Thermal Energy and Heat

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Thermal Energy and Heat

• Chapter 14

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Section 1 Temperature, Thermal Energy, and Heat
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Temperature

• A measure of the average kinetic energy of the
  individual particles in matter.
• The faster the particles move, the more kinetic
  energy.
• We use a thermometer to measure temperature.
• 3 Scales Celsius, Fahrenheit, Kelvin

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• Celsius scale
• Boiling point of water 100C
• Freezing point of water 0C
• Fahrenheit scale
• Boiling point of water 212F
• Freezing point of water 32F
• Kelvin scale
• Boiling point of water 373K
• Freezing point of water 273K

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• C K - 273
• K C 273 formulas
• Convert 303K to C
• 303K 273 30C
• Convert 70C to K70C 273 343K
• absolute zero 0K or -273 C
• At absolute zero, there is no kinetic energy in
  the particles / no thermal energy can be removed

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Thermal Energy and Heat

• Thermal Energy depends upon
• 1. the number of particles in the object
• 2. the temperature of the object
• 3. the arrangement of the particles
• Heat is
• thermal energy which moves from a warmer object
  to a less warm object.
• Example-ice cube melting in your hand

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Examine the beakers below.

• Which beaker holds more water molecules?
• Which beaker has a higher temperature?
• Which beaker has more kinetic energy?
• Which beaker has more thermal energy?
• Which beaker has the greatest mass?

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Specific Heat

• The amount of energy required to raise the
  temperature of one kilogram of a material by one
  Kelvin.
• Unit for specific heat J/(kgK)Formula
• change in energy mass x specific heat x change
  in temperature
• Material with a high specific heat can absorb a
  lot of thermal energy without a great change in
  temperature.

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• Materials with a low specific heat will absorb
  heat quickly and easily.
• Ex Sand on the beach
• Ex gold (bracelet)
• Ex concrete/pavement/tar
• Ex iron
• Ex copper
• Ex silver

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Sample Problem

• How much heat energy is required to raise the
  temperature of 5kg of water by 10 Kelvins?
• Given information
• mass 5kg
• change in temp (?T) 10K
• specific heat of water 4180J/(kgK)
• Unknown change in energy

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3 Steps to Solve This Problem
Formula change in energy mass x specific heat x ?T
Substitution energy 5kg x 4180J/(kgK) x 10K
Answer 20,900 J
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Section 2The Transfer of Heat
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How is Heat Transferred?

• 3 ways that heat can move
• 1. Conduction
• 2. Convection
• 3. Radiation

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Conduction

• Heat is transferred by the direct contact of
  particles
• Example the heat energy from the hot soup is
  transferred by conduction to the spoonthe spoon
  then becomes warm.

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Convection

• Heat is transferred by the movement of currents
  within a fluid (liquid or a gas)
• Example boiling waterwater is moved by the
  currents in the fluid
• When fluids are heated, the particles move faster
  and further apart.
• Pizza oven
• Opening an oven and feeling a blast of hot air

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• When fluids are heated, they rise upward because
  they become less dense
• Example hot water/air rises and cool water/air
  sinks
• The rise and fall of these fluids create
  convection currents (circular motion)

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Radiation

• The transfer of heat energy by electromagnetic
  waves
• Example fire, suns energy
• Does not require matter to transfer thermal energy

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Heat Moves One Way

• Heat will always flow from a warmer object to a
  cooler object.
• As thermal energy increases, the temperature of
  matter absorbing the heat increases.
• The temperature of the matter losing the thermal
  energy is dropping.
• Note there is no such thing as coldness

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Conductors and Insulators

• Conductor material that transfers thermal
  energy well
• metal spoon
• most metals
• Insulator material that does not transfer
  thermal energy well
• wood
• wool
• straw
• goose feathers/down comforter
• insulation

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Section 3 Thermal Energy and States of Matter
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• States of Matter
• Solid
• Particles are packed tightly together
• Particles only vibrate
• Retain their shape and volume

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• Liquid
• particles are close together
• particles are free to move around
• does not have a definite shape
• has a definite volume

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• Gas
• particles are moving very fast!
• particles are spread very far apart
• gases expand to fill available space
• lack a fixed shape and volume

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Changes of State

• Change of State physical change of matter from
  one state of matter to another (occurs when heat
  energy is absorbed or released)
• Solid-Liquid Changes
• 1. melting solid changes to a liquid
• 2. freezing liquid changes to a solid

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• Liquid-Gas Changes
• Vaporization change from a liquid to a gas
  (absorbs heat energy)
• 1. evaporation vaporization that takes place
  at the surface of a liquid
• 2. boiling vaporization that takes place below
  the surface of a liquid
• 3. condensation a change from a gas to a
  liquid (cold drink in the summer-loses heat
  energy)

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Thermal Expansion

• As the thermal energy of matter increases, its
  particles spread out and the substance expands.
• The expansion of matter when it is heated is
  thermal expansion.
• Example metal grooves on a bridge