Herriman High Honors Physics
Chapter 9
Temperature and Heat
Herriman High Honors Physics
Temperature Scales Temperature is defined as a
measure of the average kinetic energy of the molecules.
Temperature scales were developed using the freezing and boiling points of water at sea level as the standard reference points.
Herriman High Honors Physics
Temperature Scales There are three Temperature
Scales used in Science Fahrenheit – Used primarily in the
United States Celsius – the standard for the Metric
System Kelvin – Also know as the “Absolute
Zero” Scale.
Herriman High Honors Physics
Standard Reference Points
Scale Boiling Point
Freezing Point
Fahrenheit 212 °F 32 °F
Centigrade 100 °C 0 °C
Kelvin 373 273
Herriman High Honors Physics
Conversion Equations Fahrenheit to Centigrade
C = 5/9 (F – 32)Ex: C = 5/9 (212-32) = 100
Centigrade to FahrenheitF = (9/5 C) + 32Ex: F = (9/5)(100) + 32 = 212
Herriman High Honors Physics
Conversion Equations Centigrade to Kelvin
K = C +273Ex: K = 100 + 273 = 373
Kelvin to Centigrade C = K - 273Ex: K = 373 - 273 = 100
You TryPractice
Set AP. 303
#1,3,& 5
Herriman High Honors Physics
Heat Heat is a form of Energy Transfer Heat flows from areas of high
energy to areas of lower energy Heat is transferred three way
Conduction – requires contact Convection – mass movement of
molecules Radiation – transfer over a distance
Heat Heat has the units of Energy
English System – calories – the amount of energy required to raise the temperature of 1 gram of water 1°C.
Metric System – Joule – 4.18 Joules in one calorie.
Herriman High Honors Physics
Conservation of Energy ΔPE + ΔKE + ΔU = 0
The change in potential energy + the change in kinetic energy + the change in internal energy = 0
Energy is not created or destroyed, it just changes form.
Herriman High Honors Physics
Practice BP. 311
Problems 2 & 4
Herriman High Honors Physics
Thermal Expansion Most objects tend to expand when
their temperature rises and to contract when the temperature drops.
Do you know what the one notable exception is?
Herriman High Honors Physics
Thermal Expansion Objects can expand linearly whereas
liquids expand volumetrically! Each substance has a constant for
which describes its ability to expand. Linear constants are denoted by the
Greek letter alpha, α and the volumetric constant is denoted by the Greek letter beta, β.
Herriman High Honors Physics
Conduction
Each material has an innate ability to absorb or give off heat – specific heat
The amount of heat an object can transfer depends upon three things: The mass of the object, m, (in Kg) The specific heat of the object, Cp, ( in J/g°C) The temperature change of the object, t, (in
ºC)
Herriman High Honors Physics
Calorimetry The symbol for heat is a capitol Q Law of Conservation of Energy
says thatQlost= Qgained
Mathematically Q = mCpΔt
Herriman High Honors Physics
Sample Problem How much energy is required to
raise the temperature of 5 Kg of water from 0°C to 100°C ? (Cp = 4186 J/kg°C)
Q= m CpΔt =
(5 kg)(Cp = 4186 J/kg°C)(100°C)
= 2093000 Joules
Herriman High Honors Physics
Sample Problem A 5 Kg copper ball is heated to 180
ºC and dropped into a container of water at 100 °C. When the temperature of the ball/water system equalizes the final temperature is found to be 110 ºC. How much water is in the container? (Cp= 390 J/Kg°C)
Herriman High Honors Physics
Solution
Qlost=Qgained
Q copper = Q water
mC copperΔt = mC water Δt
(5 kg)(390 J/Kg°C)(70°C)=m(4186 J/Kg°C)(10°C)
m = 3.26 kg Practice Cp. 316
Problems 1 & 3
Herriman High Honors Physics
Phases Changes Phase changes require that a
substance absorb energy or release energy to occur.
There is NO Change in Temperature associated with a phase change!
Different words are used to denote direction when dealing with a phase change.
Herriman High Honors Physics
Vocabulary of a Phase Change Freezing – change from liquid to solid.
Energy is released! Melting – change from solid to liquid
Energy is absorbed!
Both of these changes happen at the same point; 0° for water!
Herriman High Honors Physics
Vocabulary of a Phase Change Condensing – change from gas or
vapor to a liquid. Energy is released!
Boiling – change from liquid to gas or vapor Energy is absorbed!
Vapor is the gas phase of any substance which is normally a liquid at room temperature!
Herriman High Honors Physics
Energy Required for a Phase Change
Just like specific heat is a set amount of energy for each substance – the amount of energy required for a phase change is also substance specific.
Heat of Fusion – ΔHf , is the amount of energy absorbed or released when a substance melts or freezes!
Herriman High Honors Physics
Energy Required for a Phase Change
Heat of Vaporization – ΔHv , is the amount of energy absorbed or released when a substance boils or condenses!
Mathematically:Q = mΔHf for Fusion
orQ = mΔHv for Vaporization
Herriman High Honors Physics
Sample Problem
How much heat is required to melt 5 kg of ice at 0° C?
SolutionQ = mΔHf = (5 kg)(3.33 x 105 J/kg) =
1.665 x 106 J
Herriman High Honors Physics
Phase Diagram
Ice
Ice - Water
Water
Water-Steam
Steam
-5
0
100
120
Herriman High Honors Physics
Sample ProblemHow much energy is required to
convert 5 kg of ice at -5 °C to Steam at 120 °C?
StepsRaise temperature of ice to melting point
Melt IceRaise temperature of Water to boiling point
Vaporize WaterRaise Temperature of Steam to 120 °C
Herriman High Honors Physics
Solution
Step 1: Raise temperature of IceQ = mCΔt = (5 Kg)(2100 J/kg°C)(5 °C)= 52500 J
Step 2: Melt IceQ = mΔHf = (5 Kg)(3.33 x 105 J/kg) = 1665000 JStep 3: Raise temperature of water to boiling
Q = mCΔt = (5 Kg)(4186 J/kg°C)(100 °C)= 2093000 JStep 4: Vaporize Water
Q = mΔHv = (5 Kg)(22.6 x 105 J/kg) = 11300000 JStep 5: Raise temperature of Steam to 120°C
Q = mCΔt = (5 Kg)(2010 J/kg°C)(20 °C)= 201000 JStep 6: Get Total
Qtotal= 52500 + 1665000 + 2093000 + 11300000 + 201000 = 15311500J
Herriman High Honors Physics
Convection & Radiation Convection – transfer of energy by
mass movement of molecules Most common form is Wind
Radiation – transfer of energy through waves – most common form is light or electromagnetic waves
Will discuss both in more detail in later chapters
Herriman High Honors Physics
Problem Types Temperature Scales and
Conversions Thermal Expansion Conduction
Calorimetry Latent Heat
Fusion Vaporization