‘~ SaeThUCe Co~tte~n

~Students know the states of matter(solid, liquid, gas) depend on molecularmotion.~ Students know that in solids the atomsare closely locked in position and can onlyvibrate; in liquids the atoms and moleculesare more loosely connected and can collidewith and move past one another; and ingases the atoms and molecules are free tomove independently, colliding frequently.

What You’ll LearnD~ Recognize that matter is

made of particles thatalways are moving.

~ Compare the motion ofparticles in solids, liquids,and gases.

~ Compare the arrangementof particles in solids, liquids,and gases.

*hy It’s ImportantAll matter that surroundsyou is composed of particlesthat are in constant motion.

Vocabdaryrandom motionsolidliquidgas

Review Vocabdarymatter: anything thattakes up space and has mass(Chapter 4)

254 Chapter 6 a States of Matter

Rea8-World Reading Connection A glass of ice-cold lemohiade may be just the thing to cool you off after a hard game of~jsocceL This drink also contains two states of matter. Lemonad~is a liquid that easily flows flom a glass when you tip it Solid ickeeps its shape until it melts. The air in a soccer ball is a thirdstate of matter Air is a gas that expands to fill the ball

What are states of matter?The ice, soft drink, and bubbles in Figure 1 are examples of

the three familiar states of matter solids, liquids, and gases Theice is a solid, the soft drink is a liquid, and the bubbles are filledwith a gas. These are the three states of matter that usuallyoccur on Earth.

Stars, such as the Sun, are made of another state of mattercalled plasma. The plasma state is similar to the gas state andusually occurs at high temperatures. A plasma is made of atomsthat have been brolcen apart and contains electrically chargedparticles. Although plasmas can be found in lightning and influorescent lights, the plasma state is not common on Earth.

Solids, Liquids, and Gases~ The state of matter depends on the motion of~its particles.

Figure 1 The ice, soft drink,and bubbles are examples ofthree states of matter.

‘DCt

~ce is a solid.

‘Dr‘~

The bubblescontain a gas.

PartkDes ~n MatterRecall from Chapter 4 that all matter is made of very small par

ticles called atoms. In Chapter 5 you read that atoms can combineto form molecules, which are also very small particles of matterAll objects, such as the flower shown in Figure 2, are made ofthese particles

In all objects and materials, these tiny particles of matter arealways in motion Even though the flower in Figure 2 is not moving, the atoms and molecules in the flower are always movingome particles move to the left or the right, some move up andlown, and some move in other directions

Particles in matter move in a type of motion called randomlotion In random motion, particles can move in any direction

can have different speeds In any object, the number of partis moving in one direction is always equal to the number of par

<les moving in the opposite direction As particles move, they~ collide with other particles These collisions can change a pare’s direction of motion and its speed

In random motion, how are particles moving?

rDes Attractrthey are moving, atoms and molecules usually exert a pull,

attractive force, on each other These forces tend to pull par-Closer together Recall from Chapter 4 that atoms contain

~veIy charged protons and negatively charged electrons. These~c charges can cause attractions between the atoms and mole

~: matter. If particles move closer together, the attractive‘Setween them become stronger. As they move farther apart,action between them becomes weaker.

Figure 2 The particles in all matter aremoving in random motion. They move indifferent directions and at different speeds.Explain why an object does not move when itsparticles are in random motion.

ObservingFluid Motion

ProcedureI. Fill a clear

glass or jarwith lukewarm tap water.

2. Allow the container tosit undisturbed for 10minutes.

3. Add three drops offood coloring to thewater. Be careful todisturb the water aslittle as possible.

Analysis1. Describe what

occurred when thefood coloring wasadded to the water.

2. Explain why thisoccurred.

3. Evaluate Would thefood coloring mixfaster if the water wasa warmer temperature?Explain.

Lesson 1 • Solids, Liquids, and Gases 255

I‘~1

SolidsWhy is the dumbbell in FAgure 3 a solid? If you hold the

dumbbell in your hand, it doesn’t flow or make a puddle like waterdoes. If you place the dumbbell in a box, its shape doesn’t changeto match the shape of the box. Like all solids, the volume andshape of a dumbell do not change. A solid is matter with a fixedshape and a fixed volume.

SOENCE USE V. COMMON USEstateScience Use a condition ofmatter. Three common states of:matter are solid, liquid, and gas.Common Use a condition ofmind or being. Before the bigtest, the students were in anervous state.

The Forces Between ParticVes in a SoNdThe motion of the particles and the strength of the attractive

forces between them determine whether a substance is a solid, aliquid, or a gas. As in all matter, the particles in a solid always arein motiont However, the particles in a solid are so close togetherthat the attractive forces between them are strong.

In a solid, why are the attractive forces between‘~4~4 particles strong?

The Motion of Partides in a SoDidThe particles in a solid are attracted to each other by strong

forces that keep the particles close together. B~cause the forcesbetween particles are strong, particles in a solid cannot move veryfar from each other. The motion of the particles in a solid is shownin F~g~we 3. Each particle moves only a short distance back andforth between neighboring particles. As a result, the particles in asolid stay in nearly the same position, vibrating back and forth inall directions. Because the particles in a solid don’t move from oneplace to another, the shape and volume of the solid remain fixed.

Figure 3 The particles thatmake up a solid vibrate in fixedlocations. A solid has a fixedshape and a fixed volume.

116 Chapter 6 States of Matter

.~jre 4 The containerscontain the same volume ofiquid The shapes of liquid inhe two containers are differnt because the containers

jave different shapes.

iquidsUnlike a solid, a liquid can flow and does not have a fixed

iape As shown in Fug~we 4, a liquid has the shape of the conuner in which it is placed A liquid is matter with a fixed volumet not a fixed shape.

£

,~.i Forces Between Partides in a LiquidThe attractive forces between particles in a liquid are weakerin they are in a solid These forces are not strong enough toep the particles in fixed positions As a result, the particles in a

quid move more freely than they do in a solid

ot~on of Part~des rn a LiqwdF~g~re 5 shows how the particles in a liquid move In a solid, a

article stayrin one place and moves a short distance back and~th In a liquid, particles can move past neighboring particles

Because the particles in a liquid can move from one place toother, a liquid can flow and change shape However, the forces

i:etween particles in a liquid are strong enough to keep the partiJes close to each other. This causes the volume of the liquid toemain fixed

Figure 5 Particles in aliquid are close together, butcan slide past each other.Compare the motion of particlesin a solid and in a liquid.

257

Every second you are surrounded by a gas—the air around yoü~When you breathe, you force this gas to flow into and out of yourlungs. Even though a gas can flow, it is different from a liquid. A Igas is matter that has no fixed volume and no fixed shape.

Changes in Shape and VollumeGases and liquids do not have a fixed shape. Unlike solids or

liquids, a gas also does not have a fixed volume If any amount ofgas is put in a container, the gas expands until it fills the containéiias shown in Figw’e 6. This means that the shape and the volume 1,of the gas depend on the shape and volume of the container thegas is in.

Forces Between Partvdlles in a GasThe panticles in a gas are much farther apart than the particles

in a solid or a liquid, as shown in Figure 1 Because the particles in’a gas are so far apart, the forces between these particles are weakAs a result, the particles in a gas are not held together and move I.freely past each other.

Figure 6 A gas spreads outuntil it has the same volumeas its container.Describe how the volume of thegas changes.

WORD OmGlNgasfrom Greek khaos; meansempty space

Gases

Figure 7 Particles ina gas are far apart andmove freely.

25S chapter 6 States of Matter

otaon of Partacles an a Gas‘,side a container, gas particles move in random motion fromice to place As gas particles move, they collide with each otherI with the sides of the container Between collisions, a gas partimoves in a straight line. However, a collision can make the par

move in a different direction and can also change its speed.cause the particles in a gas can move freely from place to place,as does not have a fixed shape

~\ What can cause the direction and speed of a particlein a gas to change?

Unlike particles in solids and liquids, gas particles are not held~gether by attractive forces. As a result, gas particles spread out~til they are evenly distributed throughout a container No mati~ how large the container, the volume of a gas is always the samethe volume of the container the gas is in Table 1 summarizes

~me of the differences between solids, liquids, and gases

ceincepts t~i~~jjj~4 Interactive Table Organize information about

solids, liquids, and gases at ca8.msscience.com.

Lt.

iolidfixed shapefixed volumeparticles are close togetherstrong attractive forces between particles

rticles vibrate in all directions

,e, a liquid takes the shape of container-- ume

close together- rces between particles are weaker in liquids than

ire free to move past neighboring particles

• ‘•‘‘ v

es

Lesson 1 • Solids, Liquids, and Gases 259

ACADEMIC VOCABULARYdistribute (dih STRIHbyewt)(verb) to spread out to coversomethingSandra distributed the seedsthroughout the garden.

SummarbeCreate your own lesson summary as you write a script fora television news report.

1. Review the text after thered main headings andwrite one sentence abouteach. These are the headlines of your broadcast.

2. Review the text and write2—3 sentences about eachblue subheading. Thesesentences should tell who,what, when, where, andwhy information abouteach red heading.

3. Include descriptive detailsin your report, such asnames of reporters andlocal places and events.

4. Present your news reportto other classmates aloneor with a team.

260 Chapter 6 States of Matter

1. Write the definitions of solid,liquid, and gas in your ownwords.

2. In __________. particles canmove in any direction.

Understanding Main Ideas

3. Which state of’matter is foundin fluorescent lights and lightning strikes, but is relativelyuncommon on Earth?

A. gasB. liquidC. plasmaD. solid

Summarize the motion ofparticles in solids, liquids,and gases. C

5. Compare Copy and fill in th&graphic organizer below andcompare the distancebetween particles in solids,liquids, and gases.

SolidsLiquids~s

~

6. Compare the attractive forces jbetween particles in a solidand in a gas.

What have you learned?All matter is made of particles, such as atoms or molecules, thai

are in random motion. In solids, the particles are close togetherand they can only vibrate in place. The attractive force betweenthe particles in a solid is strong. Because of these strong forces, tli~shape and volume of a solid remain fixed.

The attraction between the particles in liquids is weaker thanthe attraction between the particles in solids. Because of theweaker attractive forces between particles, particles in liquids canmove past each other. As a result, liquids are able to flow and totake the shape of their container.

In gases, the particles are very far apart and the attractive forcSbetween them are weak. The particles of a gas move freely and cotlide with the walls of its container and other gas particles. Becausethe particles move freely, gases have no fixed shape or volume.

Using VocabuVaryStandards Check

Applying Science

4.

7. Determine how the volume of~air in a room would change ifthe volume of the room weredoubled. —

r

Sc~enc~nUneFor more practice, visit StandardsCheck at ca8.msscience.com.

Matter Changing State ca&msscience.com j~!j

N~i~ You’ll LearnCompare melting andfreezing.

Compare vaporization andcondensation.

?JCij7 It’s ImportantThe energy released whenwater changes from a gas toa liquid helps produce

D rm S.

Iocab~dary~mperaturehermal energynetting point

~ezing pointvaporizationboilingboiling pointevaporationcondensationsublimationdeposition

Rev~ w Vocab~darypotential energy: theenergy an object has due toits position (Grade 6)

Changes in States of Matter4’1M1?IF!~ Changes in energy can cause matter to changefrom one state to another.

Real~WorM Reading Corniectñon Changes in the weathercan cause changes in states of matter. In early spring, snow meltsinto liquid water. A summer rain leaves puddles of water onthe sidewalk, but the warm Sun makes the puddles evaporateinto a gas.

Temperature, Thermal Energy,and Heat

Ice and liquid water are different states of the same substance.They both are made from particles that are water molecules. Buthow can an ice cube change into liquid water? A change fromone state of matter to another is a result of two things. One ischanges in the motion of the particles. The other is the strengthof the forces aMong particles.

Moving Partides and Kinetic EnergyRecall that moving objects, such as a car or a train, have

kinetic energy. The kinetic energy of an object increases as it~speed increases. Even when an object is not moving, the particles in the object are in random motion. As a result, these particles also have kinetic energy. For example, the particles in theballoon shown in Figure 8 have kinetic energy even though theballoon is not moving.

Scâence Conde~tI Sta~dawds

~z!ents know the states of matterd, gas) depend on molecular

judents know that in solids the atomssely locked in position and can only

~ in liquids the atoms and moleculesore loosely connected and can collidend move past one another; and in

~the atoms and molecules are free to~ndependently, colliding frequently.

covers: 9.e, 9.g

Figure 8 The’gas particles inside the balloon haveenergy because they are moving.

Lesson 2 • Changes in States of Matter 261

Temperature and AverageKinetic Energy

The air inside the hot-air balloon in Figure 9?has a higher temperature than the air outside.Temperature is a measure of the average lcinetkenergy of the particles in a material. This meant:that the average kinetic energy of particles insidethe balloon is greater than the average kineticenergy of particles outside. As a result, particlesinside the balloon are moving faster on averagethan particles outside the balloon Particles inmatter move faster as the temperature increases

Measurvng TemperatureOne way to measure temperature is to use a

liquid thermometer Some thermometers have ared liquid inside a glass tube When the liquidgets warmer, the particles in the liquid begin tomove faster The particles then get farther apartand take up more space This causes the liquid toexpand and the liquid rises in the tube

The marks on a thermometer tell you the tem4:perature in degrees. Figure 10 shows three corn-:mon temperature scales. The range between thetemperatures at which water freezes and boilson the different scales is shown This range isdivided into 180 degrees on the Fahrenheit scaleIt is divided into 100 degrees on the Celsius andKelvin scales. The Fahrenheit scale is widely used~in the United States, but the Celsius scale is usually used in other countries., The Celsius and Kel?.yin scales are used in science

Figure 9 The temperature of asubstance increases as the particles movefaster and have more kinetic energy.Compare the motion of air particles inside an”doutside the balloon. [

Figure 10 The boiling and freezingpoints of water are different on the Fahrenheit, Celsius, and Kelvin temperature scales.

Common Temperature Scales

F’

Temperatureat which

water boils

L212°F

32°F

100°C 373 K

~°~- ~Temperatureat which

water freezes

Fahrenheit Celsius Kelvin

262 Chapter 6 a States of Matter

Partic~es of Matter and Potential EnergyIn addition to having kinetic energy, the particles in a substance

~~iave potential energy as a result of the forces that they exert oneach other Potential energy decreases as particles get closerkogether and increases as particles get farther apart. A ball heldabove the ground has potential energy, as shown in Figure 11. Theimount of potential energy depends on the distance between thenll and Earth If you let the ball go, its ‘p6tential energy decreases~s it gets closer to the ground. In the same way, the potential‘nergy of particles in matter decreases when the particles arecloser together

Thermal EnergyA substance also has thermal energy. Thermal energy includes

both the kinetic energy and potential energy of the particle~Dififerent states of matter have different amounts of thermal energy.Compared to the solid state, the particles of a substance in the gasstate move faster and are farther apart These particles have morekinetic and potential energy than the particles in the solid state.This means that the thermal energy of the substance in the gasstate is greater than the thermal energy in the solid state. For anygiven substance, the particles have the most thermal energy in thegas state and the least thermal energy in the solid state.

aV

The ball has more potential energy. The ball has less potential energy. I

Particles of matter have more potential energy. Particles of matter have less potential energy.

Higher Potential Energy Lower Potential Energy

Figure 11 Thepotential energy ofthe ball depends onthe distance betweenthe ball and Earth. Thepotential energy ofparticles in matterdepends on the distance between them.

What can cause the potential energy of particles inmatter to increase?

Lesson 2 o Changes in States of Matter 163

Figure 12 Adding thermalenergy to a substance can causeeither an increase in temperatureor a change of state.

.

ACADEMIC VOCABULARYremove (ree MOOV)(verb) to get rid ofMaria removed the seeds fromthe orange before she ate it.

Figure 13 Steel mustbe heated to about1,400°C before itwill melt.

Adding and Removing Thermah EnergyThermal energy can be added to a material or removed from a

material. When you heat a pot of water on a stove, thermal energy~is added to the water thermal energy flows into a material whenit is heated. When a warm bottle of water cools in a refrigerator,thermal energy is removed from the water. Thermal energy flows~out of a material when it is cooled.

How is t4ermal energy added to a material?

Thermab Energy and Changes in StateWhen thermal energy is added to a material, the thermal energ~

of the material increases Figure 12 shows that adding thermalenergy can cause the potential energy and the kinetic energy of th~particles in a material to increase If the kinetic energy increases,then the temperature of the material increases However, whenonly the potential energy increases, the temperature of the material doesn’t change. Instead, the material changes from one state ofmatter to another. To change a material from one state of matterto another, thermal energy must flow into or out of the material

Changes Between the Solid andLiquid States

The particles that make up the liquid steel and the solid steel inF~gure 13 are exactly the same. The difference between the liquid 1and the solid depends on the movement of the particles and thethermal energy they contain. Particles in the liquid steel move Ifaster and have more thermal energy. Particles in the solid steel Imove more slowly and have less thermal energy. Thermal energymust be added to a material or taken away to change it from onestate of matter to another.

164 Chapter 6 States of Matter

~e1ting occurs when a solid changes into a liquid. When youci a solid, thermal energy flows into the solid Then the tern:ture of the solid increases until the temperature reaches theIting point. The melting point of a material is the temperature~vhich the material changes from a solid to a liquid

a 14 shows how the temperature of a solid material changesit is heated and thermal energy is added At first, the temperaie of the solid increases But when the temperature reaches theJung point, the temperature of the material stops increasing Ase material changes from a solid to a liquid, the temperature stays

~nt at the melting point.

Figure 14 Why is the line on the graph horizàntalwhen melting is occurring?

,ergy Changes During MeDtingThermal energy still is being added to the material as it melts.

‘ecause the temperature is not changing, the average kifietic~ergy of the particles doesn’t change. Instead, the added thermalnergy causes only the potential energy of the particles to increase.

When the potential energy of the particles increases, therrangement of the particles in the material changes. In mostnaterials, particles move farther apart. The new arrangementauses the attractive forces between particles to ?ecome weaker.Then melting occurs, these forces have become weak enough that11e particles can move past each other. After the solid has changedcompletely into a liquid, adding thermal energy causes the temperture of the liquid to increase, as shown in Figure 14.

4-

1!0J0.

= =

the ~ernperatdre dithe liquid increases.’~...

. - - --~ -Melting — — The temperature doesn’tbegins. — change as melting occurs. -

~ — —

I—~

——

J MeltingJ ends.L The temperature of~ the solid increases.

= n = =

Figure 14 The thermal energyof the liquid is greater than thethermal energy of the solid.Energy must be added to thesolid to change it to a liquid.

Amount of thermal energy added

-J

Lesson 2 • Changes in States of Matter 265

Thermal energyadded

Thermal energyremoved

Figure 15 Melting and freezing arereversible processes. A solid gains thermal energy when it melts. A liquidloses thermal energy when it freezes.

FreezingFreezing occurs when a liquid changes into a solid. When a

material cools, thermal energy flows out of the material. Thetemperature of the material decreases until the freezing point isreached. The freezing point is the temperature at which the liquidchanges to a solid. As thermal energy continues to flow out of thematerial, the temperature remains constant at the freezing point.After all the liquid has changed to a solid, the temperaturedecreases once again as thermal energy is removed.

How does the thermal energy of a material change as~it freezes?

Freezing—The Opposite of MeltingAs Figinre U shows, freezing is the opposite of melting. For any

material, the freezing point is the same as the melting point. Whilefreezing is occurring, thermal energy is being removed from thematerial. The temperature remains constant, so the average kineticenergy of the particles doesn’t change. Instead, the potentialenergy of the particles decreases. In most materials this meansthat the particles move closer together. Then the forces betweenthe particles become strong enough for the particles to be held infixed positions. The liquid becomes a solid.

Changes Between Liquids and GasesIf you heat a pot of water on the stove, as in F~ginre 16, you will

notice bubbles forming in the water. Tiny water droplets in theform of steam rise into the air. Water in its invisible gas form,called water vapor, also rises from the pot. The liquid is changingto a gas.

266 Chapter 6 o States of Matter

Figure 16 Vaporization occurs both belowthe surface and at the surface of a liquid duringboiling.identify the substance contained in the bubbles whenwater boils

Vaporization and BodingWhen liquid water is heated, its temperature rises until it

reaches 100°C. At this temperature, liquid water changes intowater vapor The change from a liquid to a gas is calledaporization When vaporization occurs, the attractive forces

between particles are too weak to keep particles close to eachbther. Particles spread out and move independently.

Vaporization can occur within a liquid and at the surface of aliquid, as shown in Figure 16. Vaporization that occurs within a[iquid is called boiling. When a liquid boils, bubbles form withinIhe liquid. These bubbles contain particles of the material in the:gas state.

The boiling point is the temperature at which boiling occurs ina liquid. As Figae 17 shows, the temperature doesn’t change whilea liquid is boiling. Boiling ends after the liquid has changed to agas. If thermal energy continues to be added, then the temperature

~of the gas will continue to rise.

T[ktemperature ofth~ liquid increases.

Figure 17 Th&thermalenergy of a gas is greaterthan the thermal energyof a liquid. Energy mustbe added to change aliquid to a gas.

I

— L.

WORD OrnGaivaporizationfrom Latin vaporetn; meansexhalation, steam, heat

Boilingbegins.

IC’0.E

/i—-The t~mtierature doesn’tchanne as boiling occurs.

thetemperattire dfthe gas increases;

74~)

r ZZEETEZ I I,

Boilingends.

Amount of thermal energy added

Lesson 2 • Changes in States of Matter 267

268 Chapter 6 • States of Matter

Figure 18 Evaporation occurs onlyat the surface of a liquid.Compare the energy of the particles thatleave the surface with those in the liquid.

TjjjjJL4JDJ~~ Sensing -

Evaporation

Procedure

1. Complete a lab safetyform.

2. Obtain a bottle ofrubbing alcohol fromyour teacher.

3. Dip a cotton swab intothe bottle and closethe bottle.

4. Rub the alcohol-dippedswab on the back ofyour hand.

Analysis1. Describe how the

alcohol feels on yourskin.

2. Explain why alcoholfeels this way on yourskin.

EvaporationVaporization that occurs at the surface of a liquid is called

evaporation Evaporation occurs during boiling and at temperatures below the boiling point. Recall that particles in a materialmove at different speeds. Some particles at the liquid’s surface aremoving much faster than other particles. Some of these particlesare moving so fast that the attractive forces aren’t strong enoughkeep them at the surface of the liquid. As shown in Figure 18,these fast-moving particles escape into the space above the liquid.Above the liquid, the particles are far apart and the attractiveforces between them are weak. These particles move independentlyand are in the gas state.

During evaporation, the fastest particles leave the surface of theliquid. The particles that remain have less kinetic energy. Thismeans that the average kinetic energy of the liquid decreases As aresult, the liquid cools as evaporation occurs You experience thiscooling effect when perspiration evaporates from your skin

Why does a liquid cool when evaporation occurs?

Pressure and the Boiling PointThe boiling point of a liquid depends on the types of atoms and

molecules that make up the liquid The boiling point also dependson the pressure exerted on the liquid Recall the air around youexerts pressure This pressure is exerted on a pot of water heatingon a stove For the water to boil, bubbles containing water vapormust form in water. The pressure exerted on the water by theair makes it harder for these bubbles to form. As air pressureincreases, the water must be heated to a higher temperature beforebubbles of water vapor form. This means that the boiling point ofa liquid increases as the pressure on the liquid increases. As thepressure on the liquid decreases, the boiling point decreases.

/7

~ndensatDOflDn a hot day, you might see drops of water on the outside~ glass of ice-cold water. These drops of water come fromair surrounding the glass The air contains wateror—a gas The cold glass cools the air next to it Whenwater vapor in the air next to the glass becomes coolugh, it changes from a gas to a liquid The change from ato a liquid is called condensation. Early in the morning,

i might have noticed dew on the grass, as in Fug~nwe 19ing the night, blades of grass cool more quickly than theWhen their temperature becomes low enough,

idensation occurs and water droplets form

~ndensaton—The Reverse of VaporDzatrnnjure 20 shows how condensation and vaporization are

~~.ssible processes For condensation to occur, thermalergy must be removed from a gas. This causes the gas parles to move more slowly and the temperature of the gas to~rease. The gas continues to cool as thermal energy con

iues to be removed Finally its temperature becomes lowough for condensation to occur Then particles move

owly enough so that the attractive forces are able to keepparticles close together As a result, a liquid forms

Figure 20 Vaporization and condensation are reversible processes.7Thermal energy must be added to a liquid to vaporize the liquid.

Thermal energy must be removed from a gas to make it condense

Thermal energyadded

aa

Thermal energyremoved

Figure 19 Water dropletsthat form on blades of grassovernight are due tocondensation.

Lesson 2 a Changes in States of Matter 269

n©~

0

n

.4.0-I

0’S

In~1-0Jrf(0I~1

0-4,

03

0

Temperature (°C)

C

-4

ID-I

9IDzIta

‘C

C.C.IDC.

In<

m _

S

I

C

Q.

N

—~

/

I ,Or~

~banging the States of WaterJmagine that you heat a container in which there is a piece ofe ngrn’e 21 shows how the temperature of the ice changes asiermal energy is added to it

rddvng Therma~ EnergyAs the containei is heated, the temperature of the ice increases

he temperature of the ice continues to rise until the meltingjint of ice is reached Fugiwe 21 shows that the temperature stays,nstant as the ice begins to melt and change from a solid to a hq

~d Even though the temperature isn’t changing, thermal energyiist be added to the ice to change all the solid ice to liquid water.

As ice melts, how does its temperature change?

After all the ice has melted, the temperature of the water beginsincrease as the container is heated. When the water temperature

sches the boiling point of water, the temperature sto11s increasig, as shown in FBgure 21 As the container continues to beeated, liquid water changes to water vapor Finally, all the liquid~ter changes to water vapor. Adding more thermal energy thenauses the temperature of the water vapor to increase

~èmoving Thermall EnergyIce can be melted to form water by heating the ice The water

hat is formed can be changed back into ice by removing thermalnergy and cooling the water This means that the changes~etween states of matter are reversible. Figwe 22 shows how water~apor can be changed back into ice by cooling.

Figure 22 As thermalenergy is removediwatervapor changes to liquidwater, which then changesto solid ice.Infer from the graph whichchange of state requires thelargest change in thermalenergy.

Gas

100Condensation

E4’

0.2

-_A_The temperature staysconstant at the boiling pointas the gas changes to a liquid. Liquid -

FreezingThe temperature staysconstant at the freezing pointas the liquid changes to a solid.

0

Solid

Thermal energy removed

Lesson 2 • Changes in States of Matter 271

Changes Between Solids and GasesThe dry ice in Figure 23 produces a thick fog. Dry ice is solid

carbon dioxide. At room temperature, dry ice absorbs thermalenergy and changes directly into a colorless gas. Sublimation isthe change of a solid to a gas without going through the liquidstate. The thick fog around the dry ice is caused by the cold carboddioxide gas that causes water vapor in the air to condense intosmall droplets. For sublimation to occur, thermal energy must beadded to a solid. I

The opposite of sublimation is deposition, the change of a gasto a solid without going through the liquid state. The frost that jforms on the leaf shown in Figure 13 is caused by deposition. Fordeposition to occur, thermal energy must be removed from a gas.:When the leaf becomes cold enough, water vapor in the airsurrounding the leaf loses enough thermal energy to change intoa solid.

Figure 23 Sublimation causes the dryice to change to a gas.Deposition causesfrost to form on theleaf.

Changes in Energy Among Statesof Matter

The state of matter of a substance depends on the amount ofthermal energy a substance contains. For a material to changefrom one state of matter to another, thermal energy must be adde<to the material or removed. Figure 24 shows the energy changesthat occur when a material changes from one state to anotheic ~:

GAS F:~. .

Figure 24 For a change in stateoccur, thermal energy must moveinto or out of the material.List the changes in state that can occurwhen thermal energy is added to a material.

SOLID

Remove thermal energy

LIQUID

rAdd thermal energy

The temperature of a material depends on the average kineticaergy of the particles in a material. The faster these particles~ove, the higher the temperature. Thermal energy is added to a

~:aterial when it is heated. Thermal energy is removed when a~aterial cools. When a material changes from one state of matter

~ another, thermal energy must be added or removed.Melting occurs when a material changes from a solid to a liquid

~reezing is the reverse of melting. Vaporization occurs when ai,aterial changes from a liquid to a gas. Vaporization can occurfiside a liquid by boiling or at the surface by evaporation. Condenation is the reverse of vaporization. As a material changes from

~ne state to another, its temperature doesn’t change.

Summarbe~ your own lesson‘mary as you organize~utIine.

;;~ the lesson. Find andst the first red main

‘eading.

R._view the text after~he heading and list 2—3Jetails about the heading.

.~.j and list each blue~bheading that followshe red main heading.

.1st 2—3 details, key terms,nd definitions under

~ach blue subheading.

~eview additional rediain headings and their

supporting blue subheadings. List 2—3 details about‘ach.

2. Use each term in a separatesentence: evaporation, condensation, sublimation, anddeposition.

Understanding Main Ideas

3. During which change of statedo the particles in a materialbecome farther apart? ~

4. Compare temperature, thermal energy, and heat ~

5. Explain how changes in thermal energy and changes instate of matter are related.

7. Summarize Copy and fill inthe graphic organizer below toidentify the changes in statesof matter that can occur whenthermal energy is removedfrom a material, a

8. Explain why a bathroom mirror becomes fogged when youtake a shower.

9. Describe how the potentialenergy of water moleculeschanges as water changesfrom a solid to a liquid andthen from a liquid to a gas.

~1hat have you learned?

~MJL

Using Vocabulary

Standards CheckApplying Science

1. Write the definitions of freezing point and boiling point inyour own words. a

~Remove(Thermal Energy

A. vaporizationB. freezingC. deposition0. condensation

6. Compare and contrast sublimation and deposition. a Sc~enc4~i~e

For more practice, visit StandardsCheck at ca8.msscience.com.

States of Matter ca8.msscience.com Lesson 2 • Changes in States of Matter 273

How are boiling point andatmospheric pressure related?

The temperature at which water boils depends on the pressure~bove the liquid. When the liquid is in an open container, thepressure above the liquid is atmospheric pressure.

98.7

100.0

101.3

102.7

105.3

106.7

99.2

99.6

100.0

100.4

101.1

101.4

DataGraph the data in the table. Plot pressure on the’x-axis and theboiling point on the y-axis. Label each axis, including the properunits. Choose an appropriate scale for each axis.

Data Analysk1. Determine if atmospheric pressure and boiling point have a

linear or nonlinear relationship at this pressure range.

2. Determine the boiling point of water at 102 kPa.

3. Estimate the boiling point of water at 108 kPa.

a 3den~e Crn~te~it~ Students know the states of matter (solid, liquid, gas) depend on molecular motion.~ Distinguish between linear and nonlinear relationships on a graph of data.

Atmospheric Pressure andBoiling Point of Water

Pressure(kPa)

Boiling Point(°C)