Chapter 9 “Heat”
Honors Physics
Temperature
• Adding or removing energy
changes the temperature.
• Temperature is the average KE of
the atoms and molecules present.
High avg. KE = high temp.
• We use relative scales: ºF , ºC and
absolute scales: K
Temperature
• Internal energy (ΔU) is the
energy associated with atomic
motion and is proportional to the
substance's temperature.
• Temperature is changed by
adding or removing energy.
Temperature
Celsius-Fahrenheit Temperature
Conversions
Tf = 9/5 Tc + 32.0
Celsius-Kelvin Temperature
Conversions
T = Tc + 273.15
Concept Check
The lowest outdoor temperature
ever recorded on Earth is -128.6°F,
recorded at Vostok Station,
Antarctica in 1983. What is this
temperature on the Celsius and
Kelvin scales?
Concept Check
-89.2° C, 184 K
Concept Check
The temperatures of one
northeastern state range from
105° F in the summer to -25°F in
the winter. Express this
temperature range in degrees
Celsius and in kelvins.
Concept Check
41°C to -32°C, 314 K to 241 K
Concept Check
A pan of water is heated from 23°C
to 78°C. What is the change in its
temperature on the Kelvin and
Fahrenheit scales?
Concept Check
55 K, 99°F
Concept Check
Liquid nitrogen is used to cool
substances to very low
temperatures. Express the boiling
point of liquid nitrogen (77.34 K at
1 atm of pressure) in degrees
Celsius and in degrees Fahrenheit.
Concept Check
-195.81°C, -320.5°F
Heat
• Heat is the energy transferred
between objects due to the
difference in their temperatures.
• Heat will naturally go from
objects of high KE to objects of
low KE. To go in the opposite
direction requires work.
Thermal (Heat) Units
• We’ll be mostly using joules (J)
or calories (cal). However, you
should be aware that there are
others (p 307).
• 1 calorie is equal to the amount
of energy required to heat 1
gram of water from 4º to 5 ºC.
• 1 cal = 4.184 J
Total energy is
conserved.
• Conservation of energy states
that the sum of the change in
the potential energy and the
change in kinetic energy and
the change in internal energy
must equal zero.

 PE +  KE +  U = 0
Concept Check
Consider an arrangement similar
to the one used to demonstrate
energy conservation on p.310. If a
total mass of 11.5 kg falls 6.69 m
and all of the mechanical energy
is converted to internal energy, by
how much will the internal energy
of the water increase?
Concept Check
755 J
Concept Check
A worker drives a 0.500 kg spike
into a rail tie with a 2.50 kg
sledgehammer. The hammer hits
the spike with a speed of 65.0 m/s.
If one-third of the hammer's
kinetic energy is converted to the
internal energy of the hammer and
spike, how much does the total
internal energy increase?
Concept Check
1.76 x 103 J
Concept Check
A 3.0 x 10-3 kg copper penny drops
a distance of 50.0 m to the
ground. If 65% of the initial
potential energy goes into
increasing the internal energy of
the penny, determine the
magnitude of that increase.
Concept Check
0.96 J
Concept Check
The amount of internal energy
needed to raise the temperature
of 0.25 kg of water by 0.2ºC is
209.3 J. How fast must a 0.25 kg
baseball travel in order for its
kinetic energy to equal this
internal energy?
Concept Check
41 m/s
Calorimetry
• We can calculate the amount of
the change in internal energy
through calorimetry.
• The equation Q = mct is used.
• Q = internal energy change
• m = mass
• Cp = specific heat (unique)
 t = change in temperature.
Heat lost = Heat gained
• In an insulated situation (no
heat escapes into the
surroundings):
Q lost = -Q gained
• m1cp1t1 = -m2cp2t2
Calorimetry
• Generally, we use water as the
substance that gains the heat
since the specific heat of water
is known.
Concept Check
What is the final temperature
when a 3.0 kg gold bar at 99ºC is
dropped into 0.22 kg of water at
25ºC? (Use the table on p.314.)
Concept Check
47ºC
Concept Check
A 0.225 kg sample of tin initially at
97.5ºC is dropped into 0.115 kg of
water. The initial temperature of
the water is 10.0ºC. If the specific
heat capacity of tin is 230 J/kg*ºC,
what is the final equilibrium
temperature of the tin-water
mixture?
Concept Check
18ºC
Concept Check
Brass is an alloy made from
copper and zinc. A 0.59 kg brass
sample at 98.0ºC is dropped into
2.80 kg of water at 5.0ºC. If the
equilibrium temperature is 6.8ºC,
what is the specific heat capacity
of brass?
Concept Check
390 J/kg*ºC
Concept Check
A hot, just minted copper coin is
placed in 101 g of water to cool.
The water temperature changes
by 8.39ºC, and the temperature of
the coin changes by 68.0ºC. What
is the mass of the coin?
Concept Check
135 g
Phase Changes
• Phase changes occur when an
object goes from one phase of
matter to another.
• When an object is going through
a phase change, added energy
is used to make the change
without raising the temperature.
This is latent heat.
Equations for Phase
Changes.
• During heating (temperature
change) use
Q = mct
• During phase changes use heat
of fusion or heat of vaporization.
• Q = mLf or Q = mLv
• L = latent heat (unique)
Heating curve of water
• Starting with ice at -4 º C and
going to steam at 120 ºC.
120 º C
100 º C
steam
liquid
0ºC
-4 º C
ice
Adding energy
Types of Heat Transfer
• Thermal Conduction-requires objects
to touch in order to transfer heat.
• Convection-requires the motion of a
fluid between objects in order to
transfer heat.
• Radiation-energy moves in the form
of electromagnetic radiation in order
to transfer heat.
Conduction vs insulation
• The ability to conduct heat is a
gradient from good conductors
such as metals to poor
conductors such as ceramics or
plastics. Poor conductors are
good insulators. An insulator
doesn’t actually inhibit
conduction, it is just a poor
conductor.