Which station clearly
demonstrated heat being released in the freezing process? (hot packs).” Or, “Why might we not feel the
heat being released when water freezes? (there is less heat released). Why does an ice cube feel cold
when we touch it? (It is absorbing heat from our hand).”
It is important that students spend time thinking through that ice feeling cold does not contradict a
release of “heat” (energy) in the freezing process, since these are two different things. Additionally,
although scientists correctly use “heat” as a verb, we feel it is okay at this point in student understanding
to use “heat” as noun since students may not have yet been introduced to the term energy. Technically,
however, it is energy that is transferred in a phase change. Heat is a transfer of energy.