Thermodynamics Worksheet
Directions: Write the answers to the following questions in the spaces provided. Where
appropriate, make complete statements.
1. What is thermodynamics?
Thermodynamics is the study of processes in which energy is transferred as heat and as
work.
2. What is internal energy?
The sum total of all the energy of the molecules of the system.
3. State the first law of thermodynamics.
The change of internal energy of a closed system will be equal to the heat added to the
system minus the work done by the system.
4. What is an adiabatic process?
One in which no heat is allowed to flow into or out of the system.
5. How does a heat pump differ from a heat source?
A heat pump is any device that changes thermal energy into mechanical work while a heat
source simply has a greater temperature than its environment.
6. What is an isothermal process?
Process carried out at a constant temperature.
7. What is an ideal heat engine?
A heat engine in which each of the processes of heat addition and exhaust, of gas
expansion or compression, were considered to be done reversibly.
8. What change in operating conditions increases the efficiency of an ideal heat engine?
Lowering the lower operating temperature or raising the higher operating temperature.
9. State the second law of thermodynamics.
Clausius statement: Heat flows naturally from a hot object to a cold object; heat will not flow
spontaneously from a cold object to a hot object.
Kelvin-Planck statement: No device is possible whose sole effect is to transform a given
amount of heat completely into work.
10. State the law of entropy.
The total entropy of any system plus that of its environment increases as a result of any
natural process. Natural processes tend to move toward a state of greater disorder.
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11. The mechanical equivalent of heat in the SI system is
4.186 J/cal.
4.186 J/cal
12. The first law of thermodynamics is a special case of the
law of conservation of energy.
conservation of energy
13. When heat is converted to another form of energy, or
vice versa, there is no loss of energy.
no
14. In the Joule experiment, no heat enters or leaves the
insulating jar. The water-churning process is, therefore,
an adiabatic one.
adiabatic
15. Work done by a gas is considered positive when the
gas expands and negative when the gas is
compressed.
expands
compressed
16. When the volume of a gas increases isothermally, its
pressure decreases and its temperature remains
constant.
decreases
remains constant
17. During an isothermal expansion, the internal energy
remains constant.
remains constant
18. When the volume of a gas increases adiabatically, its
pressure
and its
temperature
.
decreases
decreases
19. During an adiabatic expansion, the internal
energy
.
decreases
20. The source of the heat equivalent of work done by an
ideal gas during isothermal expansion is
its
, while the source of the heat equivalent
of work done by an ideal gas during adiabatic
expansion is its
.
heat input at high temperature
internal energy of the gas
21. Give an example of a heat pump:
.
steam engine
22. Work can be found by finding the
diagram.
of a
area under
PV curve
23. The second law of thermodynamics makes it impossible
to attain a temperature of
.
0K
24. Entropy is the amount of energy that cannot be
converted into
.
useful work
25. Natural processes tend to increase
universe.
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entropy
Thermodynamics
26. What happens to V, P, and T in the following processes?
Process
Isobaric expansion
V
increases
Isothermal compression decreases
Isobaric compression
decreases
P
T
remains constant
increases
increases
remains constant
remains constant
decreases
During which of the above processes is work done on the gas?
compression
During which of the above processes is work being done by the gas?
expansion
27. A gas expands from a volume of 2.00 m3 to 6.00 m3 and does 6912 joules of work against a
constant outside pressure. Find the outside pressure.
W = P ΔV
6912 J = P (6 m3 - 2 m3)
P = 1728 N/m2
28. A Carnot engine operates between 20 °C and 500 °C. How much energy must be supplied
to produce 10000 J of work?
e = 1 - TL / TH = 1 - (293 K / 773 K) = 0.62
e = W / QH
0.62 = 10000J / QH
QH = 16000 J
29. Find the efficiency of an ideal heat engine operating between temperatures of -100 °C and
500 °C.
e = 1 - TL / TH = 1 - (173 K / 773 K) = 0.78
30. How much would the efficiency of an ideal heat engine be improved if its lower temperature
were changed from 80.0 °C to 40.0 °C while the upper temperature remained at 300 °C?
e = 1 - TL / TH = 1 - (353 K / 573 K) = 0.38
e = 1 - TL / TH = 1 - (313 K / 573 K) = 0.45
0.45 - 0.38 = 0.07
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