Example 32
A gas with a molecular weight of 147 is compressed
isothermally and reversibly in a pistoncylinder assembly
from an initial pressure of 60 kPa to a final pressure of
180 kPa. The initial volume and temperature are 344 cm
3
and 10°C. Determine
a) the heat transferred
b) the work done
Solution:
a) For a reversible process
()
21
QT
S
S
=−
For an ideal gas, the entropy change is
22
11
ln
ln
p
TP
R
ssc
TMP
⎛⎞
−=
−
⎜⎟
⎝⎠
Since
12
TT
=
, this reduces to
2
1
kJ
8.314
180 kPa
kJ
kmol K
ln
ln
0.0621
kg
60 kPa
kg K
147
kmol
P
R
ss
MP
⋅
−
=
−
=
−
⋅
Qm
T
s
s
To find the mass, use the ideal gas law
1
PVM
m
RT
=
3
3
1 m
kg
60 kPa
344 cm
147
100 cm
kmol
0.00129 kg
kJ
8.314
10
273 K
kmol K
m
⎛
⎞
⎜
⎟
⎝
⎠
==
+
⋅
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 Spring '08
 Kaminski
 Thermodynamics, Entropy, 0.0227 kJ, 0.0621 kg

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