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Chapter 14: Thermal Energy & Heat

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Introduction

Heat is the transfer of thermal energy.

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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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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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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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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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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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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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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.)

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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Thermal Energy (Section one)

Units = Joules per kilogram-Kelvin J/(kg·K)

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The Transfer of Heat(Section 2)

Heat is transferred by:

1) Conduction,

2) Convection, and

3) Radiation.

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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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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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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.

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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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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Thermal Energy andStates of Matter(Section 3)

Most matter on Earth can exist in three states:

1) Solids

2) Liquids

3) Gases

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Solids (Section 3)

Ex: Ice cube & text book Tightly packed particles Particles in fixed position (vibrate) Definite volume & shape

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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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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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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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Solid – LiquidChanges 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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Liquid - GasChanges 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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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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Uses of Heat(Section 4)

Heat 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.http://auto.howstuffworks.com/4Stroke

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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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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 refrigeratorhttp://home.howstuffworks.com/refrigerator

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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