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Hewitt/Lyons/Suchocki/Yeh Conceptual Integrated Science. Chapter 6 HEAT. 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
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Hewitt/Lyons/Suchocki/YehConceptual Integrated Science Chapter 6 HEAT
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
6.1 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. Types of motion of particles in matter.
6.2 Temperature 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. Can we trust our sense of hot and cold? Will both fingers feel the same temperature when they are put in the warm water? Try this and feel it for yourself!
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.
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.
Temperature Three different temperature scales differ in zero point and divisions: • Celsius scale freezing point of water: 0C boiling point of water: 100C division: 100 degree units • 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
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 will be the same for both? A. Temperature. • Thermal energy. • Both of the above. • None of the above.
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 will be the same for both? A. Temperature. • Thermal energy. • Both of the above. • None of the above. Explanation: Average kinetic energy of molecules is the same, which means temperature is the same for both.
6.3 Absolute Zero Absolute zero or zero K is the lowest limit of temperature at –273C where molecules have lost all available kinetic energy. A substance cannot get any colder.
6.4 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.
The temperature of the sparks is very high, about 2000°C. That’s a lot of thermal energy per molecule of spark. However, because there are few molecules per spark, internal energy is safely small. Temperature is one thing; transfer of energy is another.
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 A. warm water to the red hot thumbtack. • red hot thumbtack to the warm water. • no heat flow. • not enough information.
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 A. warm water to the red hot thumbtack. • red hot thumbtack to the warm water. • no heat flow. • not enough information.
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°C. 4.18 joules = 1 calorie so 4.18 joules of heat will change the temperature of 1 gram of water by 1°C Although the same quantity of heat is added to both containers, the temperature increases more in the container with the smaller amount of liquid. If you add 1 calorie of heat to 1 gram of water, you’ll raise its temperature by 1°C.
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°C. To the weight watcher, the peanut contains 10 Calories, to the physicist, it releases 10,000 calories (or 41,840 joules) of energy when burned or digested.
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 A. decreases more. • increases more. • does not change. • not enough information.
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 A. decreases more. • increases more. • does not change. • not enough information.
6.5 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. When Pete pushes down on the piston, he does work on the air inside. What happens to the air’s temperature?
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 A. increases. • decreases. • remains unchanged. • is no longer evident.
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 A. 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.
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.
The Laws of Thermodynamics Third Law of Thermodynamics: No system can reach absolute zero.
Entropy 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.
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. • Work is needed to transform a state of disorderly, diffuse energy to a state of more concentrated energy. The Sun supplies the energy to do this work when plants transform liquids and vapors into sugar molecules– a plants storehouse of usable, concentrated energy.
Entropy CHECK YOUR NEIGHBOR Your room gets messier each week. In this case, the entropy of your room is A. increasing. • decreasing. • hanging steady. • nonexistent.
Entropy CHECK YOUR ANSWER Your room gets messier each week. In this case, the entropy of your room is A. increasing. • decreasing. • hanging steady. • nonexistent. Comment: If your room became more organized each week, then entropy would decrease in proportion to the effort expended.
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°C. • thermal inertia that indicates the resistance of a substance to a change in temperature. • sometimes called specific heat. The filling of a hot apple pie may be too hot to eat, even though the crust is not. The crust cools quickly because it has a lower heat capacity!
Specific Heat CHECK YOUR NEIGHBOR Which has the higher specific heat, water or land? A. Water. • Land. • Both of the above are the same. • None of the above.
Specific Heat CHECK YOUR ANSWER Which has the higher specific heat, water or land? A. 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 is a major influence on climate.
6.7 Thermal Expansion 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. The gap in the roadway of a bridge is called an expansion joint. It allows the bridge to expand and contract. (Was this photo taken on a warm day or a cold day?) Thermal expansion accounts for the creaky noises often heard in the attics of old houses on cold nights. The construction materials expand during the day and contract at night, creaking as they grow and shrink.
Thermal Expansion CHECK YOUR NEIGHBOR When stringing telephone lines between poles in the summer, it is advisable to allow the lines to A. sag. • be taut. • be close to the ground. • allow ample space for birds.
Thermal Expansion CHECK YOUR ANSWER When stringing telephone lines between poles in the summer, it is advisable to allow the lines to A. sag. • be taut. • be close to the ground. • 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.
Expansion of Water 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. Liquid water is more dense than ice because water molecules in a liquid are closer together than water molecules frozen in ice, where they have an open crystalline structure.
Close to 0°C, liquid water contains crystals of ice. The open structure of these crystals increases the volume of the water slightly. The six-sided structure of a snowflake is a result of the six-sided ice crystals that make it up.
Expansion of Water Water between 0C and 4C does not expand with temperature. As the temperature of 0 water rises, it contracts until it reaches 4C. Thereafter, it expands. Water is at its smallest volume and greatest density at 4C. When 0C water freezes to become ice, however, it has its largest volume and lowest density.
Expansion of Water Volume changes for a 1-gram sample of water. Between 0°C and 4°C, the volume of liquid water decreases as temperature increases. Above 4°C, water behaves the way other substances do. Its volume increases as its temperature increases. The volumes shown here are for a 1-gram sample.
As water cools, it sinks until the entire lake is 4°C. Then as water at the surface is cooled further, it floats on top and can freeze. Once ice is formed, temperatures lower than 4°C can extend down into the lake.
Expansion of Water CHECK YOUR NEIGHBOR When a sample of 0C water is heated, it first A. expands. • contracts. • remains unchanged. • not enough information.
Expansion of Water CHECK YOUR ANSWER When a sample of 0C water is heated, it first A. expands. • contracts. • remains unchanged. • not enough information. Explanation: Water continues to contract until it reaches a temperature of 4C. With further increase in temperature beyond 4C, water then expands.
Expansion of Water CHECK YOUR NEIGHBOR When a sample of 4C water is cooled, it A. expands. • contracts. • remains unchanged. • not enough information.
Expansion of Water CHECK YOUR ANSWER When a sample of 4C water is cooled, it A. expands. • contracts. • remains unchanged. • not enough information. Explanation: Parts of the water will crystallize and occupy more space.
6.8 Heat Transfer Processes of thermal energy transfer: • conduction • convection • radiation
Heat Transfer: conduction • Conduction: Heat is transferred between substances that are touching • Heat transfer is always from warmer to colder substances • The rate of heat transfer increases as the temperature difference increases • The rate of heat transfer varies with the type of substance • Metal? • Air? • Winter coats • insulation The transfer of heat from the hot end of the metal pin to the cool end by molecular contact is called conduction
Heat Transfer: Conduction Conduction occurs predominately in solids where the molecules remain in relatively restricted locations. The tile floor feels colder than the wooden floor, even though both floor materials are at the same temperature. This is because tile is a better conductro of heat than wood, and so heat is more readily conducted out of the foot touching the tile. When you touch a nail stuck in ice, does cold flow from the ice to your hand, or does energy flow from your hand to the ice?
