Thermal Energy
Thermal Energy
• Temperature & Heat
• Temperature is related to the
average kinetic energy of the
particles in a substance.
• SI unit for temp. is the Kelvin
• K = °C + 273 (10°C = 283K)
• °C = K – 273 (10K = -263°C)
• Thermal Energy –
the total of all the
kinetic and
potential energy
of all the particles
in a substance.
• Thermal energy relationships
• As temperature increases, so
does thermal energy (because
the kinetic energy of the
particles increased).
• Even if the temperature doesn’t
change, the thermal energy in a
more massive substance is higher
(because it is a total measure of
energy).
Heat
Cup gets cooler while
hand gets warmer
•The flow of
thermal energy
from one object to
another.
• Heat always
flows from
warmer to
cooler objects.
Ice gets warmer
while hand gets
cooler
Types of Heat Transfer
3 WAYS THAT HEAT CAN
TRAVEL SONG:
• https://www.youtube.com/watch?v=7Y3mf
AGVn1c
Types of Heat Transfer
Conduction
Conduction is the
transfer of heat
by direct contact.
*occurs best in
solids
Types of Heat Transfer
Convection
• Convection is the transfer of heat through
fluids by currents created due to density
differences in parts of the fluid. *occurs in
liquids and gases only
Hot water rises, cools and
falls.
Heated air rises, cools
and then falls.
Cool air falls.
Types of Heat Transfer
Radiation
• Radiation is the transfer of heat energy through
space as waves of electromagnetic radiation. *the
only type that can occur through empty space
(example: from the sun)
Specific Heat
• Some things heat up or cool
down faster than others.
Land heats up and cools down faster than
water.
Specific heat is the amount of
heat required to raise the
temperature of 1 kg of a material
by one degree (C or K).
C water = 4184 J / kg C
C sand = 664 J / kg C
This is why land heats up quickly
during the day and cools quickly at
night and why water takes longer.
Specific Heat
• Which take longer
to heat to 100°C?
50g Al 50g Cu
C
Water
Aluminum
Copper
Silver
Gold
C
(cal/g°C)
(J/g°C)
1.00
0.22
0.093
0.057
0.031
4.18
0.90
0.39
0.24
0.13
Aluminum has a higher specific heat, so it
will take longer to heat up. It will ALSO
take longer to cool down.
Why does water have such a
high specific heat?
water
metal
Water molecules form strong bonds
with each other; therefore it takes
more heat energy to break them.
Metals have weak bonds and do not
need as much energy to break them.
How to calculate changes
in thermal energy
q = mCpT
q = change in thermal energy (heat)
m = mass of substance
T = change in temperature (Tf – Ti)
Cp = specific heat of substance
-q means heat loss
+q = heat gain
Heat Transfer
A 32g silver spoon cools from 60°C to
20°C. How much heat is lost by the
spoon?
GIVEN
m = 32g
Ti = 60°C
Tf = 20°C
q = ??
C = 0.235 J/g°C
WORK
q = mCΔT
m = 32g
ΔT = Tf - Ti
ΔT = 20°C – 60°C = -40°C
q = (32g)(0.235J/g°C)(-40°C)
q = -300.8 J
Heat Transfer
How much heat is required to warm 230 g of
water from 12°C to 90°C?
GIVEN
m = 230g
Ti = 12°C
Tf = 90°C
Q = ??
C = 4.184 J/g°C
WORK
q = mCΔT
m = 230g
ΔT = Tf - Ti
ΔT = 90°C – 12°C = 78°C
q = (230g)(4.184J/g°C)(78°C)
q = 78,061 J
A piece of iron at a temperature of 145°C cools off
to 45°C. If the iron has a mass of 10 g and a
specific heat of 0.449 J/g°C, how much heat is
given up?
GIVEN
m = 10g
Ti = 145°C
Tf = 45°C
q = ??
C = 0.449 J/g°C
WORK
q = mCΔT
m = 10g
ΔT = Tf - Ti
ΔT = 45°C – 145°C = -100°C
q = (10g)(0.449J/g°C)(-100°C)
q = -449 J
A calorimeter is used to
help measure the
specific heat of a
substance.
Heat gained = Heat lost
First, mass and
Knowing
its
q
value,
temperature of
Thengives
heated
its
mass,
and
its
This
the
water
are
measured
T
is
measured
sample
put
T, its Cp can be heat
lostisby
the
for water
to
help
inside
and heat
calculated
substance
get its heat gain
flows into water
Let’s Practice!
A 55.1 g piece of metal is heated to a temp of 45.1°C,
and placed into a cup containing 359g of water at
20.0°C. The final temp of the water and metal is
22.3°C.
• How much heat energy did the water absorb?
q = mcΔT
q = (359g)(4.18J/g°C)(22.3°C – 20.0°C) = 3.45 x 103J
• How much heat energy did the metal release to the water?
q lost = q gained
q lost by the metal = - 3.45 x 103J
The q is negative because heat was lost.
• What is the specific heat of the metal?
3.45 x 103J = (55.1g)(C)(22.3°C – 45.1°C)
2.75 J/g°C = C
Heat of Fusion
They Quantity of heat absorbed
when a specific quantity of the
solid is converted to liquid at its
melting point is called its heat of
fusion.
Heat of Vaporization
• The quantity of heat absorbed when a
specific quantity of the liquid is
converted to gas at the boiling point is
called the heat of vaporization.
Phase Diagram
Water boils
Ice metls
Fusion
Vaporization