Download The Nature of Heat

Thermal Energy
Intro Video
Thermal Energy
• The total energy of particles of a substance or
material.
– As thermal energy increases, particle movement
increases.
– 3 states of matter:
• Solids – thermal energy is low due to little to no
particle movement.
• Liquids – thermal energy is minimal due to slight
particle movement.
• Gases – thermal energy is high due to rapid particle
movement.
As thermal energy increases, particle movement increases.
Thermal Energy Reactions
• When a substance or material gains or loses
thermal energy, two types of reactions are
taking place:
1. Endothermic Reaction – A chemical change that
absorbs heat.
1. Ice melting or water evaporating
2. Exothermic Reaction – A chemical change that
gives off heat.
1. Digesting food, fire burning, or condensation.
Endothermic Reactions
• Energy is absorbed by a substance/material.
– The final temperature of the substance is greater
than the beginning temperature.
• Potential energy < Kinetic Energy (Positive KE)
+KE
Activation
Energy ΔH
PE
Exothermic Reaction
• Energy is released by a substance/material.
– The final temperature of the substance is lower than
the beginning temperature.
• Potential Energy > Kinetic Energy (negative KE)
Activation Energy
PE
ΔH
-KE
Heat
• A form of energy caused by the internal
motion of molecules of matter.
– An increase in temperature = heat is being added.
– A decrease in temperature = heat is being
removed.
• Measured in units called Calories.
– 1 calorie = the amount of heat needed to raise the
temperature of 1g of water 1°C.
• The amount of heat needed for temperature change
depends on the mass of the water being heated.
Specific Heat Capacity
• Mass is not the only factor that determines
temperature change, what the substance is
made of also affects its ability to absorb or
lose heat – specific heat.
– The number of calories needed to raise or lower
the temperature of 1g of a substance 1°C.
• Knowing the specific heat of a substance is useful in
trying to decide what substance should be used for a
specific purpose.
Specific Heats
– What substance heats/cools
the fastest?
Mercury - .03
– What substance heats/cools
the slowest?
Water – 1.0
– To boil water the fastest,
what type of pan would I
want to heat it up in;
aluminum, copper, glass or
iron?
Copper - .09
Substance
Specific Heat
Air
.25
Aluminum
.22
Copper
.09
Glass
.2
Ice
.5
Iron
.11
Mercury
.03
Ocean Water
.93
Water
1.0
Wood
.42
Thermal Expansion
• As a substance gains or loses heat, the surface
of the substance changes – thermal expansion.
– Gains heat = expands
• Molecules gain energy and therefore move more rapidly.
– Increases the substances volume and decreases its density.
– Loses heat = contracts
• Molecules lose energy and therefore move slower.
– Decrease the substances volume and increases its density.
Mechanics of a Hot Air Balloon
• Why does a hot air balloon fly?
• Hot air = increased thermal temp.
• Increased volume
• Decreased density
• Balloon rises.
• What needs to be done to get the balloon to
land?
• Cooler air = decreased thermal temp.
• Decreased volume
• Increased density
• Balloon sinks
Heat Transfer
• Heat moves between objects constantly. But it
always moves from a warmer object to a cooler
object – Heat Transfer.
• 3 Types of Energy Transfer:
1. Conduction
2. Convection
3. Radiation
Conduction
• The transfer of heat from
one substance to another
through direct contact.
– All molecules have motion:
• Faster = more heat energy
• Slower = less heat energy.
– Heat always moves from
the faster moving particle
(hot) to the slower moving
particle (cold).
Slower
Faster
Conductor Vs. Insulator
Any substance that
permits the flow of heat
or electricity freely –
Conductor
Any substance that does not
permit the flow of heat or
electricity freely – Insulator
Example
Insulator
X
Using a metal spoon to stir hot water.
Using a Styrofoam cup to carry hot coffee.
Wearing a feather filled coat in the winter.
Putting a paperclip into an electrical outlet.
Conductor
X
X
X
Convection
• The transfer of heat by the
movement of currents
within a fluid (liquid or gas).
– Hotter fluid = faster moving
particles
• less dense and rises to the
surface.
– Cooler fluid = slower moving
particles
• More dense and sinks to the
bottom.
Convection Currents
• Many of nature’s occurrences happen due to
convection currents.
Wind Currents
Continental Plates Shifting
Ocean Currents
Radiation
• The transfer of heat energy through empty
space by waves = electromagnetic spectrum.
– Does NOT require matter for the energy to be
transferred.
Low
Energy
High
Energy
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