92 Chapter 3

Lauric acid is a solid that is found in coconuts andprocessed foods that are made with coconut oil.Lauric acid is also used to make some soaps andcosmetics. In this lab, you will measure thetemperature of ice and of lauric acid as these solidsare heated and melt. You will graph the data youcollect and compare the heating curves for ice andlauric acid.

Problem What happens to the temperatureof a substance during a phase change?

Materials• 500-mL beaker• crushed ice• thermometer• hot plate• clock with second hand• test tube of lauric acid with thermometer• glass stirring rod• graph paper

For the probeware version of this lab, seethe Probeware Lab Manual, Lab 1.

Skills Measuring, Using Graphs

Procedure

Part A: Heating Ice1. On a sheet of paper, make a copy of the data

table shown. Start with 11 blank rows, butleave space below your data table to add morerows, if necessary.

2. Fill a 500-mL beaker halfway with crushed ice.CAUTION Use care when handling glassware toavoid breakage. Wipe up any spilled ice rightaway to avoid slips and falls.

3. Place the beaker on a hot plate. Don’t turn thehot plate on yet. Insert a thermometer into theice. Because it takes several seconds for thethermometer to adjust to the temperature ofits surroundings, wait 20 seconds and thenmeasure the temperature of the ice. Recordthis temperature next to the 0 minutes entryin your data table.

4. Turn the hot plate to a low setting. CAUTION Be careful not to touch the hot platebecause contact with the hot plate could cause a burn.

5. Observe and record the temperature at one-minute intervals until all the ice has changedto liquid water. Circle the temperature atwhich you first observe liquid water and thetemperature at which all the ice has changedto liquid water.

Data Table

01

Temperature ofWater (�C)

Time(minutes)

Temperature ofLauric Acid (�C)

Investigating Changes in Temperature During Heating of Solids

92 Chapter 3

Investigating Changes in Temperature During Heating of SolidsObjectiveAfter completing this activity, studentswill be able to• explain the constant temperature of a

substance that is undergoing a phasechange.

Students might think the temperatureshould keep increasing as the ice melts.Ask them to predict the shape of themelting curve. After performing the lab,ask students to compare theirpredictions to the actual curves.

Skills Focus Measuring, UsingTables and Graphs

Prep Time 30 minutes

Advance Prep Buy crushed ice orcrush it by placing ice cubes into aplastic bag and hitting them with amallet while wearing goggles. Pourgranular lauric acid into the test tubesand insert a thermometer into each testtube. Rather than discarding the lauricacid after the first class, leave thethermometers in the test tubes andallow the test tubes to cool to roomtemperature. The thermometers will beembedded in the solidified lauric acid.

Class Time 45 minutes

Safety Provide only nonmercurythermometers. Position hot plates awayfrom the edges of tables. Place powercords behind the hot plates, where theyare not likely to become entangled witharms or clothing. Once a hot plate isturned on, students should not touch it.

Teaching Tips • Emphasize the importance of making

an accurate measurement of the initialtemperature of the ice.

• You may wish to save time by havingsome students perform Part A of thelab and others perform Part B.Students can then exchange databefore making their graphs.

• To help students construct theirgraphs, show a sample graph on anoverhead transparency. Include thegrids for the horizontal and verticalaxes, but not the data.

• You may wish to postpone thegraphing of the results of Part A (Step 7) to the end of the lab, after all data have been collected.

L2

Probeware Lab Manual Versions of thislab for use with probeware available fromPasco, Texas Instruments, and Vernier are inthe Probeware Manual.

States of Matter 93

Analyze and Conclude1. Using Graphs Describe the shape of your

graph for ice.

2. Analyzing Data What happened to thetemperature of the ice-water mixture duringthe phase change?

3. Drawing Conclusions What happened tothe energy that was transferred from the hotplate to the ice during the phase change?

4. Comparing and Contrasting Compare the shapes of the graphs for ice and for lauricacid. Compare the melting points of ice andlauric acid.

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6. After all the ice has melted, make five moremeasurements of the temperature at one-minute intervals. Turn off the hot plate.

7. Graph your data with time on the horizontalaxis and temperature on the vertical axis.

Part B: Heating Lauric Acid8. Empty the water from the beaker into the sink.

Fill the beaker halfway with cool tap water.

9. Place a test tube containing lauric acid anda thermometer into the beaker. If necessary,add or remove water from the beaker so thatthe surface of the water is above the surfaceof the lauric acid but below the opening ofthe test tube.

10. Place the beaker on the hot plate. After 20 seconds, measure the temperature of thelauric acid. Record this temperature next tothe 0 minutes entry in your data table.

11. Repeat Steps 4 through 7 using the lauric acidinstead of the ice. To keep the temperature thesame throughout the water bath, use the glassstirring rod to stir the water after you takeeach temperature measurement.

Expected Outcome In Part A, if thereadings are taken quickly enough, thefirst few temperature readings may bebelow 0°C. The temperature readingsshould remain at 0°C until all the ice hasmelted. The temperature should begin to rise once the ice has melted. Heatingsolid lauric acid raises its temperature toits melting point of 43.2°C. The tempera-ture will begin to rise again after thelauric acid has melted.

Sample Data

Analyze and Conclude1. The graph rises quickly to 0°C andremains horizontal at that temperaturefor a number of minutes. Then, it beginsto rise again. 2. The temperature remained constantuntil the phase change was completed. 3. At first, the energy absorbed by theice was used to overcome the forces ofattraction holding water molecules infixed positions. After all of the ice hadmelted, the energy absorbed increasedthe kinetic energy of the molecules inthe liquid water.4. The two graphs had similar shapes.However, ice melted at 0�C and lauricacid melted at about 43�C.Logical

States of Matter 93

Time (min.)

Lauric acid

Water

Tem

per

atu

re (

˚C)

80

60

40

0

20

-200 5 15 252010

Typical Melting Curves

Have students pool and comparetheir data with students nationwideby visiting the Prentice Hall Website at www.PHSchool.com.

94 Chapter 3

CHAPTER

3 Study Guide3.1 Solids, Liquids, and Gases

Key Concepts

• Materials can be classified as solids, liquids, orgases based on whether their shapes and volumesare definite or variable.

• The kinetic theory of matter states that all particles of matter are in constant motion.

• There are forces of attraction among the particlesin all matter.

• The constant motion of particles in a gas allows agas to fill a container of any shape or size.

• A liquid takes the shape of its container becauseparticles in a liquid can flow to new locations. Thevolume of a liquid is constant because forces ofattraction keep the particles close together.

• Solids have a definite volume and shape becauseparticles in a solid vibrate around fixed locations.

Vocabulary

solid, p. 69; liquid, p. 69; gas, p. 70; kinetic energy, p. 71

3.2 The Gas Laws

Key Concepts

• Collisions between particles of a gas and the wallsof the container cause the pressure in a closedcontainer of gas.

• Factors that affect the pressure of an enclosed gasare its temperature, its volume, and the number ofits particles.

• Raising the temperature of a gas will increase itspressure if the volume of the gas and the numberof particles are constant.

• Reducing the volume of a gas increases its pressureif the temperature of the gas and the number ofparticles are constant.

• Increasing the number of particles will increase thepressure of a gas if the temperature and thevolume are constant.

• The combined gas law can be expressed as

�

Vocabulary

pressure, p. 75; absolute zero, p. 78; Charles’s law, p. 78; Boyle’s law, p. 79

P2V2T2

P1V1T1

3.3 Phase Changes

Key Concepts

• Melting, freezing, vaporization, condensation,sublimation, and deposition are six common phase changes.

• The temperature of a substance does not changeduring a phase change.

• Energy is either absorbed or released during aphase change.

• The arrangement of molecules in water becomesless orderly as water melts, and more orderly aswater freezes.

• Evaporation takes place at the surface of aliquid and occurs at temperatures below theboiling point.

Vocabulary

phase change, p. 84; endothermic, p. 86; heat of fusion, p. 86; exothermic, p. 86; vaporization, p. 88; heat of vaporization, p. 88;evaporation, p. 89; vapor pressure, p. 89;condensation, p. 90; sublimation, p. 91; deposition, p. 91;

Web Diagram Use information from the chapter tocomplete the web diagram on phase changes.

Thinking Visually

Phasechanges

a. ? b. ?

Deposition

Exothermic

Sublimation

Melting c. ? d. ?

94 Chapter 3

Study Guide

Study TipStudy With a PartnerOn occasion, study with a friend. Quizeach other, compare notes from classlectures, go over homework answers,and discuss concepts that you need helpwith understanding.

Thinking Visuallya. and b. Condensation, freezingc. Endothermicd. Vaporization

Assessment

If your class subscribes to iText, your students can go online to access an interactive version of theStudent Edition and a self-test.

Reviewing Content1. b 2. c 3. c4. b 5. a 6. d7. c 8. b 9. c

10. a

Chapter 3

Print• Chapter and Unit Tests, Chapter 3

Test A and Test B• Test Prep Resources, Chapter 3• Transparencies, Section 3.1

Technology• Computer Test Bank, Chapter Test 3• iText, Section 3.1• Go Online, PHSchool.com, Chapter 3

Chapter Resources

States of Matter 95

CHAPTER

3 Assessment

Choose the letter that best answers the question orcompletes the statement.

1. Which state of matter has a definite volume but avariable shape?

a. solid b. liquid c. gas d. vapor

2. In which state(s) of matter can materials take theshape of their containers?

a. solid and liquid b. solid and gasc. liquid and gas d. liquid only

3. Which statement is true about the atoms inhelium gas?

a. They travel in circular paths.b. They have strong attractions to

one another.c. They are not closely packed.d. They are arranged in an orderly pattern.

4. If the speed of an object increases, its kinetic energy

a. decreases. b. increases.c. stays the same. d. is unpredictable.

5. The SI unit of pressure is thea. pascal. b. newton.c. square meter. d. psi.

6. Increasing which variable would decrease thepressure of a contained gas?

a. temperature b. number of particles c. boiling point d. volume

7. Boyle’s law relates pressure and a. temperature. b. number of particles.c. volume. d. mass.

8. Which of the following changes is exothermic?a. evaporation b. freezingc. boiling d. sublimation

9. The phase change that is the reverse ofvaporization is

a. freezing. b. melting.c. condensation. d. evaporation.

10. Which of these phase changes does NOT involvechanging a liquid into a gas?

a. sublimation b. vaporization c. evaporation d. boiling

Reviewing Content

11. Provide an example of each of the three states ofmatter that exist at room temperature.

12. Compare and contrast liquid water and ice in termsof how definite their shapes and volumes are.

13. What three assumptions about particles in a gasare made by the kinetic theory?

14. Using the kinetic theory, explain why a liquid hasa definite volume but a gas does not.

15. How do the way that atoms are arranged inliquid mercury and solid copper affect themovement of mercury and copper atoms?

16. Using the kinetic theory, explain what causes gas pressure.

17. What three factors affect the pressure of a gas in a closed container?

18. If a piston moves downward in a cylinder, whathappens to the volume and pressure of the gas inthe cylinder? The temperature remains constant.

19. What happens to the speed of the particles insidean air-filled balloon if the temperature of theballoon increases?

20. Using the kinetic theory, explain why the pressureof a gas increases when its temperature increases.

21. How are the pressure and volume of a gas related?

22. How does an endothermic phase change differfrom an exothermic phase change?

23. Compare the vapor pressure of water at 10°Cwith its vapor pressure at 50°C.

24. Explain why water has a different boiling point at an elevation of 3000 meters than it does at sea level.

Understanding Concepts

Interactive textbook withassessment at PHSchool.com

Assessment (continued)

Understanding Concepts11. Examples might include solidcopper, liquid water, and the heliuminside a balloon as a gas.12. Both liquid water and ice have adefinite volume. Ice has a definite shape, but liquid water does not.13. The particles are in constant,random motion. The motion of oneparticle is unaffected by the motion of other particles unless the particlescollide. Under ordinary conditions,forces of attraction between particlescan be ignored. 14. The attractions between theparticles in a liquid are strong enough to keep the particles close together.Without any significant attractionsbetween particles in a gas, the particlesare free to expand into any volume thatis available. 15. The atoms in copper vibrate aroundfixed positions. The atoms in mercurycan flow past one another. 16. Gas pressure is caused by collisionsof atoms with their containers.17. Temperature, volume, and thenumber of particles 18. The volume decreases and thepressure increases.19. The particles in the air move faster,on average, when the temperatureincreases because they have morekinetic energy.20. When the temperature of a gasincreases, the particles have greaterkinetic energy, on average, and movefaster. Thus, atoms hit the walls of thecontainer more often and with greaterforce, causing the pressure to increase.21. The volume of a gas is inverselyproportional to its pressure.22. During an endothermic phasechange, energy is absorbed by thesystem. During an exothermic phasechange, energy is released by thesystem.23. The vapor pressure of water isgreater at 50°C than it is at 10°C.24. Water boils when its vapor pressurebecomes equal to atmospheric pressure.At 3000 m, the atmospheric pressure islower than it is at sea level. Thus, vaporpressure equals atmospheric pressure ata lower temperature, and water boils ata lower temperature.

States of Matter 95

Homework GuideSection

3.13.23.2

Questions1–4, 11–16, 335–7, 17–21, 27–28, 30–32, 35–368–10, 22–26, 29, 34, 37

96 Chapter 3

CHAPTER

3 Assessment (continued)

25. Classifying If you take a helium balloon frominside a warm house to outside on a snowy day,what will happen to the balloon? Could youclassify this change as a phase change? Explainyour answer.

26. Comparing and Contrasting Compare themelting and freezing of water in terms of (a) thetemperature at which these processes take placeand (b) the energy involved in these processes.

Use the graphs to answer Questions 27–29.

27. Using Graphs Which graph represents whathappens to the pressure in a tire as air is addedto the tire? Assume the temperature of the gasis constant.

28. Using Graphs Which graph represents whathappens to the pressure in an aerosol can if thecan is heated?

29. Applying Concepts Which graph representstemperature versus time during a phase change?

30. Making Generalizations The pressure of a gasis directly proportional to its temperature in kelvins.Using P1, P2, T1, and T2, write a mathematicalequation that expresses this relationship.

31. Calculating An automobile tire has a pressureof 325 kPa when the temperature is 10°C. If thetemperature of the tire rises to 50°C and itsvolume is constant, what is the new pressure?

32. Calculating A gas sample occupies 4.2 L at apressure of 101 kPa. What volume will it occupyif the pressure is increased to 235 kPa?

Math Skills

Critical Thinking

33. Using Models If there is a gas leak in thebasement of a building, you will soon notice anodor throughout the house. However, if there is awater leak in the basement, you will need to goto the basement to detect the leak. Use thekinetic theory to explain the differences.

34. Inferring A student examines a thermometerplaced in a can containing a substance that isbeing heated. The temperature remains the samefor several minutes, and then it starts to rise.Without looking in the can, how does the studentknow what is occurring in the can?

35. Relating Cause and Effect In Earth’satmosphere, pressure and temperature bothdecrease as altitude increases. Weather balloonsexpand as they rise. Which has more effect on theweather balloon, the decrease in pressure or thedecrease in temperature? Explain your answer.

36. Drawing Conclusions In a car engine, air andgasoline vapors are mixed in a cylinder. A pistonis pushed into the cylinder before a spark ignitesthe mixture of gases. When the piston is pushedinto the cylinder, what happens to the pressureof the gases in the cylinder?

37. Writing in Science Unpopped popcorn kernelscontain a small amount of water. Use what youknow about vaporization and how gases behaveto explain why popcorn pops when it is heated.

Making a Poster The gas laws have many practicalapplications in cooking. Make a poster, includingdiagrams, that shows how two factors that affect gasesaffect cooking. Examples might include explainingwhy cakes rise while baking or why some recipesspecify high-altitude temperatures and cooking times.

Performance-Based Assessment

Concepts in Action

A. C. B.

For: Self-grading assessment

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Web Code: cca-1030

A B C

96 Chapter 3

Critical Thinking25. A balloon that is flexible will shrink.This observed change is not a phasechange because helium is a gas beforeand after the change.26. (a) Water melts and freezes at thesame temperature. (b) Melting is anendothermic process. Freezing is anexothermic process.27. Graph A 28. Graph A29. Graph C

Math Skills30. P1/P2 � T1/T2 or P1/T1 � P2/T231. 371 kPa 32. 1.8 L

Concepts in Action33. There is almost no attractionbetween particles in a gas. They willquickly spread throughout the building.Because particles in a liquid stronglyattract one another, they remain closetogether and don’t spread throughoutthe building (unless the water quantityis large and there is no drain).34. Because energy is being added butno increase in temperature occurs, aphase change is occurring in the can. 35. A decrease in pressure causes anincrease in volume. A decrease intemperature causes a decrease involume. Because the volume of theballoon increases, the decrease inpressure must affect the balloon morethan the decrease in temperature.36. The pressure increases. 37. Heating causes the water to vaporize.With continued heating, the pressure ofthe vapor increases because the volumeof the confined vapor is constant. Eventu-ally, the increased pressure causes thekernel to burst open.

Chapter 3

Performance-Based AssessmentPossible poster topics: Gas bubbles formed incake batter increase in volume when the batter isheated, causing the cake to rise. Cake mixes oftenhave instructions for baking at higher altitudesbecause the boiling point of water decreases athigher elevations. In a pressure cooker, the volumeof air is constant. Heating the air increases both itstemperature and pressure, and the food cooks in ashorter amount of time.

Your students can independentlytest their knowledge of the chapterand print out their test results foryour files.

States of Matter 97

Standardized Test Prep

Choose the letter that best answers the question orcompletes the statement.

1. A material can be classified as a liquid if(A) it has a definite shape and a

definite volume.(B) it has a definite shape and a

variable volume.(C) it has a variable shape and a

definite volume.(D) it has a variable shape and a

variable volume.(E) its particles vibrate around fixed locations.

2. Which statement best explains what must takeplace for water to boil?(A) The water releases energy to its

surroundings.(B) Bubbles rise to the surface of the water.(C) The vapor pressure of the water becomes

equal to atmospheric pressure.(D) Molecules at the surface of the water

overcome the attractions of neighboringmolecules.

(E) The temperature of the water increases.

3. Condensation is the phase change in which asubstance changes from(A) a solid to a gas.(B) a solid to a liquid.(C) a liquid to a solid.(D) a liquid to a gas.(E) a gas to a liquid.

4. Which of these statements about an enclosedgas is true? (Assume all quantities are constantexcept the two variables described in eachstatement.)(A) Raising the temperature of a gas will

increase its pressure.(B) Increasing the volume of a gas will increase

its pressure.(C) Reducing the number of particles of a gas

will increase its pressure.(D) The volume of a gas is inversely

proportional to its temperature in kelvins.(E) The volume of a gas is directly proportional

to its pressure.

Use the illustration to answer Question 5. Assume thatthe number of particles of gas in container A equals thenumber of particles of gas in container B.

5. If the temperature is constant, the pressure incontainer B is(A) one half the pressure in container A.(B) twice the pressure in container A.(C) equal to the pressure in container A. (D) five times the pressure in container A.(E) one fifth the pressure in container A.

6. During an endothermic phase change,(A) the temperature of a substance rises.(B) the temperature of a substance decreases.(C) energy is transferred from a substance to

its surroundings.(D) a substance absorbs energy from

its surroundings.(E) there is no transfer of energy.

Test-Taking Tip

Watch For QualifiersThe words best and least are examples of quali-fiers. If a question contains a qualifier, more thanone answer will contain correct information.However, only one answer will be complete andcorrect for the question asked. Look at the ques-tion below. Eliminate any answers that are clearlyincorrect. Then choose the remaining answer thatoffers the best explanation for the question asked.

Choose the best explanation for why oneparticle in a gas does not affect other particlesin a gas unless the particles collide.(A) Particles in a gas are constantly moving.(B) All the particles in a gas have the same

kinetic energy.(C) There are no forces of attraction among

particles in a gas. (D) There are billions of particles in a small

sample of a gas.(E) Particles in a gas are relatively far apart.

(Answer: E)

1.0 L

0.5 L

A B

Standardized Test Prep1. C 2. C 3. E4. A 5. B 6. D

States of Matter 97