Chapter 10 Section 2
Page 348
Temperature & Kinetic Energy
 The energy of moving objects is Kinetic Energy
 The temperature of a material is a measure of
the average kinetic energy of the particles that
make up the material
Kelvin
Temperature
Average Kinetic Energy
The Kelvin Scale
 Could Kinetic Energy be as low as zero
no particle motion at all ?!?
 As a substance is cooled, it loses more
of its kinetic energy. The temperature
at which a substance would have ZERO
Kinetic Energy is called ABSOLUTE
ZERO.
 No particles would be moving at all.
 The speed & kinetic energy = zero
The Kelvin Scale
 The Kelvin Scale is defined so that the
temperature of a substance is directly
proportional to the average kinetic
energy of the particles
 The zero on the Kelvin scale
corresponds to zero kinetic energy
 Therefore, absolute zero corresponds to
zero on the Kelvin Scale
The Kelvin Scale
 A zero reading on the Celsius or Fahrenheit
scales does NOT correspond to zero kinetic
energy - atoms are still moving at Oo C
(freezing) and Oo F (it’s below freezing, but
atoms are still moving!)
K
oC
oF
_____373_______100_______ 212__________________boiling pt. (water)
_____273_______0__________32__________________freezing pt. (water)
_____0_________-273_______-459_________________Absolute zero
Answer This!
What is the advantage of using the Kelvin scale?
No negative numbers makes
calculations simple
Has Absolute Zero ever been reached?
No, but using a laser-cooling technique that
could one day allow scientists to observe quantum
behavior in large objects, MIT researchers have cooled a
coin-sized object to within one degree of absolute zero.
{ScienceDaily (Apr. 8, 2007) }
Temperature Conversions
 Since the Celsius degree
& the kelvin are the same
size, and Kelvin readings
are 273 degrees higher
than Celsius readings,
simply add 273 to the
Celsius reading to convert
to Kelvin:
Tk = (Tc + 273) K
Temperature Conversions
 Similarly, a Kelvin reading can be expressed as a
celsius reading by subtracting 273:
Tc = (Tk – 273)
oC
Temperature Conversions
Tc = (Tk – 273) oC
Tk = (Tc + 273) K
Complete the following conversions using the
equations above:
Temperature
Celsius
Melting point of iron
Household oven
1808
350
Food freezer
Sublimation point of dry
ice
Boiling point of nitrogen
Kelvin
255
-78.5
77.4
Temperature Conversions
Tc = (Tk – 273) oC
Tk = (Tc + 273) K
Complete the following conversions using the
equations above:
Temperature
Celsius
Kelvin
Melting point of iron
1535
1808
Household oven
350
623
Food freezer
-18
255
Sublimation point of dry
ice
-78.5
194.5
Boiling point of nitrogen
-195.6
77.4
Temperature Conversions
 Because Fahrenheit
degrees are smaller
than Celsius degrees
the conversion
equation is a bit more
complex:
oC=5/9(oF-32)
oF=9/5oC + 32
Temperature Conversions
oC=5/9(oF-32)
To convert from Fahrenheit TO Celsius
1) subtract 32 from the Fahrenheit temp.
2) multiply by 5
3) divide by 9
(Do what is in the parenthesis FIRST)
Convert 120 oF into celsius:
Temperature Conversions
oF=9/5oC + 32
To convert from Celsius TO Fahrenheit
1) multiply by 9
2) divide by 5
3) add 32
(NO parenthesis, so multiply & divide FIRST)
Convert 22oC into Fahrenheit:
Temperature Conversions
oC=5/9(oF-32)
oF=9/5oC + 32
Using the above equations, convert the following:
Temperature
Celsius
A warm day
25
Body temperature
Room temperature
Freezing point of water
Fahrenheit
98.6
20
32
Temperature Conversions
oC=5/9(oF-32)
oF=9/5oC + 32
Using the above equations, convert the following:
Temperature
Celsius
Fahrenheit
A warm day
25
77
Body temperature
37
98.6
Room temperature
20
68
Freezing point of water
0
32
HOMEWORK
Complete the
“Temperature Conversions”
worksheet
for TOMORROW
Mass & Speed of Particles
 The Kinetic Energy of a moving object
depends on both its mass AND its speed
 A bowling ball will have more kinetic
energy & will knock over more pins the
faster it is moving
Mass & Speed of Particles
 A loaded shopping cart will have more
kinetic energy than an empty cart
being pushed at the same speed
 It takes more work and more kinetic
energy to move heavier objects.
Diffusion
 The process by which particles of matter fill
a space because of random motion.
 The rate of diffusion of a gas depends upon
its kinetic energy, that is, on the mass and
speed of its molecules
The faster the speed, the faster the diffusion
 The lighter the molecule, the faster its diffusion

Changing State
 Physical change of matter from solid to
liquid to gas.
 Temperature plays an important role in
changing states.
 There are five processes involved in
changing states: evaporation, sublimation,
condensation, boiling, and freezing
Evaporation
 The process by which particles of a liquid
form a gas by escaping from the surface.
 The area of the surface, as well as the
temperature and humidity, affects the rate
of evaporation
 Which will evaporate faster?
Evaporation
 Liquids that evaporate quickly, like perfume
and paint, are called volatile liquids.
 We spray perfume on our skin to increase
the volatility and scent by increasing the
size of the surface area where evaporation
takes place.
Evaporation
 As liquids evaporate, they cool
 This is the reason we sweat on a hot
day. As the liquid evaporates from our
skin, it cools us down.
Sublimation
 Some solids can change into a gas directly
without melting first.
 This process by which particles of a solid
escape from its surface and form a gas is
called sublimation
Sublimation
 Dry ice (solid CO2)
sublimes.
 Ice can also sublime. Molecules of ice can
leave the surface and become water vapor,
which then freezes. This is the cause of
freezer burn.
 Potpourri molecules sublime
into the air as fragrance.
Condensation
 Condensation is the reverse of evaporation.
 Gas particles come closer together (they
condense) and form a liquid or a solid.
 The term “vapor” is used to describe the
gaseous state of a substance that is liquid at
room temperature
Vapor Pressure and Boiling
 In a closed container, when the particles of
a substance are evaporating and
condensing at equal rates, equilibrium
has been reached.
The pressure exerted by
the vapor in equilibrium
with its liquid is its
vapor pressure.
Vapor Pressure and Boiling
 The value of the vapor pressure of a
substance indicates how easily the
substance evaporates.
 Volatile substances, like alcohols, have
a high vapor pressure, which means
they evaporate easily.
Vapor Pressure and Boiling
 In the same way that kinetic energy and
temperature are related, temperature and
vapor pressure are also related.
 The evaporation rate is higher at higher
temperatures
Vapor Pressure and Boiling
 The boiling point of a liquid is the
temperature when its vapor pressure
equals the pressure exerted on the
surface of the liquid.
 In an open container, the temperature rises
until the vapor pressure equals atmospheric
pressure. Small bubbles of vapor form
below the surface and rise. The liquid boils.
Vapor Pressure and Boiling
 When the pressure being exerted on a
liquid increases, it takes more energy to
raise the vapor pressure of that liquid
to get it to boil. The boiling point
temperature also increases.
 If there is less pressure being exerted
on a liquid, the boiling point
temperature decreases.
Vapor Pressure and Boiling
THINK ABOUT IT!
 Why do foods cooked in boiling water
at higher altitudes need to be cooked
LONGER?
Vapor Pressure and Boiling
THINK ABOUT IT!
 Why do foods cooked in boiling water at
higher altitudes need to be cooked
LONGER?
Because the LOWER
atmospheric pressure at
high altitudes allows
the water to boil
at a lower temperature
requiring a longer time
to cook.
Heat of Vaporization
 As you heat a substance, the temperature
increases. Once the substance begins to
change state from a liquid to a gas, the
temperature stops rising. The energy that is
being applied is being used for the state
change. Once the state change is complete,
the temperature will once again rise.
 Liquid water and water vapor have the same
Kelvin temperature during boiling.
Heat of Vaporization
Changes in Temperature as a solid is heated
gas
temp
liquid
solid
time
Heat of Vaporization is the amount of energy absorbed when 1kg of
liquid vaporizes at its normal boiling point
Heat of Vaporization
Changes in Temperature as a solid is heated
gas
temp
liquid
solid
time
What do the plateaus on the graph represent?
Heat of Fusion
 As you cool a substance, the temperature
decreases. Once the substance begins to
change state from a liquid to a solid, the
temperature stops decreasing. Once the
state change is complete, the temperature
will once again decrease.
Heat of Fusion
Changes in Temperature as a gas is cooled
temp
time
Heat of Fusion is the energy released as 1 kg of a substance
solidifies at its freezing point
 Melting point - The temperature of a
solid when its crystal lattice begins to
disintegrate and becomes a liquid
 Freezing point – The temperature of a
liquid when it begins to form a crystal
lattice and becomes a solid