1. Chapter 14: Thermal Energy & Heat
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2. Introduction
Heat is the transfer of thermal energy.
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3. Topics of Discussion Temperature , Thermal Energy, and Heat (Section1)
The Transfer of Heat (Section 2)
Thermal Energy and States of Matter (section 3)
Uses of Heat (Section 4)
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4. TEMPERATURE and THERMAL ENERGY (Section one)
Temperature is the measure of the average kinetic energy of the individual particles in matter.
Three common Temperature scales for measuring temperature
Fahrenheit
Celcius
Kelvin
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5. Fahrenheit (Section one)
U.S. System
Water Freezes at 32o
Water Boils at 212o
180 equal intervals between freezing and boiling called degrees Fahrenheit (oF)
Absolute zero is -460o
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6. Absolute Zero (Section one)
Absolute zero is the lowest temperature possible.
At this temperature, no more energy can be removed from matter.
-460oF
-273oC
0 K
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7. Celcius Scale (Section one)
This system is used in most of the world.
Water Freezes at 0o
Water Boils at 100o
100 equal intervals between freezing and boiling called degrees Celcius (oC)
Absolute zero is -273o
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8. Kelvin Scale (Section one)
This system is used most in physical science.
Units on the Kelvin scale are the same size as those in Celcius – called kelvins (K)
Water Freezes at 273o
Water Boils at 373o
Absolute zero is 0o
The Kelvin scale is defined so that zero is absolute zero.
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9. Thermal Energy (Section one)
Thermal energy is the total energy of all of the particles.
Heat is thermal energy moving from a warmer object to a cooler object. (Only = One way.)
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10. Thermal Energy (Section one)
Specific Heat – The amount of energy required to raise the temperature of one kilogram of a substance by 1 kelvin.
Δ energy = Mass X Specific heat X Δ temperature (Δ = change)
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11. Thermal Energy (Section one)
Units = Joules per kilogram-Kelvin
J/(kg·K)
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12. The Transfer of Heat (Section 2)
Heat is transferred by:
Conduction,
Convection, and
Radiation.
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13. Conduction (Section 2)
Heat is transferred from one particle of matter to another without the movement of matter itself.
Ex: A metal spoon in a pot of water on an electric stove. The fast moving (hot) particles of the element collide with the slow (cold) particles of the pot and energy is transferred.
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14. Convection (Section 2)
Heat is transferred by the movement of currents within a fluid (liquid or gas.)
Ex: Water heating in a pot on the stove.
Differing densities cause the water to flow in a circular motion known as a convection current.
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15. Radiation (Section 2)
The transfer of energy by electromagnetic radiation.
Radiation does not require matter to transfer thermal energy.
Ex: Heat from a fireplace, the sun, heat lamp, and a microwave oven.
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16. Heat Moves One Way (Section 2)
If two objects have different temperatures , heat will flow from the warmer object to the colder one.
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17. Conductors and Insulators (Section 2)
Conductor – A material that conducts (transfers) heat well.
Ex: metal.
Insulator – A material that does not conduct heat well.
Ex: Wood, Glass and gasses.
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18. Thermal Energy and States of Matter (Section 3)
Most matter on Earth can exist in three states:
Solids
Liquids
Gases
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19. Solids (Section 3) Ex: Ice cube & text book Tightly packed particles
Particles in fixed position (vibrate)
Definite volume & shape
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20. Liquids (Section 3) Ex: Water & Molten steel
Particles close together (further than solid)
Particles can move around
Definite volume, random shape
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21. Gases (Section 3) Ex: Steam & air Fast moving / far apart particles
Particles free to move
Random volume, random shape (Expand to fit space available)
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22. Changes of State (Section 3)
Change of state is the physical change from one state of matter to another.
Matter will change from one state to another if thermal energy is absorbed or released.
Solid-Liquid
Liquid-Gas
(Temperature = constant)
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23. Solid – Liquid Changes of State (Section 3)
Melting
From solid to liquid
A solid absorbs thermal energy
Melting point = temperature at which a solid changes to liquid
Freezing
From liquid to solid
Matter releases thermal energy
Freezing point = temperature at which a liquid changes to solid
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24. Liquid - Gas Changes of State (Section 3)
Vaporization
From liquid to gas
Liquid absorbs thermal energy
Evaporation = vaporization on surface
Boiling = vaporization within liquid
Boiling point = temperature at which a liquid changes to gas
Condensation
From gas to liquid
Thermal energy decreases
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25. Thermal Expansion (Section 3)
As thermal energy of a substance increases, its particles spread out and the substance expands.
Thermometers
Expanding liquid – Mercury or alcohol
Thermostats
Expanding bimetallic strips
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26. Uses of Heat (Section 4) Heat Engines – External Combustion Engines
Transform thermal energy to mechanical energy
External Combustion Engines
Fuel is burned outside the engine
howstuffworks.com/steamengine
Internal Combustion Engines
Fuel is burned in cylinders inside the engine.
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27. Internal Combustion Engines (Section 4)
Gasoline and Diesel
Pistons move up and down (one stroke) to drive crankshaft
Two Stroke
Four- Stroke
Intake Stroke
Compression Stroke
Ignition
Power Stroke, and
Exhaust Stroke
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28. Refrigerators (Section 4)
A refrigerator is a device that uses an outside energy source to transfer thermal energy from a cool area to a warm area.
Refrigerant – The substance that absorbs and releases heat in a refrigerator
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29. Key Terms Absolute Zero Heat Conduction Convection Convection Current
Radiation
Insulator/Conductor
Specific Heat
State
Change of State
Melting (point)
Freezing (point)
Boiling (point)
Condensation
Thermal Expansion
Heat Engine
Internal Combustion
External Combustion
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