Kinetic Molecular Theory of Heat
•
Atoms held by electromagnetic forces
•
Atoms vibrate
•
Thermal energy is a measure of this
motion.
•
Add heat = increase motion and thermal
energy.
3D Lattice Model
Temperature
•
A measure of average particle kinetic
energy
•
A measure of thermal energy.
•
Not dependent on mass.
Thermometer
•
Measures temperature
•
Place in contact with object
•
Wait for thermal equilibrium
(temperatures are equal)
•
Read the temperature
Thermal equilibrium
•
The energy transfers back and forth
between two objects are equal
•
OR net zero energy transfer
Temperature Scales
Celsius:
freezing point = 0
boiling points = 100.
Kelvin:
absolute zero = 0
•
atoms are motionless.
•
Kelvin = SI unit of temperature.
Compare Scales
Kelvin
Celsius
Fahrenheit
Boiling
373
100
212
Freezing
273
0
32
Absolute
Zero
0

273

459.67
Conversions
•
K = ºC + 273
•
Heat:
energy flows between objects
Due to temp. difference
Always from hot to cold
•
Heat Transfer:
Conduction, Convection,
and Radiation
Conduction
•
Heat transfer when two objects in
contact
Convection
•
Heat transferred by fluid motion
•
Warm air rises
•
Lava Lamp
Radiation
•
Energy transfer by electromagnetic
waves.
•
Sunlight, toaster, campfire
•
Solar collector
Specific Heat
•
C: material property, the amount of
energy required to raise 1 kg by 1 K.
•
Unit = J/kg∙K
•
Examples:
Water C = 4180 J/kg∙K
Iron
C = 450
Copper C = 385
Heat Transferred
•
Amount of heat gained or lost by an
object
Q = mC∆T
•
Q = heat transferred (unit = joules)
•
m = mass
•
C = specific heat
•
∆T = change in temp.
Example
1 kg. of Iron is heated from 37 ºC to
57 ºC. The specific heat of iron is 450
J/kgK. What was the heat transferred
to the iron?
Q
= mC∆T
= (1 kg)(450 J/kgC)(57 ºC
–
37 ºC)
= 1 x 450 x 20
= 9,000 J
Heat Transfer and Temperature
Heat lost by one must equal heat gained by
other
Both end up at same final temperature
hot
object
cold
object
Heat
insulation
•
Q
lost
= Q
gained
•
mC∆T
lost
= mC∆T
gained
•
mC(T
f

T
i
)
hot object
= mC(T
f

T
i
)
cold material
•
Watch your +/

signs
Example
Drop 0.020 kg Iron at 180 ºC into 0.40
kg water at 10 ºC. What’s the final temp?
mC(T
f

T
i
)
iron
+ mC(T
f

T
i
)
water
= 0
(0.02)(450)(Tf
–
180) + (0.4)(4180)(Tf
–
10) = 0
9(Tf

180) + 1672(Tf

10) = 0
9Tf
–
1620 + 1672Tf
–
16720 = 0
1681Tf
–
18340 = 0
1681Tf = 18340
Tf = 18340/1681
Tf = 10.9 ºC
Change of State
•
3 Phases: Solid
–
Liquid

Gas
•
Kinetic Molecular model: atoms joined
by bonds
•
Add heat, increase temp, bonds break

Solid becomes liquid at Melting Point

During melting, no temp. increase
Add more heat
•
temp. increases to boiling point

Liquid becoming vapor

During vaporization, no temp. increase
Melting
Vaporizing
Freezing
Condensing
Temperature
Heat Added
•
Heat of Fusion: energy needed to melt
1 kg of solid.
Q=mH
f
H
f
= heat of fusion
m = mass
•
Heat of Vaporization: energy needed to
vaporize 1 kg of liquid.
Q=mH
v
H
v
= heat of vaporization
m = mass
Thermal Expansion
•
As temp increases, matter expands
•
Increase length
•
Increase volume
•
Water exception
–
expands as it
freezes
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