Define, in your own words, the following: 1. Temperature 2. Heat
Mr. Szwast has meetings after school on the following days, and
therefore will not be available: Wednesday, February 3 Monday,
February 8 Chapter 12 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. 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. 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 1) Convert to Kelvin a)25C (approximate room
temperature) b)100.00C (boiling point of water) c)37C (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)
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 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 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. 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)16C (Todays predicted high temperature in San Diego)
b)-3.3C (Last nights low temperature in Punxsutawney, PA) c)1528C
(The melting point of iron) d)5500C (Approximate temperature of the
suns photosphere) e)1.5x10 7 C (Approximate temperature of the suns
core) 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. 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, Specific heat is represented by C Specific
heats vary widely from one material to another 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. Since Celsius and Kelvin have the same temperature
interval, you can use either for this equation (but not equations
well see later). 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? 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 25C to 75C? Suppose you drink
0.20 kg of water at 20.C. Once inside your stomach, it absorbs heat
until it reaches 37C. How much heat did the water absorb from your
body? J of heat are transferred into an 8.25 kg block of lead,
raising its temperature to 340. K. What was its initial
temperature? Read pages Page 319 #3-5 Page 322 #10-13 Read pages
750 kJ of heat are transferred from a stove to a 13 kg cast-iron
pan. If its initial temperature is 21C, what is its final
temperature? 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. 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). A 25.0 g piece of copper at 175C is dropped into a calorimeter
containing 500. g of water at 25.0C. What is the final temperature
of the water? Read Section 12.1 (pages ) Page 321 #6-9 Page 336
#36-40, Read Section 12.2 (pages ) 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 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. The boiling point of a substance is the temperature
at which it changes between a liquid and a gas. A hot cup of coffee
is left out on a counter. When it is put down, its temperature is
72C. When it is picked up 15 minutes later, its temperature is 51C.
The mass of the coffee is 0.31 kg. Assume the specific heat
capacity of coffee is the same as water. How much heat was
transferred out of the coffee? What mode(s) of heat transfer were
responsible for the heat loss? The heat required to melt a solid is
equal to the mass of the solid times the heat of fusion The heat
loss required to freeze a liquid is equal to the mass of the liquid
times the heat of fusion. How much heat is required to melt 35 g of
ice at 273 K? The heat of fusion of water is 3.34x10 5 J/kg. It
takes 26.8 kJ to melt 425 g of gold at its melting point. What is
the heat of fusion of gold? The heat required to vaporize a liquid
is equal to the mass of the liquid times the heat of vaporization
The heat loss required to condense a gas is equal to the mass of
the gas times the heat of vaporization 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 2.26x10 6 J/kg. 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? 3.5 kg of iron is heated to its melting
point. How much additional heat would be required to melt the iron?
Data about iron: A kg block of water ice is originally at -20.0C.
It is heated to its melting point (0.000C), melted, heated to its
boiling point (100.00C), vaporized, and then heated to 140.0C. How
much total heat did the water absorb? 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. The work done by the system is
equal in magnitue to the work done to the system, but in the
opposite direction A heat engine is a device that is able to
continuously convert thermal energy into mechanical energy (work)
Requires a high temperature (T H ) source of thermal energy (Q H ),
called the input heat Requires a low temperature (T L ) sink of
thermal energy (Q L ), called the waste heat Creates work based on
heat in and out An automobile internal combustion engine is one
example of a heat engine 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? 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? The efficiency
of a heat engine is equal to the ratio of work done to input heat
Efficiency is a unitless number between zero and one, 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. 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 Entropy
increases if: Heat is added Things get mixed together A solid melts
A liquid evaporates Something breaks or spills Entropy decreases
if: Heat is removed Things get separated A gas condenses A liquid
freezes Something is put in a more orderly form A beaker contains
150 g of water at 22C. The water is heated to 75C. How much heat
must be added to the water to accomplish this? Water data: The 2 nd
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
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 Read Conceptual Physics Chapter 21 (pages ) Answer page 322
review questions #1-18 Homework: Page 336 #52-54, 61-63 Read
Chapter 12 Page 319 #3-5; Page 322 #10-13 Page 321 #6-9; Page 336
#36-40, Page 325 #19-21; Page 328 #22-26 Page 336 #35, 41-44,
Chapter 12 Study Guide Design a Lab (details coming soon)
