Thermodynamics – branch of physics concerned
with the study of both thermal and mechanical
(or dynamical) concepts.
Application: Steam Engines in 1800’s
Topics Today: Internal Energy, Heat, and Work
Heat is defined as the transfer of energy across
the boundary of a system due to a temperature
difference between the system and its
surroundings.
What are the SI units of heat?
Internal energy is all the energy of a system that
is associated with its microscopic components—
atoms and molecules—when viewed from a
reference frame at rest with respect to the
center of mass of the system.
Equivalence between
mechanical energy
and internal energy
Figure adapted from Serway and Jewett, Physics for Scientists and Engineers, 8th ed.
Example:
An 80 kg person jumps off a 10 m high dive. How
many calories are produced as the water stops
the person?
Example:
A 70 g piece of aluminum (c = 0.215 cal/g°C) at
100°C is dropped into 100 g of water at 0°C. Find
the final temperature.
If equal amounts of heat are transferred into two
containers of water and the resultant temperature
change of the water in one container is twice that of
the water in the other container, what can you say
about the quantity of water in the two containers?
1. One container contains four times as much water.
2. One container contains twice as much water.
3. Both containers contain the same amount of water.
4. I need more information before I can say anything.
Two bodies that are not in thermal equilibrium
initially are placed in intimate contact. After a while
the
1. temperature of the cooler one will rise the same
number of Kelvins as the temperature of the hotter
one drops.
2. amount of thermal energy contained by both
bodies will be equal.
3. specific heats of the bodies will be equal.
4. thermal conductivity of each body will be the same
5. none of the above.
Everyone who has ever walked barefoot on a
beach in summer has noticed how fast the sand
gets hot in the morning. That’s because the sand
has a
1. light color.
2. fairly low specific heat.
3. fairly high specific heat.
4. high thermal conductivity.
5. low latent heat of fusion.
6. none of these.
Example:
A 2 kg lead ball (c = 128 J/kg°C) at 30°C is placed
on a large piece of ice (Lf = 3.33 x 105 J/kg). How
much ice melts?
From the graph below, determine the latent
heat of fusion of H20.
Figure adapted from Serway and Jewett, Physics for Scientists and Engineers, 8th ed.
An open beaker of pure water is gently boiling
at atmospheric pressure. A thermometer held
deep in the water will likely read a
temperature
1. a little greater than 100C.
2. equal to 100C.
3. equal to 212C.
4. a little less than 100C.
5. none of these.
An open pot of water is boiling on a gas stove when
someone raises the flame. The result will be
1. A substantial increase in the temperature of the
water.
2. An decrease in the pressure of the water.
3. An increase in the rate of boiling.
4. An appreciable increase in both the rate of boiling
and the temperature of the water.
5. None of these.
Five pound of ice in a cooler will keep things cold
longer than five pounds of ice water because
1. the ice is colder than the water.
2. the specific heat of ice is greater than the
specific heat of water.
3. five pounds of ice has more volume than five
pounds of water.
4. the heat capacity of water is less than the heat
capacity of ice.
5. none of the above.
When you put water at about 25C into an ice tray
and freeze it in the refrigerator,
1. more heat is removed in bringing the water to
the freezing point than is removed in the freezing
process.
2. more heat is removed in the freezing process
than in bringing the water to the freezing point.
3. about equal amounts of heat are removed in
brining the water to the freezing point and in
freezing the water.
From the graph below, determine the latent
heat of vaporization of H20.
Figure adapted from Serway and Jewett, Physics for Scientists and Engineers, 8th ed.
Can you boil water over a flame
in a paper cup?
1. yes.
2. no.
3. YOU MUST BE NUTS!
Work done by a gas:
Work done on a gas:
Example:
An ideal gas expands from 2.0 m3 to 3.0 m3 at
constant temperature. What is the work done
by the gas?
Below are plots of pressure vs. temperature for
a system that was taken from an initial state, i,
to a final state, f, along 3 different paths (i.e. in 3
different ways).
Was positive work done on or by the system?
Which path leads to the most work done on the
system?
You are planning a birthday party for your niece and need
to make at least 4 gallons of Kool-Aid, which you would
like to cool down to 32 oF (0 °C) before the party begins.
Unfortunately, your refrigerator is already so full of treats
that you know there will be no room for the Kool-Aid. So,
with a sudden flash of insight, you decide to start with 4
gallons of the coldest tap water you can get, which you
determine is 50 °F (10 °C), and then cool it down with a 1quart chunk of ice you already have in your freezer. The
owner's manual for your refrigerator states that when the
freezer setting is on high, the temperature is -20 °C. Will
your plan work? You assume that the density of the KoolAid is about the same as the density of water. You look in
your physics book and find that the density of water is 1.0
g/cm3, the density of ice is 0.9 g/cm3, the heat capacity of
water is 4200 J / (kg °C), the heat capacity of ice is 2100 J
/ (kg °C), the heat of fusion of water is 3.4 x 105 J/kg, and
its heat of vaporization is 2.3 x 106 J/kg.