The Kinetic Theory Of Matter

The Kinetic Theory of MatterHewitt/Lyons/Suchocki/YehConceptual IntegratedScienceChapter 6HEATCopyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyTemperatureTemperatureis defined as the measure ofhotness or coldness of anobject (degrees Celsius, ordegrees Fahrenheit, or kelvins).Temperature is related to theaverage translational kineticenergy per molecule in asubstance.Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyTemperatureTemperature has no upper limit.Temperature of a substance is registered on aliquid-base thermometer when the substance hasreached thermal equilibrium with the thermometer.Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyKinetic Theory of Matter:Matter is made up of tiny particles (atoms ormolecules) that are always in motion.Thermal Energy:The total energy (kinetic and potential) of thesubmicroscopic particles that make up asubstance.Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyTemperatureA Thermometer is an instrument that measurestemperature by comparing the expansion andcontraction of a liquid as it gains or loses thermalenergy.An infrared thermometer measures temperature bythe radiation a substance emits.Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyTemperatureThree different temperature scales differ in zeropoint and divisions: Celsius scalefreezing point of water: 0 Cboiling point of water: 100 Cdivision: 100 degree unitsCopyright 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley1

Temperature Fahrenheit scalefreezing point of water: 32 Fboiling point of water: 212 Fdivision: 180 degree unitsCopyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyAbsolute ZeroAbsolute zero or zero K is the lowest limit oftemperature at –273 C where molecules havelost all available kinetic energy.A substance cannot get any colder.Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyQuantity of HeatHeat is measured in units of energy—joules orcalories.The calorie is defined as the amount of heat neededto raise the temperature of 1 gram of water by 1Celsius degree.4.18 joules 1 calorieTemperature Kelvin scale (used in scientificresearch)freezing point of water: 273 Kboiling point of water: 373 Kdivision: same-size incrementsas Celsius scaleCopyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyWhat Is Heat?Heat is defined as a flow of thermal energy due toa temperature difference.The direction of heat flow is from a highertemperature substance to a lower-temperaturesubstance.Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyQuantity of HeatEnergy rating of food and fuel is measured byenergy released when they are metabolized.Kilocalorie: Heat unit for labeling foodOne kilocalorie or Calorie (with a capital C) isthe heat needed to change the temperature of1 kilogram of water by 1 degree Celsius.so 4.18 joules of heat will change the temperature of1 gram of water by 1 Celsius degree.Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyCopyright 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley2

The Laws of ThermodynamicsThe Laws of ThermodynamicsFirst Law of Thermodynamics:Whenever heat flows into or out of a system, thegain or loss of thermal energy equals theamount of heat transferred.Second Law of Thermodynamics:Heat never spontaneously flows from a lowertemperature substance to a higher-temperaturesubstance.When thermal energy transfers as heat, it does sowithout net loss or gain.Heat can be made to flow the opposite way onlywhen work is done on the system or by addingenergy from another source.Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyCopyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyThe Laws of ThermodynamicsThird Law of Thermodynamics:No system can reach absolute zero.EntropyEntropy is a measure of the disorder of a system.Whenever energy freely transforms from oneform to another, the direction of transformation istoward a state of greater disorder and,therefore, toward one of greater entropy.The greater the disorder the higher the entropy.Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyEntropySecond law of thermodynamics — restatement:Natural systems tend to disperse fromconcentrated and organized-energy statestoward diffuse and disorganized states.Energy tends to degrade and disperse with time.The total amount of entropy in any system tends toincrease with time.Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyCopyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleySpecific Heat CapacitySpecific heat capacity is defined as the quantity of heat required to change thetemperature of 1 unit mass of a substance by 1degree Celsius. thermal inertia that indicates the resistance of asubstance to a change in temperature.Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley3

Thermal ExpansionWhen the temperature of a substance isincreased, its particles jiggle faster and movefarther apart.Expansion of WaterWhen water becomes ice, it expands. Ice has openstructured crystals resulting from strong bonds atcertain angles that increase its volume. This makeice less dense than water.All forms of matter generally expand when heatedand contract when cooled.Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyExpansion of WaterWater between 0 C and 4 C does not expand withtemperature. As the temperature of 0 waterrises, it contracts until it reaches 4 C. Thereafter,it expands.Water is at its smallest volume and greatestdensity at 4 C. When 0 C water freezes tobecome ice, however, it has its largest volumeand lowest density.Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyHeat TransferCopyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyExpansion of WaterVolume changes for a 1-gram sample of water.Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyHeat Transfer: ConductionProcesses of thermal energy transfer: conduction convection radiationConduction occurs predominately in solids wherethe molecules remain in relatively restrictedlocations.Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyCopyright 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley4

Heat Transfer: ConductionHeat Transfer: ConductionExample of conduction:a) When one end of a solid is placed near a heat source,electrons and adjacent molecules gain kinetic energyand start to move faster and farther.b) They collide with neighboring molecules and transfersome of their kinetic energy to them.c) These molecules then interact with other neighboringmolecules, and thermal energy is gradually transferredalong the solid.Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyHeat Transfer: ConductionGood conductors are composed of atoms with “loose” outer electrons known as poor insulators examples—all metals to varying degreesCopyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyHeat Transfer: ConductionNo insulator can totally prevent heat from gettingthrough it.An insulator reduces the rate at which heatpenetrates.Poor conductors: delay the transfer of heat known as good insulators examples—wood, wool, straw, paper, cork,Styrofoam, liquid, gases, air, or materials with trappedairCopyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyHeat Transfer: ConvectionConvection: occurs in liquids and gases involves the movement of warmer gases or liquids tocooler surroundingsCopyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyCopyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyHeat Transfer: ConvectionTwo characteristics of convection: the ability of flow—carrying thermal energy with thefluid the ability of warm fluid to rise in cooler surroundingsCopyright 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley5

Heat Transfer: RadiationRadiation is the process by which thermal energy istransferred by electromagnetic waves.Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyHeat Transfer: RadiationThe wavelength of radiation is related to thefrequency of vibration.Low-frequency vibrations long wavesHigh-frequency vibrations short wavesCopyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyAbsorption of Radiant EnergyThe ability to absorb and radiate thermal energy isindicated by the color of the material.Good absorbers and goodemitters are dark in color.Poor absorbers and pooremitters are reflective orlight in color.Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyHeat Transfer: RadiationA thermal energy source such as the Sun convertssome of its energy into electromagnetic waves.These waves carry energy, which converts back intothermal energy when absorbed by a receiver. Theenergy source radiates energy, and a receiverabsorbs it.Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyEmission of Radiant EnergyEmission of Radiant EnergyAll substances at any temperature aboveabsolute zero emit radiant energy.Average frequency ( ) of radiant energy isdirectly proportional to the absolutetemperature T of the emitter: TCopyright 2007 Pearson Education, Inc., publishing as Pearson Addison WesleyAbsorption of Radiant EnergyThe surface of any material both absorbs and emitsradiant energy.When a surface absorbs more energy than it emits, itis a net absorber, and temperature rises.When a surface emits more energy than it absorbs, itis a net emitter, and temperature falls.Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley6

Absorption of Radiant EnergyWhether a surface is a net absorber or net emitterdepends on whether its temperature is above orbelow that of its surroundings.A surface hotter than its surroundings will be a netemitter and will cool.A surface colder than its surroundings will be a netabsorber and will warm.Copyright 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley7

electrons and adjacent molecules gain kinetic energy and start to move faster and farther. b) They collide with neighboring molecules and transfer some of their kinetic energy to them. c) These molecules then interact with other nei