Heat © 2013 Pearson Education, Inc.

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 © 2013 Pearson Education, Inc.

The 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. © 2013 Pearson Education, Inc.

Temperature Temperature is 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. © 2013 Pearson Education, Inc.

Temperature A thermometer is an instrument that measures temperature by comparing the expansion and contraction of a liquid as it gains or loses thermal energy. An infrared thermometer measures temperature by the radiation a substance emits. © 2013 Pearson Education, Inc.

Temperature Temperature has no upper limit. The temperature of a substance is registered on a liquid-base thermometer when the substance has reached thermal equilibrium with the thermometer. © 2013 Pearson Education, Inc.

Temperature Three 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 © 2013 Pearson Education, Inc.

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 © 2013 Pearson Education, Inc.

Temperature CHECK YOUR NEIGHBOR There is twice as much molecular kinetic energy in 2 liters of boiling water as in 1 liter of boiling water. Which is the same for both? Temperature Thermal energy Both temperature and thermal energy Neither temperature nor thermal energy Explain your answer to your neighbor. A. Temperature. © 2013 Pearson Education, Inc.

Temperature CHECK YOUR ANSWER There is twice as much molecular kinetic energy in 2 liters of boiling water as in 1 liter of boiling water. Which is the same for both? Temperature Thermal energy Both temperature and thermal energy Neither temperature nor thermal energy Explanation: The average kinetic energy of the molecules is the same, which means that the temperature is the same for both. A. Temperature. © 2013 Pearson Education, Inc.

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. © 2013 Pearson Education, Inc.

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. © 2013 Pearson Education, Inc.

What Is Heat? CHECK YOUR NEIGHBOR If a red-hot thumbtack is immersed in warm water, the direction of heat flow will be from the warm water to the red-hot thumbtack. red-hot thumbtack to the warm water. There is no heat flow. There is not enough information. Explain your answer to your neighbor. B. red hot thumbtack to the warm water. © 2013 Pearson Education, Inc.

What Is Heat? CHECK YOUR ANSWER If a red-hot thumbtack is immersed in warm water, the direction of heat flow will be from the warm water to the red-hot thumbtack. red-hot thumbtack to the warm water. There is no heat flow. There is not enough information. B. red hot thumbtack to the warm water. © 2013 Pearson Education, Inc.

Quantity of Heat Heat is measured in units of energy—joules or calories. A calorie is defined as the amount of heat needed to raise the temperature of 1 gram of water by 1 Celsius degree. 4.19 joules = 1 calorie so 4.19 joules of heat will change the temperature of 1 gram of water by 1 Celsius degree. © 2013 Pearson Education, Inc.

Quantity of Heat The energy rating of food and fuel is measured by the energy released when they are metabolized. The heat unit for labeling food is the kilocalorie. 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. © 2013 Pearson Education, Inc.

Quantity of Heat CHECK YOUR NEIGHBOR 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 decreases more. increases more. does not change. There is not enough information. Explain your answer to your neighbor. B. increases more. © 2013 Pearson Education, Inc.

Quantity of Heat CHECK YOUR ANSWER 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 decreases more. increases more. does not change. There is not enough information. B. increases more. © 2013 Pearson Education, Inc.

Quantity of Heat CHECK YOUR NEIGHBOR 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? 0C 2C 4C 8C Explain your answer to your neighbor. B. 2C. © 2013 Pearson Education, Inc.

Quantity of Heat CHECK YOUR ANSWER 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? 0C 2C 4C 8C B. 2C. © 2013 Pearson Education, Inc.

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 with no net loss or gain. © 2013 Pearson Education, Inc.

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 when energy is added from another source. © 2013 Pearson Education, Inc.

The Laws of Thermodynamics Third law of thermodynamics: No system can reach absolute zero. © 2013 Pearson Education, Inc.

The Laws of Thermodynamics CHECK YOUR NEIGHBOR When work is done on a system–compressing air in a tire pump, for example–the temperature of the system increases. decreases. remains unchanged. is no longer evident. Explain your answer to your neighbor. A. increases. © 2013 Pearson Education, Inc.

The Laws of Thermodynamics CHECK YOUR ANSWER When work is done on a system–compressing air in a tire pump, for example–the temperature of the system increases. decreases. remains unchanged. is no longer evident. Explanation: In accord with the first law of thermodynamics, work input increases the energy of the system. A. increases. © 2013 Pearson Education, Inc.

Entropy Entropy is a measure of the disorder of a system. Whenever energy freely transforms from one form into another, the direction of transformation is toward a state of greater disorder and, therefore, toward one of greater entropy. Greater disorder  higher entropy © 2013 Pearson Education, Inc.

Entropy Second law of thermodynamics — a 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. © 2013 Pearson Education, Inc.

Entropy CHECK YOUR NEIGHBOR Your room gets messier each week. In this case, the entropyof your room is increasing. decreasing. hanging steady. nonexistent. Explain your answer to your neighbor. A. increasing. © 2013 Pearson Education, Inc.

Entropy CHECK YOUR ANSWER Your room gets messier each week. In this case, the entropy of your room is increasing. decreasing. hanging steady. nonexistent. Comment: If your room became more organized each week, then entropy would decrease in proportion to the effort expended. A. increasing. © 2013 Pearson Education, Inc.

Specific Heat Capacity The specific heat capacity is the quantity of heat required to change the temperature of 1 unit mass of a substance by 1 degree Celsius. Specific heat capacity is thermal inertia that indicates the resistance of a substance to a change in temperature. sometimes called specific heat. © 2013 Pearson Education, Inc.

Specific Heat Capacity CHECK YOUR NEIGHBOR Which has a higher specific heat capacity: water or land? Water Land Both of the above are the same. None of the above Explain your answer to your neighbor. A. Water. © 2013 Pearson Education, Inc.

Specific Heat Capacity CHECK YOUR ANSWER Which has a higher specific heat capacity: water or land? Water Land Both of the above are the same. 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 has a major influence on climate. A. Water. © 2013 Pearson Education, Inc.

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. © 2013 Pearson Education, Inc.

Thermal Expansion CHECK YOUR NEIGHBOR When telephone lines are strung between poles in the summer, it is advisable for the lines to sag. be taut. be close to the ground. allow ample space for birds. Explain your answer to your neighbor. A. sag. © 2013 Pearson Education, Inc.

Thermal Expansion CHECK YOUR ANSWER When telephone lines are strung between poles in the summer, it is advisable for the lines to sag. be taut. be close to the ground. allow ample space for birds. Explanation: Telephone lines are longer in a warm summer and shorter in a cold winter. Hence, they sag more on hot summer days than during the winter. If the lines are not strung with enough sag in the summer, they might contract too much and snap during the winter—especially when they are covered with ice. A. sag. © 2013 Pearson Education, Inc.

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. © 2013 Pearson Education, Inc.

Expansion of Water Water between 0C and 4C does not expand with temperature. As the temperature of 0 water rises, the water 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. © 2013 Pearson Education, Inc.

Expansion of Water Volume changes for a 1-gram sample of water: © 2013 Pearson Education, Inc.

Expansion of Water CHECK YOUR NEIGHBOR When a sample of 0C water is heated, it first expands. contracts. remains unchanged. There is not enough information. Explain your answer to your neighbor. B. contracts. © 2013 Pearson Education, Inc.

Expansion of Water CHECK YOUR ANSWER When a sample of 0C water is heated, it first expands. contracts. remains unchanged. There is 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. B. contracts. © 2013 Pearson Education, Inc.

Expansion of Water CHECK YOUR NEIGHBOR When a sample of 4C water is cooled, it expands. contracts. remains unchanged. There is not enough information. Explain your answer to your neighbor. A. expands. © 2013 Pearson Education, Inc.

Expansion of Water CHECK YOUR ANSWER When a sample of 4C water is cooled, it expands. contracts. remains unchanged. There is not enough information. Explanation: Parts of the water will crystallize and occupy more space. A. expands. © 2013 Pearson Education, Inc.

Heat Transfer Processes of thermal energy transfer: Conduction Convection Radiation © 2013 Pearson Education, Inc.

Heat Transfer: Conduction Conduction occurs predominately in solids where the molecules remain in relatively restricted locations. © 2013 Pearson Education, Inc.

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. © 2013 Pearson Education, Inc.

Heat Transfer: Conduction Good conductors are composed of atoms with "loose" outer electrons. are known as poor insulators. Examples: all metals to varying degrees. Poor conductors delay the transfer of heat. are known as good insulators. Examples: wood, wool, straw, paper, cork, Styrofoam, liquid, gases, air or materials with trapped air © 2013 Pearson Education, Inc.

Heat Transfer: Conduction No insulator can totally prevent heat from getting through it. An insulator reduces the rate at which heat penetrates. © 2013 Pearson Education, Inc.

Heat Transfer: Conduction CHECK YOUR NEIGHBOR 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? Yes In some cases, yes No In some cases, no Explain your answer to your neighbor. C. No. © 2013 Pearson Education, Inc.

Heat Transfer: Conduction CHECK YOUR ANSWER 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? Yes In some cases, yes No 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. C. No. © 2013 Pearson Education, Inc.

Heat Transfer: 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 © 2013 Pearson Education, Inc.

Heat Transfer: Convection CHECK YOUR NEIGHBOR Although warm air rises, why are mountaintops cold and snow covered, while the valleys below are relatively warm and green? Warm air cools when it rises. There is a thick insulating blanket of air above valleys. Both of the above None of the above Explain your answer to your neighbor. C. Both of the above. © 2013 Pearson Education, Inc.

Heat Transfer: Convection CHECK YOUR ANSWER Although warm air rises, why are mountaintops cold and snow covered, while the valleys below are relatively warm and green? Warm air cools when it rises. There is a thick insulating blanket of air above valleys. Both of the above. None of the above. Explanation: Earth's atmosphere acts like a blanket, which keeps Earth from freezing at nighttime. C. Both of the above. © 2013 Pearson Education, Inc.

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. © 2013 Pearson Education, Inc.

Heat Transfer: Radiation The wavelength of radiation is related to the frequency of vibration. Low-frequency vibrations  long waves High-frequency vibrations  short waves © 2013 Pearson Education, Inc.

Emission of Radiant Energy All substances at any temperature above absolute zero emit radiant energy. The average frequency ( ) of radiant energy is directly proportional to the absolute temperature T of the emitter:  T © 2013 Pearson Education, Inc.

Emission of Radiant Energy CHECK YOUR NEIGHBOR If a good absorber of radiant energy were a poor emitter, its temperature compared with its surroundings would be lower. higher. unaffected. none of the above Explain your answer to your neighbor. B. higher. © 2013 Pearson Education, Inc.

Emission of Radiant Energy CHECK YOUR ANSWER If a good absorber of radiant energy were a poor emitter, its temperature compared with its surroundings would be lower. higher. unaffected. 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! B. higher. © 2013 Pearson Education, Inc.

Absorption of Radiant Energy A material's ability to absorb and radiate thermal energy is indicated by its color. Good absorbers and good emitters are dark in color. Poor absorbers and poor emitters are reflective or light in color. © 2013 Pearson Education, Inc.

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. © 2013 Pearson Education, Inc.

Absorption of Radiant Energy Whether a surface is a net absorber or a net emitter depends on whether its temperature is above or below that of its surroundings. A surface hotter than its surroundings is a net emitter and will cool. A surface colder than its surroundings is a net absorber and will warm. © 2013 Pearson Education, Inc.

Absorption of Radiant Energy CHECK YOUR NEIGHBOR Which melts faster in sunshine: dirty snow or clean snow? Dirty snow Clean snow Both of the above None of the above Explain your answer to your neighbor. A. Dirty snow. © 2013 Pearson Education, Inc.

Absorption of Radiant Energy CHECK YOUR ANSWER Which melts faster in sunshine: dirty snow or clean snow? Dirty snow Clean snow Both of the above None of the above Explanation: Dirty snow absorbs more sunlight, whereas clean snow reflects more. A. Dirty snow. © 2013 Pearson Education, Inc.