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
Slide 3
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
Slide 4
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
Slide 5
The Kelvin Scale A zero reading on the Celsius or Fahrenheit
scales does NOT correspond to zero kinetic energy - atoms are still
moving at O o C (freezing) and O o F (its below freezing, but atoms
are still moving!) K o C o F _____373_______100_______
212__________________boiling pt. (water)
_____273_______0__________32__________________freezing pt. (water)
_____0_________-273_______-459_________________Absolute zero
Slide 6
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) }
Slide 7
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: T k = (T c + 273) K
Slide 8
Temperature Conversions Similarly, a Kelvin reading can be
expressed as a celsius reading by subtracting 273: T c = (T k 273)
o C
Slide 9
Temperature Conversions T k = (T c + 273) KT c = (T k 273) o C
Complete the following conversions using the equations above:
TemperatureCelsiusKelvin Melting point of iron1808 Household
oven350 Food freezer255 Sublimation point of dry ice -78.5 Boiling
point of nitrogen77.4
Slide 10
Temperature Conversions T k = (T c + 273) KT c = (T k 273) o C
Complete the following conversions using the equations above:
TemperatureCelsiusKelvin Melting point of iron15351808 Household
oven350623 Food freezer-18255 Sublimation point of dry ice
-78.5194.5 Boiling point of nitrogen-195.677.4
Slide 11
Because Fahrenheit degrees are smaller than Celsius degrees the
conversion equation is a bit more complex: o C=5/9( o F-32) o F=9/5
o C + 32 Temperature Conversions
Slide 12
o C=5/9( o F-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 o F into
celsius:
Slide 13
Temperature Conversions o F=9/5 o C + 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 22 o C into
Fahrenheit:
Slide 14
Temperature Conversions o C=5/9( o F-32) o F=9/5 o C + 32 Using
the above equations, convert the following:
TemperatureCelsiusFahrenheit A warm day25 Body temperature98.6 Room
temperature20 Freezing point of water32
Slide 15
Temperature Conversions o C=5/9( o F-32) o F=9/5 o C + 32 Using
the above equations, convert the following:
TemperatureCelsiusFahrenheit A warm day2577 Body temperature3798.6
Room temperature2068 Freezing point of water032
Slide 16
HOMEWORK Complete the Temperature Conversions worksheet for
TOMORROW
Slide 17
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
Slide 18
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.
Slide 19
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
Slide 20
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
Slide 21
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?
Slide 22
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.
Slide 23
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.
Slide 24
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
Slide 25
Sublimation Dry ice (solid CO 2 ) 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.
Slide 26
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
Slide 27
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.
Slide 28
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.
Slide 29
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
Slide 30
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.
Slide 31
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.
Slide 32
Vapor Pressure and Boiling THINK ABOUT IT! Why do foods cooked
in boiling water at higher altitudes need to be cooked LONGER?
Slide 33
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.
Slide 34
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.
Slide 35
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
Slide 36
Heat of Vaporization Changes in Temperature as a solid is
heated gas temp liquid solid time What do the plateaus on the graph
represent?
Slide 37
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.
Slide 38
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
Slide 39
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
