LESSON 13.4
Key Objectives
13.4.1 IDENTIFY the conditions necessary for
sublimation.
13.4 Changes of State
13.4.2 DETERMINE how the conditions at
which phases are in equilibrium are represented on
a phase diagram.
CHEMISTRY
Additional Resources
Q: Where does rain water go when a puddle dries up? Water cycles through
much of the matter on Earth. It falls as liquid rain or solid snow, collects in
rivers, oceans, or glaciers and returns to the air as a gas through evaporation. All living organisms use water and release it back into the air. Other
elements, such as carbon and nitrogen, also cycle through Earth as solids,
liquids, or gases. In this section, you will learn what conditions can control
the state of a substance.
Reading and Study Workbook, Lesson 13.4
Available Online or on Digital Media:
• Teaching Resources, Lesson 13.4 Review,
Interpreting Graphics
• Laboratory Manual, Lab 22
Key Questions
When can sublimation
occur?
How are the conditions at
which phases are in equilibrium
represented on a phase diagram?
Vocabulary
Engage
&
CHEMISTRY
Y
YO
YOU
U Explain that rain is the
condensation product of water vapor in the
atmosphere. Ask Describe the water cycle in terms
of phase changes. (Answers will vary, but responses
should focus on evaporation, condensation, and
precipitation.) Use the discussion to introduce
sublimation.
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National Science Education Standards
Sublimation
When can sublimation occur?
If you hang wet laundry on a clothesline on a very cold day, the water in the
clothes quickly freezes to ice. Eventually, however, if the day is sunny, the
clothes become dry although the ice never thaws. The ice changes directly to
water vapor without melting and passing through the liquid state. The change
of a substance from a solid to a vapor without passing through the liquid state
is called sublimation. Sublimation can occur because solids, like liquids, have
Sublimation occurs in solids with vapor pressures
a vapor pressure.
that exceed atmospheric pressure at or near room temperature.
Solid
Activate Prior Knowledge
Display in the room a large poster of the water
cycle. Use colored sticky notes to represent solids,
liquids, and gases. Have student volunteers place
the sticky notes in the correct location on the
water cycle poster. Then discuss the relationship
between temperature and the three phases of water
as an introduction to the concepts addressed in
Figure 13.18.
Y U
YO
&YOU
Gaseous I2
molecules
Solid I2
molecules
sublimation
deposition
Vapor
Iodine is another example of a substance that undergoes
sublimation. This violet-black solid ordinarily changes into a
purple vapor without passing through a liquid state. Notice in
Figure 13.15 how dark crystals of iodine deposit on the outside of a test tube placed inside another test tube. The outer test
tube contains solid iodine that is being gently heated. The inner
test tube contains liquid water and ice. The iodine crystals
at the bottom of the outer test tube change directly to iodine
vapor. When the vapor reaches the cool surface of the inner test
tube, it goes directly from the gaseous to the solid state.
Figure 13.15 Sublimation
When solid iodine is heated, the crystals
sublime, going directly from the solid to the
gaseous state. When the vapor cools, it goes
directly from the gaseous to the solid state.
436 $IBQUFSt-FTTPO
A-1, A-2, B-2, B-4, B-5, E-1, E-2
Focus on ELL
1 CONTENT AND LANGUAGE Students who know that the prefix sub- means “below
or under” may be confused by the definition of sublimation. Explain that this word
comes from the latin word sublimare which mean “to raise or elevate.”
2 FRONTLOAD THE LESSON Ask students to predict whether a solid can change to a
gas without first becoming a liquid. (Answers will vary.) Then, display a piece of dry
ice in a beaker placed in a well-ventilated area, and have students examine the beaker
for the presence of liquid (CAUTION: do not handle dry ice without appropriate
Safety precautions and gear, as it can cause serious skin damage on contact.).
Students should notice that there is no liquid in the beaker, and that the vapor
appears to come directly from the solid CO2. Explain that this type of phase change is
not limited to dry ice, and that they will explore why such a phase change is possible.
436
Chapter 13 • Lesson 4
Foundations for Reading
BUILD VOCABULARY Explain that the word sublimation
comes from the Latin word sublimare, meaning “to
elevate.” Convey that the meaning of sublimare was
expanded by the Middle Ages to include “to refine”
or purify. The process of sublimation can be used to
remove impurities from a substance.
READING STRATEGY Have students note key points
about sublimation and evaporation as they read
this lesson. Then ask them to summarize their key
points in a paragraph comparing the two processes.
Figure 13.16 Dry Ice Solid carbon dioxide, or dry
ice, sublimes at normal atmospheric pressures. As
it changes state, dry ice absorbs heat, keeping
materials nearby cool and dry.
Interpret Photos Why does fog form in the air
around the dry ice?
Explore
Sublimation
Quick Lab
Quick Lab
Purpose
Sublimation
To observe the sublimation of
air freshener
Procedure
Materials
rsmall pieces of solid air
freshener
rsmall shallow container
r2 clear 8-oz plastic cups
rhot tap water
rice
r3 thick cardboard strips
1. Place a few pieces of air freshener in
one of the cups. CAUTION Work in a wellventilated room.
2. Bend the cardboard strips and place
them over the rim of the cup that has the air
freshener pieces.
3. Place the second cup inside the first. The
base of the second cup should not touch the
air freshener. Adjust the cardboard as necessary. This assembly is your sublimator.
4. Fill the top cup with ice. Do not get any
ice or water in the bottom cup.
5. Fill the shallow container about onethird full with hot tap water.
OBJECTIVE Af
After completing this activity, students
will be able to describe the process of sublimation.
Ice
SKILLS FOCUS Observing, inferring, predicting,
communicating
PREP TIME 15 minutes
Shallow
container
with hot
water
Air freshener
6. Carefully place your sublimator in the hot water. Observe
what happens.
Analyze and Conclude
1. Define What is sublimation?
2. Predict What do you think would happen if the water in the shallow
container were at room temperature? If it were boiling?
3. Explain Why is it possible to separate the substances in some mixtures
by sublimation?
States of Matter 437
CLASS TIME 20 minutes
SAFETY Perform this activity in a well-ventilated
room. Some people are allergic to substances in air
fresheners.
TEACHING TIPS Students should not fill the shallow
containers to the point where the sublimator floats,
to prevent it from tipping over. If a colored air
freshener is used, the condensed solid will be white.
EXPECTED OUTCOME The heat from the hot water
causes the air freshener to sublime. When the
vapor reaches the cold surface of the upper cup, it
condenses back into a solid.
ANALYZE AND CONCLUDE
1.
2.
3.
Focus on ELL
The change of a substance from a solid to a gas
without passing through the liquid state.
At room temperature, there would be less
sublimation; at the boiling point, there would
be more sublimation.
When a substance sublimes in a mixture, other
components remain as residue.
FOR ENRICHMENT
4 LANGUAGE PRODUCTION Have students work in groups of four to complete the
lab. Make sure each group has ELLs of varied language proficiencies, so that more
proficient students can help less proficient ones. Have students work according
to their proficiency level.
If you used a colored air freshener, ask students to
explain why the condensed solid is white. (The dye
does not sublime and remains behind at the bottom
of the sublimator.)
BEGINNING: LOW/HIGH Rephrase each Procedure step in simple terms.
Have students follow along as you demonstrate each step.
INTERMEDIATE: LOW/HIGH Slowly read each Procedure step aloud. Answer the
Analyze and Conclude questions as a class. Have students copy the answers.
ADVANCED: LOW/HIGH Have more capable students help others with a lower
language proficiency by posing the Analyze and Conclude questions as true/false
questions.
States of Matter
437
LESSON 13.4
Sublimation has many useful applications.
If freshly brewed coffee is frozen and the water
vapor is removed with a vacuum pump (a sublimation process), the result is freeze-dried coffee. The solid carbon dioxide (dry ice) shown
in Figure 13.16 is often used as a coolant for
goods, such as ice cream, that must remain frozen during shipment. Dry ice has a low temperature of Ź78°C. Because it sublimes, it does
not produce a liquid, as ordinary ice does when
it melts. Solid air fresheners contain a variety of
substances that sublime at room temperature.
Sublimation is also useful for separating substances. Organic chemists use sublimation to
separate mixtures and to purify compounds.
How are the conditions at which phases are in equilibrium represented on a phase diagram?
Explain
Phase Diagrams
Explain
U
IRT A
The relationships among the solid, liquid, and vapor states (or phases) of a
substance in a sealed container can be represented in a single graph. The
graph is called a phase diagram. A phase diagram gives the conditions of
temperature and pressure at which a substance exists as solid, liquid, or gas
The conditions of pressure and temperature at which two
(vapor).
phases exist in equilibrium are indicated on a phase diagram by a line separating the phases.
Figure 13.18 shows the phase diagram for water. In each of the colored
regions of the phase diagram, water is in a single phase. The curving line that
separates water’s vapor phase from its liquid phase describes the equilibrium
conditions for liquid and vapor. Under these conditions, water can change its
state from liquid to vapor or from vapor to liquid. The same line also illustrates how the vapor pressure of water varies with temperature. The other
two lines describe the conditions for equilibrium between liquid water and
ice and between water vapor and ice. The point on the diagram at which all
three lines meet is called the triple point. The triple point describes the only
set of conditions at which all three phases can exist in equilibrium with one
another. For water, the triple point is a temperature of 0.016°C and a pressure
of 0.61 kPa (0.0060 atm). Figure 13.17 shows water at its triple point.
Interpret(SBQIT
L
USE VISUALS Display Figure 13.18 on an overhead
projector. Explain that a phase diagram is a
convenient way to summarize the conditions of
temperature and pressure at which the solid, liquid,
and gas phases of a substance are most stable.
Point out that each line in the diagram represents
the set of possible temperature-pressure values at
which different phases are in dynamic equilibrium
with one another. For example, in a closed system
at 100°C and 101.3 kPa, liquid water is in dynamic
equilibrium with water vapor. (Note that the
x- and y-axes are not drawn to scale so that the
triple point and normal boiling point can fit on the
graph.) Ask At what temperature and pressure
are the liquid, solid, and vapor phases of water in
dynamic equilibrium? (0.016°C, 0.61 kPa)
Figure 13.17 Triple point
This flask is at the triple point, where
ice, liquid water, and water vapor
exist in equilibrium. Freezing, melting,
boiling, and condensation are all
occuring at the same time in the flask.
LAB
Phase Diagram of Water
Pressure (kPa)
USE VISUALS Draw the phase diagram of water in
Figure 13.18 on the board. Have volunteers label the
states of matter. Using simple words, ask students
to demonstrate melting, and have a volunteer draw
an arrow on the diagram from the solid to the liquid
area. Repeat this for other changes of state.
V
LESSON 13.4
Phase Diagrams
Normal
melting
point
Normal
boiling
point
101.3
Solid
Liquid
Vapor
Extend
By this point in the course students should have
a strong understanding that reactions can occur
between different states of matter as well as
between liquids and between gases. However,
they may not realize that reactions can also occur
between solids. Explain to students that these types
of reactions produce a number of useful products,
including semi-conductors and light-sensitive
photopolymers. A number of chemists specialize in
solid-state chemistry. Have students research current
areas of experimentation in solid state chemistry
either on the Internet or by interviewing a solid-state
chemist at a local college or university, and prepare
a poster showing examples of applications of this
research that are found in everyday objects.
Triple point
0.61
0
ET
KIN IC
ART
Figure 13.18 The phase
diagram of water shows the
relationship among pressure,
temperature, and the physical
states of water. Note that the
scale on the axes is not linear.
a. Read Graphs At the
triple point of water, what are
the values of temperature and
pressure?
b. Identify What states of
matter are present at the triple
point of water?
c. Analyze Assuming
standard pressure, at what
temperature is there an
equilibrium between water
vapor and liquid water?
Between liquid water and ice?
0.016
100
Temperature (°C)
See boiling and
freezing animated
online.
Hint: Each line
represents the set of poss
ossiible
ble
temperature-pressure values
at which the different phases
are in dynamic equilibrium.
438 $IBQUFSt-FTTPO
Freeze-Dried Foods
Astronauts and backpackers use freeze-dried foods because they are lightweight and
easily reconstituted by adding water. Freeze-dried foods don’t require refrigeration
because bacteria cannot multiply in the absence of moisture. The sublimation of
ice at low pressure makes the process of freeze-drying possible. Food is frozen and
placed in a chamber attached to a vacuum pump. Then the pressure in the chamber
is lowered until the ice crystals sublime. Freeze-dried food tends to maintain its flavor
because the substances in the food that impart flavor remain in the food as the ice
sublimes.
438
Chapter 13 • Lesson 4
CHEMISTRY
Y
&YOU
Q: Describe how water might
mig
m
move from Earth’s
Earth
rth’ss surface
surfac
sur
facee to
t
Earth’s atmosphere and back
again as part of the water
cycle. Be sure to include any
phase changes that occur in
your description.
Evaluate
Informal Assessment
List a series of temperature–pressure values on the
board. Have students state or point to which phase
of water is most stable under each set of conditions
and explain why.
Reteach
On the board, draw a stoppered, sidearm flask
containing water and a chunk of ice. Note that
the sidearm is connected to a vacuum pump. Tell
students that the diagram illustrates ice, liquid
water, and water vapor in equilibrium. Have groups
of students approach the diagram and one at a
time have a student add an arrow and label to the
diagram to represent a phase change. Continue until
there are six arrows on the diagram.
PR
S
E
O
Figure 13.19 Water on Ice
The surface of ice has a thin layer
of water above it.
Apply Concepts Research shows that
the colder the ice is, the thinner the
layer of water above the ice is. In which
sports—ice hockey, speed skating or figure
skating—do you think that it would benefit
the athletes more to keep the ice colder?
NLIN
M
OBLE
&
CHEMISTRY
Y
YO
YOU
U The water in a pond
evaporates. The water vapor in the atmosphere
condenses to form clouds. When the water droplets
in clouds get heavy enough, they fall to the ground
as rain.
13.4 Lesso
LessonCheck
25.
Identify What properties must a solid have
to undergo sublimation?
29. Explain What does the triple point on a phase
diagram describe?
26.
Explain What do the curved lines on a
phase diagram represent?
30. Classify Would you expect a substance that
sublimates at or near room temperature to be a
molecular substance or an ionic substance? Use
what you learned about bonding in Chapters 7
and 8 to answer the question.
27. Apply Concepts Describe one practical use of
sublimation.
28. Interpret Graphs Using Figure 13.18, estimate
the boiling point of water at a pressure of 50 kPa.
States of Matter 439
Lesson Check Answers
25. Sublimation occurs in solids that
have vapor pressures that exceed
atmospheric pressure at or near
room temperature.
26. The lines show the conditions
of temperature and pressure
at which two phases exist in
equilibrium.
27. freeze-dried coffee, dry ice as a
coolant, air fresheners, separating
mixtures, and purifying substances
28. about 60°C
29. The triple point describes the
only set of conditions at which
three phases can exist in
equilibrium.
30. The substance is likely molecular
because the bonds between ions
are typically stronger than the
attractions between molecules.
Answers
INTERPRET GRAPHS
a. 0.016°C and 0.61 kPa
b. solid, liquid, and vapor
c.
100°C; 0°C
FIGURE 13.19 A thick layer of water means that
there is more friction, which can slow the
skaters down. In ice hockey and speed skating,
where speed is crucial, it is better to skate on
colder ice. Also, the warmer the ice is the softer
the surface of the ice is. In figure skating, the
layer of water provides a cushion for the skaters
if they fall.
States of Matter
439
LESSON 13.4
By referring to Figure 13.18, you can determine what happens if you
melt ice or boil water at pressures less than 101.3 kPa. A decrease in pressure lowers the boiling point and raises the melting point. An increase in
pressure will raise the boiling point and lower the melting point.
Look at Figure 13.18. Follow the equilibrium line between liquid water
and water vapor to the triple point. Below the triple point, the vapor and
liquid cannot exist in equilibrium. Increasing the pressure won’t change
the vapor to a liquid. The solid and the vapor are in equilibrium at temperatures below 0.016°C. With an increase in pressure, the vapor begins
to behave more like a solid. For example, it is no longer easily
compressed.
Figure 13.18 also illustrates how an increase in pressure
affects the melting point of ice. For years, the accepted
hypothesis for how ice skaters move along the ice
was the following. The blades of the skates exert
pressure, which lowers the melting point of the
ice. The ice melts and a film of water forms
under the blades of the skates. This film acts
as a lubricant, enabling the skaters to glide
gracefully over the ice as shown in Figure 13.19.
This hypothesis fails to explain why skiers also glide along very
nicely on another solid form of water—snow. Wide skis exert
much less pressure per unit area of snow than narrow skate
blades exert on ice. Recent research shows that the surface of
ice has a slippery, water-like surface layer that exists well below
ice’s melting point. Even ice that is at Ź129°C has this layer. A
new hypothesis proposes that the liquid-like surface layer provides the lubrication needed for smooth skating and skiing.
CHEMISTRY & YOU
CHEMISTRY
Y
&
CHEMISTRY
Y
YO
YOU
U Hazardous wastes such
as chemicals and medical items (biological fluids and
tissues, syringe needles, and so on) are often buried
in landfills or incinerated in traditional hightemperature incinerators. Both methods are
effective, but have some serious disadvantages.
For example, landfills rely on bacterial decomposition
to destroy hazards. However, this requires time, and
some chemicals do not undergo biological
decomposition. Landfills also can leak, contaminating
groundwater. High-temperature incinerators rely on
combustion to destroy hazardous wastes, but must
consistently reach temperatures greater than 1200°C
to break chemical bonds. At lower temperatures,
incomplete combustion or the formation of
hazardous by-products may occur. Incomplete
combustion results in soot formation. It may also
take several hours for solid wastes to be completely
incinerated.
Pose the following question to students: Based on
the description given in the feature, what are some
benefits of using a plasma waste converter instead
of burning waste material?
You may need to guide students in the following
ways:
• The temperature in a plasma furnace can be
hotter than the surface of the Sun, which is
5497°C.
• Plasma furnaces are enclosed, unlike incinerators
where waste is burned.
• Some high-temperature incinerators produce
liquid waste that must be treated before it can be
discharged into the sewer system.
Explain
START A CONVERSATION Engage students in
discussing how a plasma is different from other
states of matter. They should understand that,
unlike other states of matter, a plasma is not made
of neutral atoms. The particles of a plasma have
so much energy that the electrons are stripped
away, leaving positively charged ions and negatively
charged electrons. Point out that, although other
states of matter are more common on Earth, plasma
is the most common state of matter in the universe.
Stars, including our Sun, are made of plasma.
Y U: GREEN
YO
G
CHEMISTRY
&YOU:
Plasma Waste Converter
You are very familiar with solids, liquids, and gases, but did you know that there’s a fourth state of
matter called plasma? A plasma is a gaseous mixture of freely moving positive ions and electrons.
Plasmas exist naturally in the sun and other stars, and in lightning. Plasmas can also be artificially
created and used in a variety of technologies. One new application of plasma technology is plasma
waste converters, which treat most waste material, including many hazardous wastes.
Plasma waste converters produce plasmas with temperatures as high as 7,000°C. The energy
within the plasma breaks the waste material’s molecular bonds so that the material separates into
its elemental components. The end products are a hydrogen-rich gas known as syngas and a solid
known as slag.
Plasma waste converters have many benefits over traditional waste treatments. They do
not require the use of dumps or landfills, and they emit much less greenhouse gases and other
pollutants than incinerators. Despite these benefits there are currently only two plasma waste
treatment plants that process municipal solid waste. This is mostly due to the cost since each plant
must be custom-built. Standardizing production should result in the construction of more plants.
Torch
Plasma
SYNGAS
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SLAG
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PLASMA FURNACE 5IFQMBTNBUPSDIFTUVSOUSBTIJOUP
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440 $IBQUFSt$IFNJTUSZ:PV
21st Century Learning To be successful in the 21st century, students
need skills and learning experiences that extend beyond subject matter mastery. The
following project helps students build the following 21st Century Skills: Creativity and
Innovation; Communication and Collaboration; Information Literacy; Initiative and
Self-Direction.
USING PLASMA Pose the following challenge to your students. Suppose you are
the Safety supervisor for a welding company. It is your responsibility to train new
welders about workplace Safety in regards to plasma welding equipment. Create a
multimedia presentation on workplace Safety with regards to handling and using
plasma welding equipment that includes a 15-20 minute computerized slide show
and a take-home brochure.
The presentation and brochure should explain the chemical and physical properties
of plasma, why plasma it is used for welding, its advantages and disadvantages
compared to other types of welding, and include all Safety considerations.
440
Chapter 13 • Chemistry & You
of a plasma furnace and think about its different
parts. Ask Why do you think the trash is shredded?
(to make breaking it down easier) Ask How is
the syngas (synthetic gas, pronounced sin gas)
separated from the slag? (The less-dense gas moves
upward, and the denser slag flows out.) Ask Why
do you think the slag in the photo forms a glass
rather than crystals? (Like volcanic rocks, the slag
cools so quickly that the particles do not have time
to arrange themselves into a repeating pattern
before the slag hardens.)
Extend
FROM THE FURNACE TO THE GRID
The extremely hot syngas can heat
water to produce steam that turns
turbines producing electricity. Some
of this electricity is used to power
the plant while the rest of it is sold
to the power grid.
Connect to
ECONOMICS
Encourage students to consider whether a plasma
waste converter ultimately has a higher or lower
cost for society. Point out that although a plasma
waste converter is expensive to build, the costs of
not building it might be high also. For example, have
students consider the costs to society of dealing with
polluted air and storing toxic wastes such as PCBs.
FILL ‘ER UP
The hydrogen-rich syngas can
be used as a fuel source in
fuel cell-powered vehicles.
SELLABLE SLAG
Air-cooled slag forms
black, glassy rocks.
These rocks can
be sold and used
to make concrete
or asphalt.
Take It Further
1. Infer Describe how a gas might become a plasma.
2. Compare and Contrast Is it misleading to refer to a plasma
waste converter as a plasma incinerator? Research how incinerators
work and compare them to how plasma waste converters work.
3. Evaluate the Impact on Society How might the use of plasma
waste converters change society?
Chemistry & You 441
Answers
Differentiated Instruction
TAKE IT FURTHER
1.
L1
STRUGGLING STUDENTS Have students study the feature with a partner. Instruct
students to read each paragraph and discuss it before going to the next paragraph.
Check with pairs frequently to provide guidance and answer questions.
2.
ELL ENGLISH LANGUAGE LEARNERS List idiomatic and unfamiliar words in the
feature on the board. For example, you might list municipal, the grid, sellable,
molten, fill ‘er up, concrete, and asphalt. Discuss their meanings before students
attempt to read the feature.
L3 ADVANCED STUDENTS Have students research a municipal plasma waste
conversion facility that exists today, or one that is being planned or built. Instruct
students to provide a short summary for the class about the facility.
3.
Heat a gas until electrons begin to strip off the
atoms.
Yes, it is misleading to refer to a plasma waste
converter as a plasma incinerator because
a plasma waste converter does not burn
waste. Rather it breaks the waste down into
its elemental components. Furthermore, a
byproduct of incineration is ash. Ash must still
be disposed of in landfills.
Less green space would have to be set aside for
landfills. There may not be the need to recycle.
Also, plasma waster converters could reduce
society’s dependence on fossil fuels.
Chemistry & You
441
CHEMISTRY & YOU
USE VISUALS Have students study the diagram