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Problem 3.2
The formula of the molecule is C
3
H
6
Because the pressure is low (14.7 psia) the Ideal Gas Law can be used. Thus, calculate the
molecular weight as follows.
PV
nRT
m
m
PV
RT
M
RT
RT
M
V
ρ
=
=
=
=
3
3
0.103
(100
460)
10.73
42.10 l /
14.7
lb
psi ft
R
M
RT
b lb
mol
psi
ft
R lb
mol
+
=
=
=


o
o
The number of hydrogen atoms (2) for each carbon atom is given. Ttherefore, the general
formula of the molecule will have the form
C
n
H
2n
. With this information, the molecular weight
formula is set up:
( )
2
(
)
12
2
14
/
42.1
/
3
molecule
M
M C
n
M H
n
n
n
nlb lb
mole
lb lb
mole
n
=
+
=
+
=

=

=
Then, the formula of the molecule is
C
3
H
6
(Propene)
Problem 3.7
The porosity of the sandstone is 0.18 or 18%
Use the following equation in order to calculate porosity:
void
bulk
solid
bulk
bulk
V
V
V
Porosity
V
V

=
=
The Ideal Gas behavior is used to model the process taking place in the two cells. First,
there is gas at certain conditions of P & T in cell 1 occupying a volume V1Vs. Then, the valve is
opened and the gas expands at constant T to a new volume V2Vs where V2 is the sum of the
volumes of the two vessels. Then by difference, the solid volume of the sandstone is calculated and
with this information, the porosity is determined.
First, write the equation of an Ideal Gas for the initial
condition:
1 1
1
1
1
(5
)
P V
nRT
P
Vs
nRT
=

=
Second, write the Ideal Gas Law for the final condition
after the valve is opened:
2 2
1
2
1
(10
)
P V
nRT
P
Vs
nRT
=

=
Here, Vs is the solid volume of the sandstone.
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View Full DocumentThird, combine both equations as follows:
2 2
1 1
1
1
2
1
1
1
1
2
1
2
1
(10
)
(5
)
10
5
10 334.7 5 760
1.0651
334.7 760
P V
P V
T
T
P
Vs
P
Vs
T
T
P
P
Vs
P
P
Vs
cc
=


=

=


=
=

Now, the porosity is determined:
1.3 1.0651
0.18067 18%
1.3
void
bulk
solid
bulk
bulk
V
V
V
Porosity
V
V


=
=
=
=
Problem 3.11.
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 Spring '08
 Peters

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