Section 16.1 16.1 Thermal Energy And Matter

Section 16.1 (continued)Thermal Contraction and ExpansionThermal Contractionand ExpansionCooling AirProcedureCooling AirL2ObjectiveAfter completing this activity, studentswill be able to describe the effect of temperature onthe volume of a gas.Skills Focus Measuring, Comparingand ContrastingPrep Time 20 minutesMaterials round balloon, 2-L plasticbottle, metric tape measure, plasticbucket, iceAdvance Prep The circumference ofthe balloon can be found by wrappinga string around the balloon and thenmeasuring the length of the string.Class Time 20 minutesSafety Students should wear safetygoggles and lab aprons and must wipeup any spills immediately to avoid falls.Teaching Tips Students can calculate the volume ofthe balloon from its circumferenceby approximating the shape of theballoon as a sphere and using theequation C 2 r to find the radius.4The volume is then given by V 3 r3.Make sure students include the bottleto determine the total volume of theenclosed air.Expected Outcome The ballooncontracts as the air in the bottle cools.Analyze and Conclude1. The volume decreased when cool.2. Cooling the air inside the bottle andballoon reduced the kinetic energy of itsparticles, and therefore the pressure onthe balloon, causing it to contract.Visual, Logical1. Inflate a round balloon andthen stretch its openingover the mouth of a 2-Lbottle. Use a tape measureto measure and record theballoon’s circumference.2. Put a dozen ice cubes intoa plastic bucket. Add coldwater to the bucket to adepth of 15 cm. Submergethe bottom of the bottle inthe ice water and tape thebottle in place.3. After 10 minutes, measureand record the circumference of the balloon.Analyze and ConcludeIf you take a balloon outside on a cold winter day, it shrinks. Can youexplain why? As temperature decreases, the particles that make up theair inside the balloon move more slowly, on average. Slower particlescollide less often and exert less force, so gas pressure decreases and theballoon contracts. This is called thermal contraction.If you bring the balloon inside, it expands. Thermal expansion isan increase in the volume of a material due to a temperature increase.Thermal expansion occurs when particles of matter move fartherapart as temperature increases. Gases expand more than liquids andliquids usually expand more than solids. A gas expands more easilythan a liquid or a solid because the forces of attraction among particles in a gas are weaker.Thermal expansion is used in glass thermometers. As temperatureincreases, the alcohol in the tube expands and its height increases. Theincrease in height is proportional to the increase in temperature. In anoven thermometer, a strip of brass and a strip of steel are bondedtogether and wound up in a coil. As the coil heats up, the two metalsexpand at different rates, and the coil unwinds. This causes the needleto rotate on the temperature scale.1. Observing How didthe volume of air in theballoon change?2. Inferring Explain why theair behaved as it did.What is thermal expansion?Specific HeatWhen a car is heated by the sun, the temperature of the metal doorincreases more than the temperature of the plastic bumper. Do youknow why? One reason is that the iron in the door has a lower specificheat than the plastic in the bumper. Specific heat is the amount of heatneeded to raise the temperature of one gram of a material by one degreeCelsius. If equal masses of iron and plastic absorb the same heat, theiron’s temperature rises more.The lower a material’s specific heat,the more its temperature rises when a given amount of energy isabsorbed by a given mass.Specific heat is often measured in joules per gram perdegree Celsius, or J/g C. Figure 3 gives specific heats forSpecific Heats of Selected Materialsa few common materials. It takes 4.18 joules of energy toMaterial (at 100 kPa)Specific Heat (J/g ⴗC)raise the temperature of 1.00 gram of water by 1.00 degreeWater4.18Celsius. How much energy is needed to heat 2.00 grams ofPlastic (polypropylene)1.84–2.09water to the same temperature? You would have to addAir1.01twice as much energy, or 8.36 joules.Iron0.449Silver0.235476Figure 3 Specific heat is the heat needed to raise the temperature of 1 gram of material by 1ºC. Analyzing Data Whichmaterial in the table has the highest specific heat? The lowest?Chapter 16Facts and FiguresSpecific HeatBuild Science SkillsL2Analyzing Data Have students examinethe specific heat values in Figure 3. Ask,Which substance requires nearly 1 J ofenergy to raise the temperature of 1 gby 1 C? (Air) What amount of energywould be required to raise the temperature of 2.00 g of water by 1.00 C?(4.18 2.00 8.36 J) Logical476 Chapter 16Thermal Contraction One of the fewexceptions to thermal expansion is water nearits freezing point. Over most temperatureranges, water increases in volume as itstemperature increases, but between 0 C and4 C water actually contracts as it gets warmer.This unusual behavior occurs because hydrogen bonding between water molecules in icearranges them in a way that occupies a greatervolume than in liquid water. This results inice being less dense than liquid water. In thewinter, when a pond begins to freeze, thedenser, warmer water sinks to the bottom,and the cooler, less dense ice floats. This formsa layer of warmer water at the bottom of thepond, in which fish are able to live.

0472 hsps09te Ch16.qxp4/19/078:40 AMPage 477Build Math SkillsThe heat (Q) absorbed by a material equals the product of the mass(m), the specific heat (c), and the change in temperature (ΔT).Specific HeatFor: Links on specific heatVisit: www.SciLinks.orgWeb Code: ccn-2161Q m c ΔTL1Formulas and Equations Studentsshould become familiar with rearrangements of the formula Q m c T,so that any one of these quantities canbe calculated in terms of the other three.Have students rearrange the equationin order to calculate specific heatc Q/(m T), mass m Q/(c ΔT),and temperature ΔT Q/(m c).Logical, PortfolioIn this formula, heat is in joules, mass is in grams, specific heat is inJ/g C, and the temperature change is in degrees Celsius.Direct students to the Math Skills inthe Skills and Reference Handbookat the end of the student text foradditional help.Calculating Specific HeatAn iron skillet has a mass of 500.0 grams. The specific heat of ironis 0.449 J/g C. How much heat must be absorbed to raise theskillet’s temperature by 95.0 C?Read and UnderstandWhat information are you given?1. How much heat is needed toraise the temperature of 100.0 gof water by 85.0 C?Mass of iron, m 500.0 gSpecific heat of iron, c 0.449 J/g C2. How much heat is absorbed bya 750-g iron skillet when itstemperature rises from 25 Cto 125 C?Temperature change, ΔT 95.0 CPlan and Solve3. In setting up an aquarium, theheater transfers 1200 kJ of heatto 75,000 g of water. What isthe increase in the water’stemperature? (Hint: Rearrangethe specific heat formula to solvefor ΔT.)What unknown are you trying to calculate?Amount of heat needed, Q ?What formula contains the given quantities andthe unknown?4. To release a diamond fromits setting, a jeweler heats a10.0-g silver ring by adding23.5 J of heat. How muchdoes the temperature of thesilver increase?Q m c ΔTReplace each variable with its known value.Q 500.0 g 0.449 J/g C 95.0 CFor Extra Help5. What mass of water will changeits temperature by 3.0 C when525 J of heat is added to it? 21,375 J 21.4 kJL2Solutions1. Q m c ΔT (100.0 g)(4.18 J/g C)(85.0 C) 35.5 kJ2. Q m c ΔT (750 g)(0.449 J/g C)(125 C 25 C) (750 g)(0.449 J/g C)(100 C) 34 kJ3. ΔT Q/(m c) 1,200,000 J/(75,000 g 4.18 J/g C) 3.8 C4. ΔT Q/(m c) 23.5 J/(10.0 g 0.235 J/g C) 10.0 C5. m Q/(ΔT c) 525 J/(3.0 C 4.18 J/g C) 42 gLogicalLook Back and CheckIs your answer reasonable?Round off the data to give a quick estimate.L1Make sure students start by writingout the equation required to solve eachproblem. Then, check that they are ableto solve the equation for the unknownvariable using basic algebra skills.LogicalQ 500 g 0.5 J/g C 100 C 25 kJThis is close to 21.4 kJ, so the answer is reasonable.Thermal Energy and Heat477Additional Problems1. Gold has a specific heat of 0.13 J/g C. If asample of gold with a mass of 250 g undergoesa temperature increase of 4.0 C, how much heatdoes it absorb? (130 J)2. A piece of iron at a temperature of 145.0 C coolsoff to a temperature of 45.0 C. If the iron has amass of 10.0 g and a specific heat of 0.449 J/g C,how much heat is given up? (449 J)Logical, PortfolioDownload a worksheet on specificheat for students to complete, andfind additional teacher supportfrom NSTA SciLinks.Answer to . . .Figure 3 Silver has the lowestspecific heat. Water has the highestspecific heat.Thermal expansion is theincrease in volume of amaterial due to a temperature increase.Thermal Energy and Heat 477

CalorimeterSection 16.1 (continued)Measuring Heat ChangesStirrerMeasuring HeatChangesCalorimetryThermometerLidL2WaterPurpose Students observe a calorimetermeasuring changes in thermal energy.AluminumsampleMaterials plastic foam cup with lid,thermometer, water, iron bolt ( 75 g)Procedure Place the iron bolt in afreezer for one hour prior to thedemonstration. Fill the cup two-thirds fullwith room-temperature water and recordits temperature. Place the cold iron in thewater and cover the cup. After threeminutes, record the temperature of thewater. Ask what students can infer aboutthe bolt’s initial temperature.Figure 4 A calorimeter is used to measurespecific heat. A sample to be tested is heatedand placed in the calorimeter. The lid is put onand the temperature change is observed.Hypothesizing Why does the calorimeterneed a stirrer?Section 16.1 AssessmentSafety Wipe up spills immediately.Expected Outcome Students shouldconclude that the bolt was colder thanthe water. Visual, GroupReviewing Concepts1.2.3 ASSESSEvaluateUnderstandingL23.Ask students to write a summaryparagraph relating thermal energy,temperature, and heat.ReteachA calorimeter is an instrument used to measure changes inthermal energy.A calorimeter uses the principle that heatflows from a hotter object to a colder object until both reachthe same temperature. According to the law of conservationof energy, the thermal energy released by a test sample is equalto the thermal energy absorbed by its surroundings. Thecalorimeter is sealed to prevent thermal energy from escaping.Figure 4 shows how a calorimeter can be used to measurethe specific heat of aluminum. A known mass of water isadded to the calorimeter. The mass of the sample of aluminumis measured. The aluminum is heated and then placed in thewater. The calorimeter is sealed. As the aluminum cools off,the water is stirred to distribute thermal energy evenly. Thewater heats up until both the aluminum and the water are at thesame temperature. The change in temperature of the water ismeasured. The thermal energy absorbed by the water is calculated using the specific heat equation. Since this same amountof thermal energy was given off by the sample of aluminum,the specific heat of aluminum can be calculated.4.5.L16.Use Figure 2 to summarize key conceptsabout thermal energy.In what direction does heat flow on itsown spontaneously?How is the temperature of an objectrelated to the average kinetic energy ofits particles?Name two variables that affect thethermal energy of an object.What causes thermal expansion of anobject when it is heated?How do the temperature increasesof different materials depend on theirspecific heats?What principle explains how a calorimeteris used to measure the specific heat of asample material?Critical Thinking7. Applying Concepts Why is it necessary tohave regularly spaced gaps between sectionsof a concrete sidewalk?Solutions10. Q m c ΔT (1000.0 g) (0.39 J/g C) (45.0 25.0 C) 7800 J11. ΔT Q/(m c) 18,200 J/(100.0 g) (4.18 J/g C) 43.5 CIf your class subscribesto the Interactive Textbook, use it toreview key concepts in in Section 16.1.Answer to . . .Figure 4 The stirrer keeps temperature uniform.478 Chapter 164788. Predicting An iron spoon and silver spoonhave the same mass. Which becomes hotterwhen both are left in hot tea for one minute?(Hint: Use the specific heats given in Figure 3.)9. Calculating If it takes 80.0 joules to raise thetemperature of a material by 10.0 C, howmuch heat must be added to cause anadditional increase of 20.0 C?10. The specific heat of copper is0.39 J/g C. How much heat is neededto raise the temperature of 1000.0 g ofcopper from 25.0 C to 45.0 C?11. A peanut burned in a calorimetertransfers 18,200 joules to 100.0 g ofwater. What is the rise in the water’stemperature? (Hint: Rearrange thespecific heat formula to solve for T.)Chapter 16Section 16.1Assessment1. Heat flows spontaneously from hot objectsto cold objects.2. Temperature is related to the averagekinetic energy of the particles in an object dueto their random motions through space.3. Mass of the object, temperature4. Particles of matter tend to move fartherapart as temperature increases.5. The lower a material’s specific heat, the moreits temperature increases when equal amountsof thermal energy are added to equal masses.6. A calorimeter uses the principle that heatflows from a hotter object to a colder objectuntil both reach the same temperature.7. The gaps provide space for concrete slabsto expand into so they do not buckle.8. Both spoons absorb the same energyand have the same mass. Because silver has alower specific heat (0.235 J/g C) than iron(0.449 J/g C), the silver becomes hotter.9. Doubling the temperature change doublesthe energy required, so 160 joules mustbe added.

0472 hsps09te Ch16.qxp3/6/071:54 PMPage 479Section 16.216.2 Heat andThermodynamics1 FOCUSObjectivesKey ConceptsWhy is conduction slowerin gases than in liquidsor solids?In what natural cycles doconvection currents occur?How does an object’stemperature affectradiation?What are the three lawsof thermodynamics?Vocabulary conductionthermal conductorthermal insulatorconvectionconvection currentradiationthermodynamicsheat enginewaste heatReading StrategyBuilding Vocabulary Copy the table below.As you read, add definitions and examples tocomplete the table.DefinitionsExamplesConduction: transfer of thermalenergy without transfer of matterFrying panhandle heats up.Convection: a.?b.?Radiation:?d.?c.To bake cookies, you put cookie dough on a baking sheet and pop itin the oven. When the timer goes off, you use oven mitts to pull out thebaking sheet. Why isn’t your bare arm burned by the hot air in the oven?One reason is that air is not a very good conductor of thermal energy.16.2.1 Describe conduction,convection, and radiationand identify which of these isoccurring in a given situation.16.2.2 Classify materials as thermalconductors or thermalinsulators.16.2.3 Apply the law of conservationenergy to conversions betweenthermal energy and otherforms of energy.16.2.4 Apply the second law ofthermodynamics in situationswhere thermal energy movesfrom cooler to warmer objects.16.2.5 State the third law ofthermodynamics.Reading FocusConductionConduction is the transfer of thermal energy with no overall transferof matter. Conduction occurs within a material or between materialsthat are touching. To understand conduction, look at the Newton’scradle in Figure 5. When a ball is pulled back and released, you mightexpect all of the balls to move to the right after the impact. Instead,most of the kinetic energy is transferred to one ball on the end. Similarly,in conduction, collisions between particles transfer thermal energy,without any overall transfer of matter.Recall that forces are weak among particles ina gas. Compared to liquids and solids, the particlesin gases are farther apart.Conduction in gasesis slower than in liquids and solids because theparticles in a gas collide less often. In most solids,conduction occurs as particles vibrate in place andpush on each other. In metals, conduction is fasterbecause some electrons are free to move about.These free electrons collide with one another andwith atoms or ions to transfer thermal energy.Build VocabularyFigure 5 Conduction is thetransfer of thermal energywithout transferring matter. Thisdevice, called Newton’s cradle,helps to visualize conduction.After one ball strikes the rest,most of the kinetic energy istransferred to one ball on the end.L2Word-Part Analysis Ask studentswhat words they know that have the keyword parts therm, con, duct, and radia.(Thermal energy, conductor, and radiator)Give a definition of a word part. (Thermmeans “heat,” con means “with,” ductmeans “to lead,” and radia means“rays.”) Give additional examples thatshare the word parts in question.(Thermometer, contact, deduct, radio)Reading StrategyL2a. The transfer of thermal energy by themovement of particles in a fluid b. Hotair circulates in an oven. c. The transfer ofenergy by waves moving through spaced. Heating coil of an electric stove glows.Thermal Energy and Heat4792 INSTRUCTConductionUse VisualsSection ResourcesPrint Laboratory Manual, Investigations 16Aand 16B Reading and Study Workbook WithMath Support, Section 16.2 Transparencies, Section 16.2Technology Interactive Textbook, Section 16.2 Presentation Pro CD-ROM, Section 16.2 Go Online, NSTA SciLinks, ThermodynamicsL1Figure 5 Use the Newton’s cradle toreinforce why energy is transferred moreefficiently by conduction in a liquid orsolid. Ask, How could the balls bearranged to demonstrate conductionin a gas? (The balls could be detachedand spread on a table. When one ball isrolled toward any of the others, collisionswould occur only occasionally and withoutorder.)VisualThermal Energy and Heat 479PPLS

Section 16.2 (continued)Conductors andInsulatorsThermal Conductors Figure 6 shows a frying pan on a hotL2Purpose To show the similarities anddifferences between types of thermalconductors and insulators.Materials a block of wood, analuminum pie plate, a metal spoon,a plastic spoon, a silk or cotton handkerchief, a metal screwdriverProcedure Place the objects on a windowsill that is well-exposed to sunlight.Leave half of each object lying in thesunlight and the other half lying in theshade. Place the screwdriver so that thehalf of the metal shaft nearest the handleis in the shade. Leave the objects in thesunlight for at least 30 minutes. Haveeach student pick up each object by theend that has been in shade. Have themnote carefully any difference betweenthe temperatures of the two ends ofeach object.Safety Remind students that the partsof the objects that have been in sunlightmay be very hot.Expected Outcome The pie plate, themetal spoon, and the shaft of the screwdriver are all metals, and so are goodthermal conductors. The parts of theseobjects that have been in the shadeshould feel warm. The wood, handkerchief, plastic spoon, and handle of thescrewdriver are thermal insulators, andshould not feel very warm.Kinesthetic, GroupFigure 6 The arrows show howthermal energy is conducted awayfrom the heat source in a metalfrying pan. Predicting Would itbe safe to touch the handle ofthe wooden spoon?stove. The bottom of the pan heats up first. The metal handle heats uplast. You can see that the flames do not directly heat the handle. Thehandle heats up because the metal is a good thermal conductor.A thermal conductor is a material that conducts thermal energywell. A wire rack in a hot oven can burn you because the metal conducts thermal energy so quickly. Pots and pans often are made ofcopper or aluminum because these are good conductors.A thermal conductor doesn’t have to be hot. Why does a tile floorfeel colder than a wooden floor? Both floors are at room temperature.But the tile feels colder because it is a better conductor and transfersthermal energy rapidly away from your skin.Thermal Insulators Why is it safe to pick up the wooden spoonshown in Figure 6? Wood heats up slowly because it is a poor conductor of thermal energy. A material that conducts thermal energy poorlyis called a thermal insulator.Air is a very good insulator. A double-pane window has an air spacecontained between two panes of glass. The air slows down conductionto reduce heat loss in winter and to keep heat out of a building insummer. More expensive windows use argon gas, which is an even betterinsulator than air. Wool garments and plastic foam cups are two moreexamples of insulators that use trapped air to slow down conduction.Figure 7 Convection is thetransfer of thermal energy by themovement of particles in a fluid.A Passing sandbags along a line islike transferring thermal energyby convection.B The arrows show convectionof air in an oven.Predicting Which part of theoven should have the highesttemperature?ConvectionConvection is the transfer of thermal energy when particles of a fluidmove from one place to another. Look at the people building a wallwith sandbags in Figure 7A. The moving sandbags are like the particlesin a fluid. The wall grows taller as more

of matter. 474 Chapter 16 FOCUS Objectives 16.1.1 Explain how heat and work transfer energy. 16.1.2 Relate thermal energy to the motion of particles that make up a material. 16.1.3 Relate temperature to thermal energy and to thermal expansion. 16.1.4 Calculate thermal energy, temp