Define, in your own words, the following:
1. Temperature
2. Heat
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Mr. Szwast has meetings after school on the
following days, and therefore will not be
available:
Wednesday, February 3
Monday, February 8
Chapter 12
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What is the difference between a hot object
and a cold object?
Temperature is a measure of the average
kinetic energy of the particles of an object.
The molecules of a hot object are moving
faster than their counterparts in a cold object.
Does not depend on the mass of the object.
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Thermal energy is a measure of the total
kinetic energy of the particles of an object.
Thermal energy depends on the mass of the
object, while temperature does not.
Thermal energy is one component of the
internal energy of an object, and the only part
of internal energy we will discuss in this
class.
Is a form of potential energy.
Represented by 𝑈𝑇 .
Measured in Joules, J.
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The kinetic energy of an object depends on
the speed of the whole object.
The temperature of an object depends on the
average speed of the individual particles that
make up the object.
The thermal energy of an object depends on
the temperature and the mass of the object.
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The SI unit of temperature is the Kelvin,
represented by a capital K.
The Kelvin scale has no negative
temperatures: 0 K is absolute zero. Nothing
can be colder than 0 K
Temperatures can easily be converted
between Celsius and Kelvin
TK  TC  273.15
TC  TK  273.15
1)
Convert to Kelvin
a) 25˚C (approximate room temperature)
b) 100.00˚C (boiling point of water)
c) 37˚C (average body temperature of a human)
2)
Convert to Celsius
a) 2 K (Approximate temperature of interstellar
space)
b) 700. K (Approximate temperature of the surface
of Venus)
c) 300. K (A warm summer day)
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Energy that is transferred between objects is
called heat.
Heat always flows from hotter objects to
colder objects.
Heat is represented by a capital “Q”
The unit of heat, like all energy, is the Joule, J
Heat can be transferred in three ways:
◦ Conduction
◦ Convection
◦ Radiation
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Conduction is the transfer of thermal energy
through collision of particles.
Conduction spreads thermal energy through
an object.
Heat can also be conducted from one object
to another object in direct contact.
◦ Hot electric stove to a pot
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The motion of a fluid (liquid or gas) caused
by temperature differences is called
convection.
The motion of the fluid transfers heat faster
than conduction alone.
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Radiation is the transfer of energy by
electromagnetic waves.
Radiation does not depend on the presence
of matter.
The sun heats the earth through radiation
1)
Convert to Kelvin
a) 16˚C (Today’s predicted high temperature in
San Diego)
b) -3.3˚C (Last night’s low temperature in
Punxsutawney, PA)
c) 1528˚C (The melting point of iron)
d) 5500˚C (Approximate temperature of the sun’s
photosphere)
e) 1.5x107 ˚C (Approximate temperature of the
sun’s core)
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Heat is transferred from a hotter object to a
colder object.
This is done until the objects are at the same
temperature.
Thermal equilibrium is reached when the
objects have reached the same temperature.
At thermal equilibrium, the amount of heat
from AB equals the heat from BA.
There is still heat transfer, but it is balanced,
like balanced forces.
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The specific heat capacity of a material (in SI
units) is the amount of heat needed to raise 1
kg of the material by 1 K.
Often called “specific heat” or “heat capacity”
The specific heat capacity of a material is
measured in Joules per kilogram per Kelvin,
J
kg  K
Specific heat is represented by “C”
Specific heats vary widely from one material
to another
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The amount of heat transferred is equal to
the mass of the object times the specific heat
of the object times the difference between
final and initial temperatures.
Q  mCT  mC T f  Ti 
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Since Celsius and Kelvin have the same
temperature interval, you can use either for
this equation (but not equations we’ll see
later).
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A 5.00 kg cast iron skillet is heated on the
stove from 300. K to 450. K. How much heat
had to be transferred into the iron skillet?
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When you turn on the hot water to wash
dishes, the water pipes absorb some of the
heat from the hot water. What is the mass of
the pipes if they are made of copper and
absorb 100. kJ when the temperature is
raised from 25˚C to 75˚C?
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Suppose you drink 0.20 kg of water at 20.˚C.
Once inside your stomach, it absorbs heat
until it reaches 37˚C. How much heat did the
water absorb from your body?
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52500 J of heat are transferred into an 8.25 kg
block of lead, raising its temperature to 340. K.
What was its initial temperature?
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Read pages 313-318
Page 319 #3-5
Page 322 #10-13
Read pages 319-322
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750 kJ of heat are transferred from a stove to a
13 kg cast-iron pan. If its initial temperature is
21°C, what is its final temperature?
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A calorimeter is a device used to measure
changes in thermal energy.
A calorimeter provides a closed, isolated
system.
A simple calorimeter contains a hot test
substance and a known mass of cold water.
More complex calorimeters are used to
measure chemical reactions and energy
content of food.
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Heat is transferred from the hot object to the
cold object
No heat is lost; Any heat taken from the hot
object must go to the cold object.
◦ (Technically, the calorimeter absorbs some of the
heat, but we will often neglect it).
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A 25.0 g piece of copper at 175°C is dropped
into a calorimeter containing 500. g of water
at 25.0°C. What is the final temperature of
the water?
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Read Section 12.1 (pages 313-322)
Page 321 #6-9
Page 336 #36-40, 52-60
Read Section 12.2 (pages 323-331)
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Solid, liquid, and gas are the most common
states of matter
An exchange of heat is required to change
the state of matter
SolidLiquidGas requires heat flow into the
object
GasLiquidSolid requires heat flow out of
the object
Changes of state of a pure substance occur at
a constant temperature
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The melting point of a substance is the
temperature at which it changes between a
solid and a liquid.
◦ The same as the freezing point.
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The boiling point of a substance is the
temperature at which it changes between a
liquid and a gas.
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The heat of fusion is the amount of energy
needed to melt 1 kg of a substance
Same amount of heat must be lost to freeze
1 kg of a substance
Represented by a capital 𝐻 with a subscript
lower-case 𝑓, 𝐻𝑓.
Measured in Joules per kilogram, J/kg
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The heat required to melt a solid is equal to
the mass of the solid times the heat of
fusion
Qmelt  mH f
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The heat loss required to freeze a liquid is
equal to the mass of the liquid times the
heat of fusion.
Q freeze  mH f
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How much heat is required to melt 35 g of ice
at 273 K? The heat of fusion of water is
3.34x105 J/kg.
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It takes 26.8 kJ to melt 425 g of gold at its
melting point. What is the heat of fusion of
gold?
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The heat of vaporization is the amount of
energy needed to vaporize 1 kg of a substance
Same amount of heat must be lost to
condense 1 kg of a substance
Represented by a capital 𝐻 with a subscript
lower-case 𝑣, 𝐻𝑣.
Measured in Joules per kilogram, J/kg
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The heat required to vaporize a liquid is equal
to the mass of the liquid times the heat of
vaporization
Qvaporize  mH v
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The heat loss required to condense a gas is
equal to the mass of the gas times the heat of
vaporization
Qcondense  mH v
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A pot of water is boiling on the stove. How
much heat is required to vaporize 725 g of
water? The heat of vaporization of water is
2.26x106 J/kg.
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A sample of 25 grams of liquid methanol is
heated to its boiling point. It takes 22 kJ
more heat to vaporize the methanol. What is
the heat of vaporization of methanol?
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A 1.000 kg block of water ice is originally at
-20.0°C. It is heated to its melting point
(0.000°C), melted, heated to its boiling point
(100.00°C), vaporized, and then heated to
140.0°C.
How much total heat did the water absorb?
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The change in thermal energy of an object is
equal to the heat added to the object minus
the work done by the object/system.
U  Q  Wby the system
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The work done by the system is equal in
magnitue to the work done to the system, but
in the opposite direction
U  Q  Won the system
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A heat engine is a device that is able to
continuously convert thermal energy into
mechanical energy (work)
Requires a high temperature (TH) source of
thermal energy (QH), called the input heat
Requires a low temperature (TL) sink of
thermal energy (QL), called the waste heat
Creates work based on heat in and out
W  QH  QL
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An automobile internal combustion engine is
one example of a heat engine
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A heat engine removes 825 J of thermal
energy from a high temperature source and
produces 421 J of work. How much waste
heat is produced?
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A heat engine removes 737 J of thermal
energy from a high temperature source and
produces 583 J of waste heat. How much
work does the engine produce?
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The efficiency of a heat engine is equal to the
ratio of work done to input heat
W
QH  QL
QL
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 1
QH
QH
QH
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Efficiency is a unitless number between zero
and one, 0    1
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A refrigerator is the reverse of a heat engine
Requires an input of work to move thermal
energy from a colder system to a warmer
system.
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Entropy is the measure of disorder in a system.
Entropy is represented by a capital S
Entropy has units of Joules per Kelvin, J/K
The entropy of the universe is always
increasing.
The change in entropy of an object/system is
equal to the heat added to the object divided
by the temperature of the object in Kelvins
Q
S 
T
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Entropy increases if:
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Heat is added
Things get mixed together
A solid melts
A liquid evaporates
Something breaks or spills
Entropy decreases if:
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Heat is removed
Things get separated
A gas condenses
A liquid freezes
Something is put in a more orderly form
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The 2nd Law of Themodynamics states the
following:
Natural processes go in the direction that
maintains or increases the total entropy.
Heat will never flow from a cold object to a
hot object without external work.
State whether each of the following processes
causes entropy to increase or decrease:
1. Cleaning your room
2. Ice melting
3. Mixing cooking ingredients together
4. A baseball smashing a window
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State whether each of the following processes
causes entropy to increase or decrease:
1. Hot lava turning to igneous rocks
2. Putting sugar and cream in coffee
3. Putting cluttered files away in a filing
cabinet
4. Using a pile of Legos to build a miniature
house
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Read Chapter 12
Page 319 #3-5; Page 322 #10-13
Page 321 #6-9; Page 336 #36-40, 52-60
Page 325 #19-21; Page 328 #22-26
Page 336 #35, 41-44, 61-73
Chapter 12 Study Guide
Design a Lab (details coming soon)