Thermal Energy
and Heat
Chapter 14
Section 1:
Temperature,
Thermal Energy,
and Heat
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
Celsius scale
Boiling point of water = 100˚C
Freezing point of water = 0˚C
Fahrenheit scale
Boiling point of water = 212˚F
Freezing point of water = 32˚F
Kelvin scale
Boiling point of water = 373K
Freezing point of water = 273K
˚C = K - 273
K = C + 273
formulas
• Convert 303K to ˚C
• 303K – 273 = 30˚C
• Convert 70˚C to K
70˚C + 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
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
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?
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/(kg*K)
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.
• 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
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/(kg*K)
• Unknown: change in energy
3 Steps to Solve This Problem
Formula:
change in energy = mass x specific heat x ∆T
Substitution:
energy = 5kg x 4180J/(kg*K) x 10K
Answer:
20,900 J
Section 2:
The Transfer of Heat
How is Heat Transferred?
• 3 ways that heat can move:
–1. Conduction
–2. Convection
–3. Radiation
Conduction
• Heat is transferred by the direct contact
of particles
• Example: the heat energy from the hot
soup is transferred by conduction to
the spoon—the spoon then becomes
warm.
Convection
• Heat is transferred by the movement of
currents within a fluid (liquid or a gas)
• Example: boiling water—water 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
• 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)
Radiation
• The transfer of heat energy by
electromagnetic waves
• Example: fire, sun’s energy
• Does not require matter to transfer
thermal energy
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”
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
Section 3:
Thermal Energy and
States of Matter
• States of Matter
• Solid
–Particles are packed tightly
together
–Particles only vibrate
–Retain their shape and volume
• Liquid
–particles are close together
–particles are free to move around
–does not have a definite shape
–has a definite volume
• Gas
– particles are moving very fast!
– particles are spread very far apart
– gases expand to fill available space
– lack a fixed shape and volume
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
• 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)
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