Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Hewitt/Lyons/Suchocki/Yeh Conceptual Integrated Science Chapter 6 HEAT

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley This lecture will help you understand: The Kinetic Theory of Matter Temperature Absolute Zero What Is Heat? Quantity of Heat The Laws of Thermodynamics Entropy Specific Heat Capacity Thermal Expansion Expansion of Water Heat Transfer: Conduction Heat Transfer: Convection Heat Transfer: Radiation Emission of Radiant Energy Absorption of Radiant Energy

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley The Kinetic Theory of Matter Kinetic Theory of Matter: Matter is made up of tiny particles (atoms or molecules) that are always in motion. Thermal Energy: The total energy (kinetic and potential) of the submicroscopic particles that make up a substance.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Temperature is defined as the measure of hotness or coldness of an object (degrees Celsius, or degrees Fahrenheit, or kelvins). is related to the average translational kinetic energy per molecule in a substance.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Temperature Thermometer is an instrument that measures temperature by comparing the expansion and contraction of a liquid as it gains or loses thermal energy. Infrared thermometer measures temperature by the radiation a substance emits.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Temperature Temperature has no upper limit. Temperature of a substance is registered on a liquid-base thermometer when the substance has reached thermal equilibrium with the thermometer.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Temperature Three different temperature scales differ in zero point and divisions: Celsius scale freezing point of water: 0  C boiling point of water: 100  C division: 100 degree units

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Temperature Fahrenheit scale freezing point of water: 32  F boiling point of water: 212  F division: 180 degree units Kelvin scale (used in scientific research) freezing point of water: 273 K boiling point of water: 373 K division: same-size increments as Celsius scale

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley There is twice as much molecular kinetic energy in 2 liters of boiling water as in 1 liter of boiling water. Which will be the same for both? A.Temperature. B.Thermal energy. C.Both of the above. D.None of the above. Temperature CHECK YOUR NEIGHBOR

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley There is twice as much molecular kinetic energy in 2 liters of boiling water as in 1 liter of boiling water. Which will be the same for both? A.Temperature. B.Thermal energy. C.Both of the above. D.None of the above. Explanation: Average kinetic energy of molecules is the same, which means temperature is the same for both. Temperature CHECK YOUR ANSWER

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Absolute Zero Absolute zero or zero K is the lowest limit of temperature at – 273  C where molecules have lost all available kinetic energy. A substance cannot get any colder.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley What Is Heat? Heat is defined as a flow of thermal energy due to a temperature difference. The direction of heat flow is from a higher-temperature substance to a lower-temperature substance.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley If a red hot thumbtack is immersed in warm water, the direction of heat flow will be from the A.warm water to the red hot thumbtack. B.red hot thumbtack to the warm water. C.no heat flow. D.not enough information. What Is Heat? CHECK YOUR NEIGHBOR

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley If a red hot thumbtack is immersed in warm water, the direction of heat flow will be from the A.warm water to the red hot thumbtack. B.red hot thumbtack to the warm water. C.no heat flow. D.not enough information. What Is Heat? CHECK YOUR ANSWER

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Quantity of Heat Heat is measured in units of energy—joules or calories. calorie is defined as the amount of heat needed to raise the temperature of 1 gram of water by 1 Celsius degree joules = 1 calorie so 4.18 joules of heat will change that temperature of 1 gram of water by 1 Celsius degree.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Quantity of Heat Energy rating of food and fuel is measured by energy released when they are metabolized. Kilocalorie: Heat unit for labeling food One kilocalorie or Calorie (with a capital C) is the heat needed to change the temperature of 1 kilogram of water by 1 degree Celsius.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley The same quantity of heat is added to different amounts of water in two equal-size containers. The temperature of the smaller amount of water A.decreases more. B.increases more. C.does not change. D.not enough information. Quantity of Heat CHECK YOUR NEIGHBOR

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley The same quantity of heat is added to different amounts of water in two equal-size containers. The temperature of the smaller amount of water A.decreases more. B.increases more. C.does not change. D.not enough information. Quantity of Heat CHECK YOUR ANSWER

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley You heat a half-cup of tea and its temperature rises by 4  C. How much will the temperature rise if you add the same amount of heat to a full cup of tea? A.0  C. B.2  C. C.4  C. D.8  C. Quantity of Heat CHECK YOUR NEIGHBOR

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley You heat a half-cup of tea and its temperature rises by 4  C. How much will the temperature rise if you add the same amount of heat to a full cup of tea? A.0  C. B.2  C. C.4  C. D.8  C. Quantity of Heat CHECK YOUR ANSWER

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley The Laws of Thermodynamics First Law of Thermodynamics: Whenever heat flows into or out of a system, the gain or loss of thermal energy equals the amount of heat transferred. When thermal energy transfers as heat, it does so without net loss or gain.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley The Laws of Thermodynamics Second Law of Thermodynamics: Heat never spontaneously flows from a lower-temperature substance to a higher- temperature substance. Heat can be made to flow the opposite way only when work is done on the system or by adding energy from another source.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley The Laws of Thermodynamics Third Law of Thermodynamics: No system can reach absolute zero.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley When work is done on a system, compressing air in a tire pump, for example, the temperature of the system A.increases. B.decreases. C.remains unchanged. D.is no longer evident. The Laws of Thermodynamics CHECK YOUR NEIGHBOR

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley When work is done on a system, compressing air in a tire pump, for example, the temperature of the system A.increases. B.decreases. C.remains unchanged. D.is no longer evident. Explanation: In accord with the first law of thermodynamics, work input increases the energy of the system. The Laws of Thermodynamics CHECK YOUR ANSWER

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Entropy is a measure of the disorder of a system. Whenever energy freely transforms from one form to another, the direction of transformation is toward 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 Wesley Entropy Second law of thermodynamics — restatement: Natural systems tend to disperse from concentrated and organized-energy states toward diffuse and disorganized states. Energy tends to degrade and disperse with time. The total amount of entropy in any system tends to increase with time.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Your room gets messier each week. In this case, the entropy of your room is A.increasing. B.decreasing. C.hanging steady. D.nonexistent. Entropy CHECK YOUR NEIGHBOR

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Your room gets messier each week. In this case, the entropy of your room is A.increasing. B.decreasing. C.hanging steady. D.nonexistent. Comment: If your room became more organized each week, then entropy would decrease in proportion to the effort expended. Entropy CHECK YOUR ANSWER

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Specific Heat Capacity Specific heat capacity is defined as the quantity of heat required to change the temperature of 1 unit mass of a substance by 1 degree Celsius. thermal inertia that indicates the resistance of a substance to a change in temperature. sometimes called specific heat.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Which has the higher specific heat, water or land? A.Water. B.Land. C.Both of the above are the same. D.None of the above. Specific Heat CHECK YOUR NEIGHBOR

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Which has the higher specific heat, water or land? A.Water. B.Land. C.Both of the above are the same. D.None of the above. Explanation: A substance with small temperature changes for large heat changes has a high specific heat capacity. Water takes much longer to heat up in the sunshine than does land. This difference is a major influence on climate. Specific Heat CHECK YOUR ANSWER

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Thermal Expansion When the temperature of a substance is increased, its particles jiggle faster and move farther apart. All forms of matter generally expand when heated and contract when cooled.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley When stringing telephone lines between poles in the summer, it is advisable to allow the lines to A.sag. B.be taut. C.be close to the ground. D.allow ample space for birds. Thermal Expansion CHECK YOUR NEIGHBOR

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley When stringing telephone lines between poles in the summer, it is advisable to allow the lines to A.sag. B.be taut. C.be close to the ground. D.allow ample space for birds. Explanation: Telephone lines are longer in a warmer summer and shorter in a cold winter. Hence, they sag more on hot summer days than in winter. If the lines are not strung with enough sag in summer, they might contract too much and snap during the winter—especially when carrying ice. Thermal Expansion CHECK YOUR ANSWER

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Expansion of Water When water becomes ice, it expands. Ice has open-structured crystals resulting from strong bonds at certain angles that increase its volume. This make ice less dense than water.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Expansion of Water Water between 0  C and 4  C does not expand with temperature. As the temperature of 0  water rises, it contracts until it reaches 4  C. Thereafter, it expands. Water is at its smallest volume and greatest density at 4  C. When 0  C water freezes to become ice, however, it has its largest volume and lowest density.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Expansion of Water Volume changes for a 1-gram sample of water.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley When a sample of 0  C water is heated, it first A.expands. B.contracts. C.remains unchanged. D.not enough information. Expansion of Water CHECK YOUR NEIGHBOR

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley When a sample of 0  C water is heated, it first A.expands. B.contracts. C.remains unchanged. D.not enough information. Explanation: Water continues to contract until it reaches a temperature of 4  C. With further increase in temperature beyond 4  C, water then expands. Expansion of Water CHECK YOUR ANSWER

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley When a sample of 4  C water is cooled, it A.expands. B.contracts. C.remains unchanged. D.not enough information. Expansion of Water CHECK YOUR NEIGHBOR

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley When a sample of 4  C water is cooled, it A.expands. B.contracts. C.remains unchanged. D.not enough information. Explanation: Parts of the water will crystallize and occupy more space. Expansion of Water CHECK YOUR ANSWER

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Heat Transfer Processes of thermal energy transfer: conduction convection radiation

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Heat Transfer: Conduction Conduction occurs predominately in solids where the molecules remain in relatively restricted locations.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Heat Transfer: Conduction Example: When one end of a solid is placed near a heat source, electrons and adjacent molecules gain kinetic energy and start to move faster and farther. They collide with neighboring molecules and transfer some of their kinetic energy to them. These molecules then interact with other neighboring molecules, and thermal energy is gradually transferred along the solid.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Heat Transfer: Conduction Good conductors: composed of atoms with “loose” outer electrons known as poor insulators examples—all metals to varying degrees Poor conductors: delay the transfer of heat known as good insulators examples—wood, wool, straw, paper, cork, Styrofoam, liquid, gases, air, or materials with trapped air

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Heat Transfer: Conduction No insulator can totally prevent heat from getting through it. An insulator reduces the rate at which heat penetrates.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley If you hold one end of a metal bar against a piece of ice, the end in your hand will soon become cold. Does cold flow from the ice to your hand? A.Yes. B.In some cases, yes. C.No. D.In some cases, no. Heat Transfer: Conduction CHECK YOUR NEIGHBOR

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley If you hold one end of a metal bar against a piece of ice, the end in your hand will soon become cold. Does cold flow from the ice to your hand? A.Yes. B.In some cases, yes. C.No. D.In some cases, no. Explanation: Cold does not flow from the ice to your hand. Heat flows from your hand to the ice. The metal is cold to your touch, because you are transferring heat to the metal. Heat Transfer: Conduction CHECK YOUR ANSWER

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Heat Transfer: Convection Convection: occurs in liquids and gases involves the movement of warmer gases or liquids to cooler surroundings Two characteristics of convection: the ability of flow—carrying thermal energy with the fluid the ability of warm fluid to rise in cooler surroundings

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Although warm air rises, why are mountaintops cold and snow covered, while the valleys below are relatively warm and green? A.Warm air cools when rising. B.There is a thick insulating blanket of air above valleys. C.Both of the above. D.None of the above. Heat Transfer: Convection CHECK YOUR NEIGHBOR

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Although warm air rises, why are mountaintops cold and snow covered, while the valleys below are relatively warm and green? A.Warm air cools when rising. B.There is a thick insulating blanket of air above valleys. C.Both of the above. D.None of the above. Explanation: Earth’s atmosphere acts as a blanket, which for one important thing, keeps Earth from freezing at nighttime. Heat Transfer: Convection CHECK YOUR ANSWER

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Heat Transfer: Radiation Radiation is the process by which thermal energy is transferred by electromagnetic waves. A thermal energy source such as the Sun converts some of its energy into electromagnetic waves. These waves carry energy, which converts back into thermal energy when absorbed by a receiver. The energy source radiates energy, and a receiver absorbs it.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Heat Transfer: Radiation Wavelength of radiation is related to the frequency of vibration. Low - frequency vibrations  long waves High - frequency vibrations  short waves

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Emission of Radiant Energy All substances at any temperature above absolute zero emit radiant energy. Average frequency ( ) of radiant energy is directly proportional to the absolute temperature T of the emitter:  T

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley If a good absorber of radiant energy were a poor emitter, its temperature compared with its surroundings would be A.lower. B.higher. C.unaffected. D.none of the above. Emission of Radiant Energy CHECK YOUR NEIGHBOR

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley If a good absorber of radiant energy were a poor emitter, its temperature compared with its surroundings would be A.lower. B.higher. C.unaffected. D.none of the above. Explanation: If a good absorber were not also a good emitter, there would be a net absorption of radiant energy, and the temperature of a good absorber would remain higher than the temperature of the surroundings. Nature is not so! Emission of Radiant Energy CHECK YOUR ANSWER

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Absorption of Radiant Energy Absorption of Radiant Energy: The ability to absorb and radiate thermal energy is indicated by the color of the material. Good absorbers and good emitters are dark in color. Poor absorbers and poor emitters are reflective or light in color.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Absorption of Radiant Energy The surface of any material both absorbs and emits radiant energy. When a surface absorbs more energy than it emits, it is a net absorber, and temperature rises. When a surface emits more energy than it absorbs, it is a net emitter, and temperature falls.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Absorption of Radiant Energy Whether a surface is a net absorber or net emitter depends on whether its temperature is above or below that of its surroundings. A surface hotter than its surroundings will be a net emitter and will cool. A surface colder than its surroundings will be a net absorber and will warm.

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Which melts faster in sunshine—dirty snow or clean snow? A.Dirty snow. B.Clean snow. C.Both of the above. D.None of the above. Absorption of Radiant Energy CHECK YOUR NEIGHBOR

Copyright © 2007 Pearson Education, Inc., publishing as Pearson Addison Wesley Which melts faster in sunshine—dirty snow or clean snow? A.Dirty snow. B.Clean snow. C.Both of the above. D.None of the above. Explanation: Dirty snow absorbs more sunlight, whereas clean snow reflects more. Absorption of Radiant Energy CHECK YOUR ANSWER