4 Thermodynoamics Exercises
4 Thermodynoamics Exercises
4 Thermodynoamics Exercises
Exercises
Thermodynamics
The First Law of Thermodynamics
(a)
U Q W
(b)
U Q W
Find (a) the change in internal energy and (b) the work done by the
gas.
U U f U i Q W U 32 nRT
The First Law of Thermodynamics
(a)
U 32 nRT f 32 nRTi
3
2
3.0 mol 8.31 J mol K 350 K 540 K 7100 J
W PV
2.0 105 Pa 1.0 10 8 m3 0.0020J
Q mcT 0.0010 kg 4186 J kg C 31 C 130 J
Thermal Processes
W 8.9 2.0 105 Pa 1.0 10 4 m 3
180 J
Thermal Processes Using and Ideal Gas
Vf
(a) W nRT ln
Vi
0.050 m 3
2.0 mol 8.31 J mol K 298 K ln 3400 J
3
0.025 m
(c) U Q W
Q W 3400 J
Heat Engines
W
e QH W QC
QH
W
QH
e
Heat Engines
QH W QC
W
QH
e
QC QH W
W 1
QC W W 1
e e
1
2510 J 1 8900 J
0.220
Carnots Principle and the Carnot Engine
Water near the surface of a tropical ocean has a temperature of 298.2 K, whereas
the water 700 meters beneath the surface has a temperature of 280.2 K. It has
been proposed that the warm water be used as the hot reservoir and the cool water
as the cold reservoir of a heat engine. Find the maximum possible efficiency for
such and engine.
TC
ecarnot 1
TH
15.9 Carnots Principle and the Carnot Engine
TC 280.2 K
ecarnot 1 1 0.060
TH 298.2 K
Carnots Principle and the Carnot Engine
QC
Refrigerator or Coefficien t of performanc e
air conditioner W
Refrigerators, Air Conditioners, and Heat Pumps
An ideal, or Carnot, heat pump is used to heat a house at 294 K. How much
work must the pump do to deliver 3350 J of heat into the house on a day when
the outdoor temperature is 273 K?
QC TC TC
QC QH
QH TH TH
W QH QC
TC
W QH 1
TH
Refrigerators, Air Conditioners, and Heat Pumps
TC 273 K
W QH 1 3350 J 1 240 J
TH 294 K
heat QH
pump Coefficien t of performanc e
W
Entropy
QC QH 1200 J 1200 J
S universe 1.6 J K
TC TH 350 K 650 K
Entropy
TC W
ecarnot 1 e
TH QH
Entropy
TC 150 K
(a) ecarnot 1 1 0.77
TH 650 K
TC 150 K
(b) ecarnot 1 1 0.57
TH 350 K