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Chapter 16 Thermal Energy and Heat

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Presentation on theme: "Chapter 16 Thermal Energy and Heat"— Presentation transcript:

1 Chapter 16 Thermal Energy and Heat

2 Work and Heat In what direction does heat flow spontaneously? Heat is ________________________________ ____________________________________________________________________________ Heat flows spontaneously from _______objects to ________objects.

3 Temperature What is the temperature of an object related to? Temperature is related to the average kinetic energy of the particles in an object due to their _____________________________________.

4 Temperature Temperature is a _____________________ ____________________________________. On the Celsius scale, the reference points are the ________and __________points of water. On the Kelvin scale, ________________is defined as a temperature of 0 kelvins.

5 Temperature As an object heats up, __________________ ______________________, on average. The average kinetic energy of the particles increases. One way that heat flows is by the transfer of energy in _______________. On average, ________________ particles lose energy. ________________particles gain energy. Overall, collisions transfer thermal energy from _________________________________.

6 Thermal Energy What two variables is thermal energy related to? Thermal energy is the total ____________and ________________energy of all the particles in an object. Thermal energy depends on the __________, ______________, and ______________(solid, liquid, or gas) of an object.

7 Thermal Energy Thermal energy depends on ___________. A cup of tea and a teapot full of tea can have the same temperature. The average kinetic energy of the particles is the same in the cup and the pot. There is more ___________________in the teapot because it contains more particles.

8 Thermal Energy Thermal energy depends on ______________. Compare a cup of hot tea with a cup of cold tea. In both cups, the tea has the same mass and number of particles. The average kinetic energy of particles is higher in the hot tea, so it has __________thermal energy.

9 Thermal Energy Thermal energy depends on mass and temperature. The tea is at a higher temperature than the lemonade. The lemonade has more thermal energy because it has many more particles.

10 Thermal Contraction and Expansion
What causes thermal expansion? Thermal expansion _____________________ ____________________________________________________________________________ Thermal expansion occurs when particles of matter move farther apart as _____________ increases.

11 Thermal Energy If you take a balloon outside on a cold winter day, it _______________in a process of thermal contraction. As temperature ______________, the particles that make up the air inside the balloon move more slowly, on average. Slower particles collide less often and exert less force. Gas pressure _______________and the balloon ______________________.

12 Thermal Energy If you bring the balloon inside, it ________________. Gases expand ________than liquids and liquids usually expand ___________than solids. As temperature increases, the alcohol in a thermometer _______________, and its height increases in proportion to the increase in temperature. In an oven thermometer, strips of steel and brass expand at different rates as the coil heats up. The ___________________________________________________________________________________.

13 Specific Heat How is a change in temperature related to specific heat? Specific heat is _________________________ ____________________________________________________________________________ The lower a material’s specific heat, the more its ______________________________ ____________________________________________________________________________

14 Specific Heat When a car is heated by the sun, the temperature of the metal door increases more than the temperature of the plastic bumper. The iron in the door has a _____________ _____________than the plastic in the bumper.

15 Specific Heat

16 Specific Heat In this formula, heat is in _________, mass is in __________, specific heat is in ________, and the temperature change is in degrees ___________________.

17 Specific Heat 1. How much heat is needed to raise the temperature of g of water by 85.0°C? 2. How much heat is absorbed by a 750-g iron skillet when its temperature rises from 25°C to 125°C? Answer: Q = m * c * ∆T Answer: Q = m * c * ∆T

18 Specific Heat 3. In setting up an aquarium, the heater transfers 1200 kJ of heat to 75,000 g of water. What is the increase in the water’s temperature? (Hint: Rearrange the specific heat formula to solve for ∆T.) Answer: ∆T = Q / (m x c) 4. To release a diamond from its setting, a jeweler heats a 10.0-g silver ring by adding 23.5 J of heat. How much does the temperature of the silver increase? Answer: ∆T = Q / (m x c)

19 Specific Heat 5. What mass of water will change its temperature by 3.0°C when 525 J of heat is added to it? Answer: m = Q / (∆T x c)

20 Specific Heat On what principle does a calorimeter operate? A calorimeter is an ______________________ ______________________________________ The lower a material’s specific heat, the more its temperature rises when a given amount of energy is absorbed by a given mass.

21 Specific Heat According to the law of conservation of energy, ____________________________________________________________________________________________________________________________________________________ The calorimeter is sealed to prevent thermal energy from escaping.

22 Specific Heat A calorimeter is used to measure specific heat. A sample is heated and placed in the calorimeter. _______________________________________________________________

23 What is the thermal energy of an object?
Assessment Questions What is the thermal energy of an object? the total number of atoms or molecules the total kinetic energy of the atoms or molecules the average kinetic energy of the atoms or molecules the average mechanical energy of the atoms or molecules

24 Assessment Questions What causes a gas to expand when its temperature is increased? The number of particles increases as temperature increases. Each particle expands as its temperature increases, so the total volume increases. As temperature increases, more electrons leave atoms and move separately. As gas particles move faster, they overcome some forces of attraction. The specific heat of water is 4.18 J/g•°C. How much heat is required to raise the temperature of 1,000 grams of water by 50°C? 83.6 J 83.6 kJ 209 J 209 kJ

25 What property of matter can be measured using a calorimeter?
Assessment Questions What property of matter can be measured using a calorimeter? temperature thermal expansion specific heat mass Temperature is the transfer of thermal energy from one object to another. True False

26 Newton’s cradle helps to visualize conduction
Newton’s cradle helps to visualize conduction. One ball strikes the rest, and most of the kinetic energy is transferred to one ball on the end.

27 Conduction Why is conduction slower in gases than in liquids or solids? Conduction is __________________________ ______________________________________ Conduction in gases is slower than in liquids and solids because _______________ ____________________________________________________________________________

28 Conduction Conduction occurs within a material or ___________________________________. In conduction, collisions between particles transfer thermal energy, without any overall transfer of matter. A thermal conductor _________________ ______________________________________________________________________

29 Conduction The arrows show how thermal energy is conducted away from the heat source in a metal frying pan.

30 Conduction ____________are good thermal conductors. When a frying pan is on a hot stove, the bottom of the metal pan heats first and the metal handle last. The flames ____________ ____________________________________ Tile is a better conductor than wood. A tile floor feels colder than a wooden floor when both floors are at room temperature. The tile ____________________________________ ________________________________________________________________________

31 Conduction Thermal Insulators A material that conducts thermal energy poorly is called a _____________________. Air is a very good insulator. Wool garments and plastic foam cups use trapped air to slow down conduction.

32 Convection In what natural cycles do convection currents occur? Convection ____________________________ ____________________________________________________________________________ Convection currents are important in many natural cycles, such as _________________, _________________, and movements of ___ _____________________________________.

33 Convection Passing sandbags along a line is like transferring thermal energy by convection. The arrows show convection of air in an oven.

34 Convection A ______________________occurs when a fluid circulates in a loop as it alternately heats up and cools down. Air at the bottom of an oven heats up, expands, and becomes less dense. __________________________. Rising hot air cools as it moves away from the heat source. As a result, the coolest air is at the top of the oven.

35 Radiation How does an object’s temperature affect radiation? Radiation is ___________________________ ____________________________________________________________________________ All objects radiate energy. As an object’s temperature ____________, the rate at which it radiates energy ___________________.

36 Radiation When you stand to the side of a charcoal grill, heat reaches you ______________________ ____________________________________ The sun warms you by ______________on a clear day. The space between the sun and Earth has no air to transfer thermal energy. Heat lamps used in restaurants are another example of radiation.

37 Radiation The heating coil on a stove radiates thermal energy. The changing color of the red arrows indicates that the farther you are from the coil, ______________ ____________________.

38 Thermodynamics _____________________________________________________________________________________________thermodynamics. _____________________( ) carefully measured the energy changes in a system. Joule's system included a falling weight that turned a paddle wheel in a container of water. Joule found that the work done by the falling weight almost exactly equaled the thermal energy gained by the water.

39 Thermodynamics First Law of Thermodynamics The first law of thermodynamics states that _____________________________________.

40 Thermodynamics Energy cannot be created or destroyed, but it can be ______________into different forms. Added energy increases the thermal energy of a system or does work on the system. In either case, energy is conserved.

41 Thermodynamics Pushing on the pump does work on the system. Some of the work is converted into ___________ ________________, which heats the air in the pump and the tire.

42 Thermodynamics Second Law of Thermodynamics The second law of thermodynamics states _____________________________________ _________________________________________________________________________________________________________________.

43 Thermodynamics Thermal energy flows spontaneously only from _____________to ___________________objects. A refrigerator must do work to transfer thermal energy from the cold food compartment to the warm room air. The thermal energy is released by _____________at the bottom or in the back of the refrigerator.

44 Thermodynamics A heat engine is _____________________________ ___________________________________________ The efficiency of a heat engine is always less than _________________ Thermal energy that is not converted into work is called __________________________ Waste heat is lost to the surrounding environment.

45 Thermodynamics __________________________will always make a system less orderly, unless work is done on the system. For example, if you walk long enough, your shoelaces will become untied. But the opposite won't happen; shoelaces don't tie themselves. Disorder in the universe as a whole is always increasing.

46 Thermodynamics Third Law of Thermodynamics The third law of thermodynamics states that _____________________________________.

47 Thermodynamics The efficiency of a heat engine increases with a greater difference between ____________________ ____________________________________________________________________________________ A heat engine could be ________________efficient if the cold outside environment were at absolute zero (0 Kelvin). This would violate the third law of thermodynamics.

48 Thermodynamics The third law of thermodynamics states that absolute zero cannot be reached. This physicist uses a laser to cool rubidium atoms to 3 billionths of a Kelvin above absolute zero.

49 Assessment Questions What form of energy transfer requires the motion of particles of a fluid? conduction convection radiation insulation What happens in every case in which energy is added to a system? Temperature increases. Work is done on the system. All of the energy can be accounted for as work or heat. An identical amount of energy is removed from the system.

50 Assessment Questions Thermal energy can move from a cooler object to a warmer object when the warmer object is larger. the cooler object has more thermal energy. energy is transferred by radiation. work is done on the system. According to the third law of thermodynamics, it is impossible to cool an object to absolute zero. transfer thermal energy from a cooler object to a warmer object. convert energy from one form to another. account for all of the energy in a system.

51 Assessment Questions All metals are good thermal insulators. True False

52 Heat engines played a key role in the development of the modern industrial world. Steam locomotives were an important early use of the steam engine. Electric power plants today use steam turbines.

53 Heat Engines What are the two main types of heat engines? The two main types of heat engines are the ____________________________and the _____________________________________.

54 External Combustion Engine
Heat Engines External Combustion Engine A steam engine is an external combustion engine—an ______________________________ ________________________________________ __________________________developed the first practical steam engine in 1712 to pump water out of coal mines. __________________________designed an engine in 1765 that operated at a higher temperature and was more efficient.

55 Heat Engines When the valve in a steam engine slides, steam is trapped in the cylinder. The steam expands and cools as it pushes the piston to the left. Hot steam in Slide valve Exhaust steam out Valve rod Piston rod Cylinder Piston

56 Heat Engines Internal Combustion Engine An internal combustion engine _____________ ________________________________________________________________________________ Most internal combustion engines use pistons that move up and down inside cylinders. Each upward or downward motion of a piston is called a __________.

57 Heat Engines Most cars have a ________________internal combustion engine. This diagram shows only one of the cylinders during each stroke. Intake valve Spark plug Exhaust valve Air-fuel mixture Cylinder Exhaust gases Piston Intake stroke Compression Stroke Power stroke Exhaust stroke

58 Heat Engines In an internal combustion engine, the cooling system and exhaust transfer heat from the engine to the environment. Gasoline engines are more efficient than old-fashioned steam engines, but they still are not very efficient. About _______________of the energy in a gasoline engine is converted to work.

59 Heating Systems How do most heating systems distribute thermal energy? __________________________________________________________________________________________________________________

60 Heating Systems A central heating system heats many rooms from _________________________________. The most commonly used energy sources for central heating systems are _____________________________ _____________________________________________ Heating systems differ in how they transfer thermal energy to the rest of the building.

61 Heating Systems Hot-Water Heating At the boiler, heating oil or natural gas burns and _________________________________. The circulating pump carries the hot water to ______________________in each room. The hot water transfers thermal energy to the radiator by __________________________.

62 Heating Systems The hot pipes heat the room air by _____________ and _______________________. Hot air rises and sets up a convection current in each room. The cooled water returns to the boiler.

63 Heating Systems Thermostat Within the pipes of this hot-water heating system, the water circulates in a ________________current. In each room, the air moves in a convection current. Radiator Exhaust vent Expansion tank Boiler Circulating pump

64 Heating Systems Steam Heating
Steam heating is very similar to hot-water heating except that ______________ is used instead of hot water. The transfer of heat from the steam-heated radiator to the room still occurs by _____________________. Steam heating often is used in older buildings or when many buildings are heated from one central location.

65 Electric Baseboard Heating
Heating Systems Electric Baseboard Heating An electric baseboard heater ________________ _______________________________________. A conductor is used to convert electrical energy to ___________________________. The hot coil heats the air near it by conduction and radiation. Convection circulates the warm air to heat the room.

66 Heating Systems Forced-Air Heating
Forced-air heating systems use ______________ _______________________________________________________________________________. Convection circulates air in each room. Warm air entering the room ____________________ __________________________________________. Cool room air returns to the furnace through floor vents on the other side of the room.

67 Heating Systems Hot air enters the room through a supply vent in the floor. The hot air rises as cooler, denser air in the room sinks. Hot air rises Cool air sinks Supply vent Return vent Chimney Duct Furnace

68 Cooling Systems How does a heat pump reverse the normal flow of heat? A heat pump __________________________ _____________________________________. Heat pumps must do work on a refrigerant in order to reverse the normal flow of thermal energy.

69 Cooling Systems A refrigerant is a ____________________________ __________________________________________ When the refrigerant absorbs heat, ________________ _____________________________________________ When the refrigerant gives off heat,_________________ _____________________________________________

70 Cooling Systems Refrigerators
A refrigerator is a heat pump—_______________ _______________________________________________________________________________. A ______________must do work to move refrigerant through tubing inside the refrigerator walls. Coils of tubing underneath or behind the refrigerator release heat absorbed from the food compartment and thermal energy produced by the work the motor does.

71 Cooling Systems When a refrigerator door is open, some thermal energy from the room enters the refrigerator. _______ ___________________________________________________. Temperature in room: 25°C Temperature in refrigerator: 3°C

72 Cooling Systems Air Conditioners The ________________ in a room air conditioner raises the temperature and pressure of the refrigerant, turning it into a hot, high-pressure gas. The condenser coil is hotter than the outside air, so heat flows spontaneously to the outside air. The ________________cools and condenses into a liquid.

73 Cooling Systems The liquid refrigerant then flows through the expansion valve and ________________________. As the cold refrigerant flows through the evaporator coil, it absorbs _________________ from the warm room air. The fan sends cold air back into the room. The refrigerant becomes a vapor, and the process starts all over again.

74 Cooling Systems In a window air conditioner, outside air is heated as a fan blows it through the condenser coil. Condenser coil Vapor cools to liquid as heat is removed. Warm air out Cold air out Compressor Expansion valve Pressure drops, causing liquid refrigerant to become cold. Warm air in Evaporator coil Liquid absorbs heat to become vapor.

75 Assessment Questions Only about one-third of the energy in gasoline is converted to work in an internal combustion engine. The rest of the chemical energy is lost as unused mechanical energy. destroyed by the engine. converted to potential energy. discharged as waste heat. How is a room heated by an electric baseboard heating system? conduction and convection only conduction and radiation only convection and radiation only conduction, convection, and radiation

76 Assessment Questions How do air conditioners reverse the normal flow of heat? moving cool air from outside to inside the house separating warm atoms from cool atoms vaporizing and condensing a refrigerant blowing the warm air away with a fan Forced air heating systems are often used to heat many buildings from a central location. True False

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