13
States of M
Matter
Planning G
Guide
Introducing the
BIGIDEA:
KINETIC THEORY
The w
Th
ways iin whi
which
h particle
ti l motions
ti
vary with changes
h
in temperature an
and pressure determine whether a substance will be a solid, liquid, or gas.
NSES
Lessons and Objectives
Print Resources
For the Student
For the Teacher
A1, A-2, B-2,
B-5
13.1
The Nature of Gases p 420–424
13.1.1 List the three assumptions of the kinetic
theory as it applies to gases.
13.1.2 Interpret gas pressure in terms of kinetic
theory.
13.1.3 Define the relationship between the
temperature in kelvins and the average
kinetic energy of particles.
Reading and Study
Workbook Lesson 13.1
Lesson Assessment 13.1
p 424
Teaching Resources, Lesson 13.1
Review
Teacher Demo, p 421: Elastic
Collisions
Teacher Demo, p 422: Air
Pressure
Class Activity, p 423: Kinetic
Energy and Frequency of
Collision
A-2, B-2, B-5
13.2 The Nature of Liquids p 425–430
13.2.1 Identify the factors that determine physical
properties of a liquid.
13.2.2 Define evaporation in terms of kinetic
energy.
13.2.3 Define the conditions under which a
dynamic equilibrium can exist between a
liquid and its vapor.
13.2.4 Identify the conditions under which boiling
occurs.
Reading and Study
Workbook Lesson 13.2
Lesson Assessment 13.2
p 430
Teaching Resources,
Lesson 13.2 Review
Teacher Demo, p 427: Vapor
Pressure
Teacher Demo, p 428:
Comparing Vapor Pressures
of Water and Alcohol
Class Activity, p 429:
Temperature and Boiling
A-1, A-2, B-2,
B-3, E-2, G-1
13.3 The Nature of Solids p 431–434
13.3.1 Describe how the structure and properties
of solids are related.
13.3.2 Identify the factors that determine the
shape of a crystal.
Reading and Study
Workbook Lesson 13.3
Lesson Assessment 13.3
p 434
Small-Scale Lab: The
Behavior of Liquids and
Solids, p 435
Teaching Resources, Lesson
13.3 Review
Class Activity, p 432:
Wallpaper Lattices
Teacher Demo, p 433:
Crystalline Solid Model
A-1, A-2, B-2,
B-3, E-2, G-1
13.4 Changes of State p 436–439
13.4.1 Identify the conditions necessary for
sublimation.
13.4.2 Determine how the conditions at which
phases are in equilibrium are represented
on a phase diagram.
Reading and Study
Workbook Lesson 13.4
Lesson Assessment 13.4
p 439
Quick Lab: Sublimation,
p 437
Teaching Resources, Lesson
13.4 Review
Assessing the
BIGIDEA:
KINETIC THEORY
Essential Questions
1
1. What factors determine the physical state of a
substance?
2. What are the characteristics that distinguish
gases, liquids, and solids?
3. How do substances change from one state to
another?
418A Chapter 13
Study Guide
Gu
p 442
STP p 447
Reading and Study
Workbook Self-Check
and Vocabulary Review
Chapter 13
Materials List
FFor the
h S
Student
d
Digital Resources
Editable Worksheets
PearsonChem.com
L
ESSON
W
OV
ERVIE
CHEM
TU
TOR
13.1 Lesson Overview
Converting Between
Units of Pressure
Small-Scale Lab, p 435
• plastic Petri dish
• water
• ice
• rubbing alcohol
• calcium chloride
• graph paper (1-cm cycle)
• bromothymol blue solution
• vinegar
• aqueous ammonia
Quick Lab, p 437
• small pieces of solid air
freshener
• small shallow container
• 2 clear plastic cups
(8 oz each)
• hot tap water
• ice
• 3 thick cardboard strips
For the Teacher
L
W
ERVIE
ET
KIN IC
ART
L
ESSON
W
OV
Lab 21: Allotropic Forms of Sulfur
OV
Small-Scale Lab Manual Lab
Lab 20: Absorption of Water
by Paper Towels:
A Consumer Lab
ESSON
N
ACTI
O
IN
L
ESSON
W
OV
Lab 22: Changes of Physical State
Lab Practical 13-1: Changes of
Physical State
NCEP
TS
CO
ERVIE
ERVIE
ET
KIN IC
ART
Teacher Demo, p 421
• Newtonian cradle
13.2 Lesson Overview
Evaporation
13.3 Lesson Overview
Crystal Structures of
Solids
13.4 Lesson Overview
Change of State
Teacher Demo, p 422
• empty aluminum beverage
can
• water
• hot plate
• foil or other material for
sealing opening of can
Class Activity, p 423
• cardboard containers
(such as half-pint milk
cartons)
• ball bearings
Teacher Demo, p 427
• manometer
• 1-L flask with 2-hole
stopper
• separatory funnel
• short piece of glass tubing
bent at a 90° angle
• rubber hose
• 50 mL acetone
• ice water
Teacher Demo, p 428
• 2 cotton balls
• water
• rubbing alcohol
Class Activity, p 429
• thermometer
• beaker
• water
• ring stand
• thermometer clamp
• hot plate
Class Activity, p 432
• samples of wallpaper with
repeating patterns
Teacher Demo, p 433
• dishwashing detergent
• watch glass
• overhead projector
• drinking straw
Additional Digital Resources
S
PR
M
OBLE
MATH
TU
TOR
U
IRT A
V
Chapter 13 Problem Set
L
NLIN
E
Exam View Assessment Suite
Classroom Resources Disc
(includes editable worksheets)
• Lesson Reviews
• Practice Problems
• Interpret Graphs
• Vocabulary Review
• Chapter Quizzes and Tests
• Lab Record Sheets
O
Online Student Edition
Online Teacher’s Edition
LAB
The Effect of NaCl on the Boiling and Freezing Points
of Water
Reading Graphs
States of Matter 418B
TU
TOR
L
V
IRTUA
MATH HELP Identify the students that
struggle with math by assigning an online
math skills diagnostic test. These students
can then improve and practice math skills
using the MathXL tutorial system.
VIRTUAL LAB Students go on an animated
INSIDE:
t13.1 5IF/BUVSFPG(BTFT
t13.2 5IF/BUVSFPG-JRVJET
t13.3 5IF/BUVSFPG4PMJET
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LAB
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NLIN
CHEM
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IN
ACTI
TOR
E
ART
PR
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IRTUA
ACTI
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IN
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t13.4 $IBOHFTPG4UBUF
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KI IC
Hot, liquid lava flows from a
volcano. When it cools to a
solid, new rock will be formed.
key problem-solving skills in an online
problem set.
virtual lab tour in which the effect of
sodium chloride on the boiling and freezing
points of water is studied in a simulated
laboratory environment.
LAB
States of Matter
V
MATH
PROBLEM SETS Students can practice
13
S
S
M
O BL E
step-by-step tutorials for solving problems
involving conversions between units of
pressure.
O
NLIN
E
O
TOR
CHEM TUTOR Students access guided,
O BL E
M
CHEM
TU
PR
CHAPTER 13
What’s Online
TU
TOR
KINETIC ART Students watch animations of
selected figures from the chapter followed
by questions to check for understanding.
CONCEPTS IN ACTION Students watch an
overview of a key chapter concept using
real-world contexts and concrete examples
and analogies. Each activity includes an
interactive animation followed by analysis
questions.
National Science Education Standards
418
A-1, A-2, B-2, B-4, B-5, E-1, E-2
Focus on ELL
1 CONTENT AND LANGUAGE Have students follow along as you read the lesson
titles and Essential Questions out loud. Then write the word nature on the board and
explain that it has many meanings. Have students use the lesson titles and Essential
Questions to formulate their own definition of nature as it is used in the lesson titles.
BEGINNING: LOW/HIGH If literate, translate the lesson titles and Essential Questions
into students’ native language. Provide students with a simplified English definition
of the term nature.
INTERMEDIATE: LOW/HIGH Have students use context clues in the lesson titles and
Essential Questions to develop their own definition for the term nature.
ADVANCED: LOW/HIGH Have students look up the definitions of the term nature
418
Chapter 13
in the dictionary. Have them use context clues from the lesson titles and Essential
Questions to determine which definition is best suited for the term in this context.
KINETIC THEORY
Essential Questions:
1. What factors determine the physical
state of a substance?
2. What are the characteristics that
distinguish gases, liquids, and solids?
3. How do substances change from one
state to another?
CHEMYSTERY
Foggy Car
Windows
It’s a cold, rainy day
in September, and you
and a friend are heading
out to a movie. When you
u first
get into your mom’s car, you can clearly see
nearby trees swaying in the wind. But shortly
after your mom starts the car, the glass fogs
up, making it almost impossible to see outside.
Your mom sighs, and turns on the heat, which
only makes the foggy windows worse. Then
she turns on the air conditioner, and the fog
is gone in seconds. Why do car windows fog
up when it is cold or raining outside? Why
does the fog go away when you turn on the air
conditioner?
Connect to the BIGIDEA As you read
about states of matter, think about what might
cause car windows to fog.
NATIONAL SCIENCE EDUCATION STANDARDS
A-1, A-2, B-2, B4, B-5, E-1, E-2
Understanding By Design
Students are building toward understanding states
of matter by relating them to the kinetic theory
of matter.
PERFORMANCE GOALS At the end of Chapter 13,
students will be able to answer the essential
questions by applying their knowledge of states
of matter. Students will also be able to convert
between different units of pressure.
ESSENTIAL QUESTIONS Read the essential questions
aloud. Ask Why are solids, liquids, and gases
called physical states and not chemical states? (If a
substance changes from one state to another, only
its physical properties change. It still has the same
chemical makeup.) Ask Is the temperature at which
a substance changes from one state to another
always the same? Explain. (No. The temperature at
which a substance changes state depends on both
temperature and pressure.)
Use the photo of a lava flow to help
students connect to the concepts
they will learn in this chapter. Activate prior
knowledge by discussing the properties of the lava.
Ask What are the two states of matter you can see
in the photo? (solid and liquid) Ask How are the
properties of the solid and liquid lava different?
(The solid is hard, cannot flow, and has a fixed
shape. The liquid is not hard and can flow. Its shape
changes and it is hotter than the solid.)
BIGIDEA
Have students read over the
CHEMystery. Connect the
CHEMystery to the Big Idea of Kinetic Theory by
explaining that the state of matter depends on how
the particles of a substance move. Ask students to
predict why the fog on the car windows goes away
when the air conditioner is turned on. As a hint,
suggest that students think about how much water
the air can hold at different temperatures.
CHEMYSTERY
Introduce the Chapter
IDENTIFYING PRECONCEPTIONS Students may have not have considered that
substances can change from one state to another at temperatures other than their
boiling points and melting points, and that these points can vary. Use the activities
to introduce these concepts.
Activity 1 You will need pea-sized bits of dry ice, a beaker with water, insulated
gloves, and tongs. As students watch, use tongs to drop bits of dry ice into the water.
Students will see the bits swirl as the dry ice becomes warmer and forms carbon
dioxide gas. Explain that the solid is changing to a gas by sublimation.
Activity 2 Ask At what temperature does liquid water change to water vapor?
(Students may say 100ºC.) Point out that water also changes to a gas by evaporation
at any temperature. Have students slightly dampen a sheet of paper and observe it
after a day. The paper will be dry because the water evaporated.
States of Matter
419
CHAPTER 13
BIGIDEA
LESSON 13.1
Key Objectives
13.1.1 DESCRIBE the three assumptions of the
kinetic theory as it applies to gases.
13.1.2 INTERPRET gas pressure in terms of
kinetic theory.
13.1.3 DEFINE the relationship between the
temperature in kelvins and the average kinetic
energy of particles.
13.1 The Nature of Gases
CHEMISTRY
Y U
YO
&YOU
Q: What factors most strongly affect the weather? The atmosphere is a gas,
and the factors that determine the behavior of gases—temperature and pressure—affect the weather in the atmosphere. That is why weather maps show
temperature readings and areas of high and low pressure. In this lesson, you
will learn how temperature and pressure affect the particles of a gas.
Additional Resources
Reading and Study Workbook, Lesson 13.1
Available Online or on Digital Media:
• Teaching Resources, Lesson 13.1 Review
Key Questions
What are the three
assumptions of the kinetic
theory as it applies to gases?
How does kinetic theory
explain gas pressure?
Engage
&
CHEMISTRY
Y
YO
YOU
U Display a weather map
from your local paper and explain what the symbols
represent. Ask student volunteers to interpret the map
and predict the weather for the week. Ask What type
of weather can you expect if the map shows a dry,
cold air mass moving into your area during the
summer? (cool temperatures, dry air, and clear skies)
Explain that winds often blow from areas of high
pressure towards areas of low pressure. Ask What
causes pockets of air in Earth’s atmosphere to have
different pressures? (uneven heating of Earth’s surface)
National Science Education Standards
What is the relationship
between the temperature in
kelvins and the average kinetic
energy of particles?
Vocabulary
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Kinetic Theory and a Model for Gases
What are the three assumptions of the kinetic theory as it applies
to gases?
The word kinetic refers to motion. The energy an object has because of its
motion is called kinetic energy. According to the kinetic theory, all matter
consists of tiny particles that are in constant motion. The particles in a gas are
usually molecules or atoms. The kinetic theory as it applies to gases includes
the following fundamental assumptions about gases.
The particles in a gas are considered to be small, hard spheres
with an insignificant volume. Within a gas, the particles are relatively far
apart compared with the distance between particles in a liquid or solid.
Between the particles, there is empty space. No attractive or repulsive forces
exist between the particles.
The motion of the particles in a gas is rapid, constant, and random. As a result, gases fill their containers regardless of the shape and
volume of the containers. An uncontained gas can spread out into space
without limit. The particles travel in straight-line paths until they collide with
another particle, or another object, such as the wall of their container. The
particles change direction only when they rebound from collisions with one
another or with other objects.
Measurements indicate that the average speed of oxygen molecules in
air at 20°C is an amazing 1700 km/h! At these high speeds, the odor from a
hot cheese pizza in Washington, D.C., should reach Mexico City in about 115
minutes. That does not happen, however, because the molecules responsible
for the odor are constantly striking molecules in air and rebounding in other
directions. Their path of uninterrupted travel in a straight line is very short.
The aimless path the molecules take is called a random walk.
All collisions between particles in a gas are perfectly elastic.
During an elastic collision, kinetic energy is transferred without loss from one
particle to another, and the total kinetic energy remains constant. The
diagrams in Figure 13.1 illustrate the assumptions of kinetic theory as applied
to gases.
420 $IBQUFSt-FTTPO
B-2, B-4, B-5
Focus on ELL
1 CONTENT AND LANGUAGE Assign small groups one content vocabulary term.
Groups should prepare a learning tool for the class. This tool should show how to
pronounce the assigned vocabulary term and provide a meaning for it. Encourage
groups to use word-analysis strategies, pronunciation spelling, vowel patterning,
sounds-like clues, and illustrations. Groups should present their learning tool to the class
and address common misinterpretations and mispronunciations of their assigned word
2 FRONTLOAD THE LESSON Engage students in a discussion of what they already
know about gases. Discuss why the intensity of odors vary depending on proximity to
the source. Discuss the danger of odorless gases, such as carbon monoxide. Finally,
point out that gasoline used in cars is often referred to as gas, but it is actually a liquid.
3 COMPREHENSIBLE INPUT Use Figure 13.1 to introduce properties of gases. Explain
420
Chapter 13 • Lesson 1
that by considering the small scale action of individual gas particles students can get
a sense of the large scale action of a gas.
b
c
Explain
Bromine
molecule
Br2
vapor
Kinetic Theory and a Model
for Gases
USE VISUALS Direct students to Figure 13.1. Be
Figure 13.1 Characteristics of Gases
Gases share some common characteristics.
a. The rapid, constant motion of particles in a gas causes them to collide with
one another and with the walls of their container. b. The particles travel in straight-line
paths between collisions. c. A gas fills all the available space in its container.
Relate Cause and Effect Why don’t the particles in a gas eventually slow down and stop?
sure students understand that the space between
the gas particles is not filled with air or any other
substance. Help students visualize that the pressure
of a gas is caused by collisions of the particles
with the walls of the container; point out that the
magnitude of the pressure is related to how often
and how hard the particles strike the walls.
Gas Pressure
Explore
How does kinetic theory explain gas pressure?
A balloon filled with helium or hot air maintains its shape because of the
pressure of the gas within it. Gas pressure results from the force exerted by
a gas per unit surface area of an object. What causes this force? Moving bodies exert a force when they collide with other bodies. Although a single partiFigure 13.2 Atmospheric Pressure
cle in a gas is a moving body, the force it exerts is extremely small. Yet it is not
At sea level, air exerts enough
hard to imagine that simultaneous collisions involving many particles would
pressure to support a 760-mm
Gas pressure is the result of
produce a measurable force on an object.
column of mercury. On top of Mount
billions of rapidly moving particles in a gas simultaneously colliding with
Everest, at 9000 m, the air exerts
an object. If no particles are present, no collisions can occur. Consequently,
only enough pressure to support a
there is no pressure. An empty space with no particles and no pressure is
253-mm column of mercury.
called a vacuum.
You are already familiar with a gas pressure
caused by a mixture of gases—air. Air exerts presVacuum
sure on Earth because gravity holds the particles
in air within Earth’s atmosphere. The collisions
of atoms and molecules in air with objects results
in atmospheric pressure. Atmospheric pressure
Atmospheric
decreases as you climb a mountain because the denpressure
760
mm
Hg
sity of Earth’s atmosphere decreases as the elevation
(barometric
increases.
pressure)
A barometer is a device that is used to measure
253 mm Hg
atmospheric pressure. Figure 13.2 shows an early
type of mercury barometer. The height of the mercury column in the tube depends on the pressure
exerted by particles in air colliding with the surface
of the mercury in the dish. Atmospheric pressure
depends on weather and on altitude. In fair weather
at sea level, the atmospheric pressure is sufficient to
support a mercury column 760 mm high.
Sea level
On top of Mount Everest
States of Matter 421
Differentiated Instruction
ELL
ENGLISH LANGUAGE LEARNERS Have available the weather section of the local
newspaper, and the weather reports from students’ native cities. Help students determine
the day’s pressure, in all locations, in units of mm Hg, kPa, and atm, and to compare
data. Students may wish to track the daily pressure and display the changes on a graph.
L1 STRUGGLING STUDENTS To help convey the meaning of the word kinetic, show
a video of kinetic sculptures created by sculptor Theo Jansen. Challenge students to
create a kinetic sculpture that reflects the concepts in this lesson.
L3
ADVANCED STUDENTS Unlike traditional barometers, aneroid barometers do not
balance atmospheric pressure against a liquid of known density. In fact, they contain
no liquid and are independent of gravity. If possible, bring one to class and explain its
components. Have interested students research the advantages of aneroid barometers.
(They are compact, self enclosed, and easily transported. They can operate under
conditions not suited to mercury barometers.)
Gas Pressure
Teacher Demo
PURPOSE Students will observe and differentiate
elastic collisions from perfectly elastic collisions.
MATERIALS Newtonian cradle (a device in which
small steel balls are suspended by thin nylon tethers
to horizontal wooden sticks)
PROCEDURE Explain that in an elastic collision,
kinetic energy is transferred between the objects
that collide. In a perfectly elastic collision, the total
amount of kinetic energy remains constant. Then
pull back one of the balls and let it fall into the
other balls. Let the balls come to rest. Ask Were the
collisions between the balls elastic? (Yes, because
kinetic energy was transferred with each collision.)
Ask Why did the balls eventually stop moving? (The
collisions were not perfectly elastic; some kinetic
energy was lost as heat during each collision.)
Remind students that the kinetic theory assumes
that all collisions between particles in a gas are
perfectly elastic. (Note: In Chapter 14, students will
learn that the assumptions of the kinetic theory do
not hold true for real gases under all conditions.)
Explain
USE VISUALS Direct students to Figure 13.2. Point
out the parts of the barometer and explain how the
barometer is used to measure atmospheric pressure.
Ask What is the decrease in pressure from sea level
to the top of Mount Everest in kPa? (507 mm Hg)
Answers
FIGURE 13.1 The particles in a gas collide elastically
meaning that the total amount of kinetic
energy remains constant, and the particles
do not slow down and stop.
States of Matter
421
LESSON 13.1
a
LESSON 13.1
CHEMISTRY
Explore
Gas Pressure
&
CHEMISTRY
Y
YO
YOU
U The height of the
mercury column in a barometer decreases as a storm
approaches because the atmospheric pressure
decreases
Sample Practice Problem
A.
B.
What pressure, in mm Hg and atm, does a
sample of neon gas exert at 75.0 kPa? (563 mm
Hg, 0.740 atm)
What pressure, in mm Hg and kPa, does a
sample of argon gas exert at 1.561 atm? (1186
mm Hg, 158.1 kPa)
Explore
Teacher Demo
PURPOSE Students will become aware of the
&YYOU
Q: When weather forecasters
state that a low-pressure system
is moving into your region, it
usually means that a storm is
coming. What do you think
happens to the column of
mercury in a barometer as a
storm approaches? Why?
CHEM
TU
TOR
The SI unit of pressure is the pascal (Pa). It represents a very small
amount of pressure. For example, normal atmospheric pressure is about
100,000 Pa, that is, 100 kilopascals (kPa). Two older units of pressure are still
commonly used. These units are millimeters of mercury (mm Hg) and atmospheres. One standard atmosphere (atm) is the pressure required to support
760 mm of mercury in a mercury barometer at 25°C. The numerical relationship among the three units is
1 atmâ760 mm Hgâ101.3 kPa
When studying gases, it is important to be able to relate measured values
to standards. Recall that the standard temperature and pressure (STP) are
defined as a temperature of 0°C and a pressure of 101.3 kPa, or 1 atm.
Sample1SPCMFN13.1
Converting Between Units of Pressure
A pressure gauge records a pressure of 450 kPa.
Convert this measurement to
a. atmospheres.
b. millimeters of mercury.
— Analyze List the knowns and the unknowns. The given
pressure is converted into the desired unit by multiplying by
the proper conversion factor.
˜Calculate
KNOWNS
pressure ä450 kPa
1 atm ä101.3 kPa
1 atm ä760 mm Hg
UNKNOWNS
pressure äatm
pressure ämm Hg
Solve for the unknowns.
1atm
101.3 kPa
Identify the appropriate conversion
factor to convert kPa to atm.
a.
Multiply the given pressure by the
conversion factor.
450 kPaò
Identify the appropriate conversion
factor to convert kPa to mm Hg.
b.
Multiply the given pressure by the
conversion factor.
450 kPaò
tremendous pressure exerted by Earth’s atmosphere.
MATERIALS empty aluminum beverage can, water,
hot plate, foil or other material for sealing opening
of can
PROCEDURE Explain to students that they live at
the bottom of a very deep “ocean” of air. Fill an
empty aluminum beverage container with water to
a depth of about 1 to 2 cm. Set the can on a hot
plate and bring the water to a boil. Allow the water
to boil vigorously for several minutes. Remove the
can from the heat source, seal the opening, and
allow the can to cool at room temperature or invert
the can in a pan of cool water.
EXPECTED OUTCOME Once the water vapor inside
the can condenses, the atmospheric pressure
will crush the can. Ask students to interpret their
observations.
1atm
ä4.4 atm
101.3 kPa
760 mm Hg
101.3 kPa
760 mm Hg
ä3400 mm Hgä3.4ò103 mm Hg
101.3 kPa
™Evaluate
Do the results make sense? Because the first conversion factor is much less
than 1 and the second is much greater than 1, it makes sense that the values expressed in
atm and mm Hg are respectively smaller and larger than the value expressed in kPa.
1. What pressure, in kilopascals and in atmospheres, does a gas exert at 385 mm Hg?
2. The pressure at the top of Mount Everest is
33.7 kPa. Is that pressure greater or less than
0.25 atm?
422 $IBQUFSt-FTTPO
Foundations for Math
CHECKING ANSWERS Remind students that scientists check their answers when
making conversions to be sure they are reasonable. This is an especially important
step when working with measurements that can be converted between more than
one acceptable unit of measurement.
In Sample Problem 13.1, answers are evaluated in relation to the conversion factor
used for each calculation. For part a, 450 kPa is being divided by a value of just over
100, so it is reasonable to expect a value approximately equal to 4.5 atm. In part b,
450 kPa is being multiplied by a factor of approximately 7.6. Because 7.6 rounds to
8, it is reasonable to expect an answer of approximately 3600 mm Hg. The actual
answer, 3.4 × 103 mm Hg, is reasonable because 7.6 is less than 8.
422
Chapter 13 • Lesson 1
What is the relationship between the temperature in kelvins and the
average kinetic energy of particles?
As a substance is heated, its particles absorb energy, some of which is stored
within the particles. This stored portion of the energy, or potential energy,
does not raise the temperature of the substance. The remaining absorbed
energy does speed up the particles—that is, increases their kinetic energy.
This increase in kinetic energy results in an increase in temperature.
READING SUPPORT
Build Vocabulary:
Word Origins Kinetic comes
from the greek word kinetos,
meaning “to move.” Kinetic
energy is the energy an
object has because of its
motion. Some sculptures are
kinetic. What characteristic
do they share?
Average Kinetic Energy The particles in any collection of atoms or molecules at a given temperature have a wide range of kinetic energies. Most of
the particles have kinetic energies somewhere in the middle of this range.
Therefore, we use average kinetic energy when discussing the kinetic energy
of a collection of particles in a substance. At any given temperature, the particles of all substances, regardless of physical state, have the same average
kinetic energy. For example, the ions in table salt, the molecules in water, and
the atoms in helium all have the same average kinetic energy at room temperature, even though the three substances are in different physical states.
Figure 13.3 shows the distribution of kinetic energies of water molecules at two different temperatures. The green curve shows the distribution
of kinetic energy among the water molecules in cold water. The purple curve
shows the distribution of kinetic energy among the water molecules in hot
water. In both cases, most of the molecules have intermediate kinetic energies, which are close to the average value. Notice that molecules at the higher
temperature have a wider range of kinetic energies.
The average kinetic energy of the particles in a substance is directly
related to the substance’s temperature. An increase in the average kinetic
energy of the particles causes the temperature of a substance to rise. As a substance cools, the particles tend to move more slowly, and their average kinetic
energy decreases.
Lower temperature
(cold water)
Percent of molecules
Higher temperature
(hot water)
Kinetic Energy and Temperature
CRITICAL THINKING Direct students to Figure 13.1.
Ask What does the intersection point of the green
and purple curves indicate? (The particles have the
same kinetic energy.)
Explore
Class Activity
PURPOSE Students will be able to visualize what is
happening in a gas as the average kinetic energy
increases.
MATERIALS cardboard containers (e.g., half-pint
milk cartons), ball bearings
PROCEDURE Give students cardboard boxes
Interpret Graphs
Distribution of Molecular Kinetic Energy
Explain
Figure 13.3 The green and
purple curves show the kinetic
energy distributions of a typical
collection of molecules at two
different temperatures.
a. Infer Which point on each
curve represents the average
kinetic energy?
containing the same number of ball bearings.
Have students shake the boxes slowly at first.
Then have them gradually increase the rate of
shaking and observe what happens. Tell students
that the shaking is analogous to adding energy
to the particles in a gas. The greater the rate of
the shaking, the more energy is added. Then ask
how an increase in energy affects the frequency
of collisions.
EXPECTED OUTCOME Student should hear and feel
the increase in number of collisions as the rate of
shaking (or the amount of energy added) increases.
b. Compare and Contrast
Compare the shapes of the curves
for cold water and hot water.
c. Predict What would happen
to the shape of the curve if the
water temperature were even
higher? Even lower?
Kinetic energy
States of Matter 423
Answers
Check for Understanding
How does kinetic theory explain gas pressure?
To assess students’ understanding of the kinetic theory, ask them to work in pairs and
to create a scenario that is analogous to the kinetic theory. Have each pair illustrate in
a diagram what happens to ‘gas particles’ in their scenario when conditions such as
pressure and temperature change.
(check students’ diagram)
ADJUST INSTRUCTION If students have difficulty creating or diagramming their
scenarios, have them create a bulleted list of facts about the kinetic theory as it
relates to gas pressure and temperature. Then provide students with additional
practice where they can reference their list to describe the behavior of gas particles
under conditions of varying pressure and temperature such as those described in
the text.
1.
2.
51.3 kPa, 0.507 atm
33.7 kPa is greater than 0.25 atm
READING SUPPORT A kinetic sculpture has moving
parts. Some are free-hanging mobiles; some are
stabiles with motors.
FIGURE 13.3
a.
b.
c.
a point near the peak of the curve
The curves have the same overall shape, but the
curve for hot water is wider with a lower peak.
At an even higher temperature, the graph
would be wider than the purple curve with a
lower peak; at an even lower temperature, the
graph would be narrower than the green curve
with a higher peak.
States of Matter
423
LESSON 13.1
Kinetic Energy and Temperature
Connect to
ASTRONOMY
Astronomers classify nebulae into two broad
categories—bright and dark. Bright nebulae are
close enough to stars that they glow. Dark nebulae
are illuminated only if something bright, like a star
cluster, is in the background. Dark nebulae are the
sites of star birth while bright nebulae are the sites
star death. But nebulae do not stay in one category
or the other forever. For example, once a star is born,
a dark nebula changes into a bright nebula. There
are several types of dark and bright nebulae. These
nebulae are named for their physical appearance
and/or chemical makeup. The boomerang nebula
shown in Figure 13.4 is a type of bright nebulae
called a planetary nebula. Planetary nebulae are
named for their round shape and resemblance to
planets. An emission nebula is another type of bright
nebula. Have interested students research why
an emission nebula is so named. Then have them
compare and contrast emission nebulae to planetary
nebulae.
Figure 13.4
The Coldest Place in the Universe
The boomerang nebula is the
coldest known region of space. A
nebula is a large cloud of gas and
dust spread out in an immense
volume. Gases are moving rapidly
away from a dying star at the
center of this nebula. The rapid
expansion of these gases is the
reason why this nebula is so cold.
Evaluate
Ask What is kinetic energy? (energy due to the
motion of an object) Ask How is the average
kinetic energy of a collection of particles related
to temperature? (Average kinetic energy is directly
proportional to the Kelvin temperature. Higher
temperatures reflect a greater average kinetic
energy.)
Then direct students to complete 13.1 Lesson Check
Reteach
Have students look at Figure 13.3 again. Point
out that the distribution of kinetic energy in cold
water is represented by the green curve. Point out
that the distribution of kinetic energy in hot water
is represented by the purple curve. Ask In which
sample is the average kinetic energy of the particles
higher? (hot water) Explain how this graph applies
to gases.
S
13.1 Lesso
LessonCheck
3.
Describe Briefly describe the assumptions of
kinetic theory as applied to gases.
4.
Explain Use kinetic theory to explain what
causes gas pressure.
5.
7. Calculate Convert the following pressures to
kilopascals.
a. 0.95 atm
b. 45 mm Hg
8. Predict A cylinder of oxygen gas is cooled
from 300 K (27°C) to 150 K (Ź123°C). By what
factor does the average kinetic energy of the
oxygen molecules in the cylinder decrease?
Explain How is the Kelvin temperature of a
substance related to the average kinetic energy of
its particles?
6. Apply Concepts Describe the behavior of an oxygen molecule in a sealed container of air. Include
what happens when the molecule collides with
another molecule or the container walls.
BIGIDEA KINETIC THEORY
9. Why does a gas take the shape and volume of
its container?
424 $IBQUFSt-FTTPO
Lesson Check Answers
3.
5.
Chapter 13 • Lesson 1
M
OBLE
4.
424
E
To assess students’ comprehension of kinetic theory
as it applies to gases, pose the following questions.
NLIN
PR
Informal Assessment
You could reasonably expect the particles of all substances to stop moving at some very low temperature. The particles would have no kinetic energy
at that temperature because they would have no motion. Absolute zero (0 K,
or Ź273.15°C) is the temperature at which the motion of particles theoretically ceases. No temperature can be lower than absolute zero. Absolute zero
has never been produced in the laboratory. However, a near-zero temperature
of about 0.000 000 000 1 K (0.1ñ10Ź9 K), which is 0.1 nanokelvin, has been
achieved. The coldest temperatures recorded outside of the laboratory are
from space. In 1995, astronomers used a radio telescope to measure the temperature of the boomerang nebula shown in Figure 13.4. At a temperature of
about 1 K, it is the coldest known region of space.
Average Kinetic Energy and Kelvin Temperature The Kelvin temperature scale reflects the relationship between temperature and average kinetic
The Kelvin temperature of a substance is directly proportional
energy.
to the average kinetic energy of the particles of the substance. For example, the particles in helium gas at 200 K have twice the average kinetic energy
as the particles in helium gas at 100 K. The effects of temperature on particle
motion in liquids and solids are more complex than in gases.
O
LESSON 13.1
Extend
A gas is composed of tiny
particles whose motion is
rapid, constant, and random.
Collisions between particles
are perfectly elastic.
Gas pressure is the result of
simultaneous collisions of billions
of rapidly moving particles with
an object.
The Kelvin temperature is
directly proportional to the
average kinetic energy of the
particles.
6.
8.
The oxygen molecule moves in
straight-line random motion until
it collides with another molecule
or with the side of the container.
After a collision, the direction of
the motion changes.
a. 96 kPa
b. 6.0 kPa
by one-half
9.
BIGIDEA As gas particles move,
7.
they spread apart filling all available
space.