lim (kl9356) – Extra Credit Homework 23 – Weathers – (17104)
1
This printout should have 15 questions.
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the next column or page – fnd all choices
beFore answering.
001
(part 1 oF 2) 10.0 points
Given:
R
= 8
.
31451 J
/
K
·
mol
.
How much work is done by the steam when
1
.
1 mol oF water at 100
◦
C boils and becomes
1
.
1 mol oF steam at 100
◦
C at 1
.
3 atm pres
sure?
Correct answer: 3411
.
18 J.
Explanation:
Given :
n
= 1
.
1 mol
,
R
= 8
.
31451 J
/
K
·
mol
,
T
= 100
◦
C = 373 K
,
m
= 18 g
/
mol
,
P
= 1
.
3 atm
and
ρ
= 1 g
/
cm
3
.
Using the ideal gas law,
P V
=
nRT .
m
is the molar mass oF water.
The work done is
W
=
P
Δ
V
=
nRT
−
n
p
mP
ρ
P
= (1
.
1 mol) (8
.
31451 J
/
K
·
mol) (373 K)
−
(1
.
1 mol)
(18 g
/
mol) (1
.
3 atm)
1 g
/
cm
3
×
±
m
100 cm
²
3
1
.
013
×
10
5
Pa
1 atm
= 3411
.
18 J
.
002
(part 2 oF 2) 10.0 points
±ind the change in internal energy oF the
steam as it vaporizes.
Consider the steam
to be an ideal gas with heat oF vaporization
2
.
26
×
10
6
J
/
kg.
Correct answer: 41
.
3368 kJ.
Explanation:
Given :
L
v
= 2
.
26
×
10
6
J
/
kg
The heat needed to vaporize the water is
Q
=
nmL
v
±rom the frst law oF thermodynamics
Δ
U
=
Q
−
W
=
v
−
W
=
b
(1
.
1 mol) (18 g
/
mol)
1 kg
1000 g
×
(2
.
26
×
10
6
J
/
kg)
−
3411
.
18 J
B
1 kJ
1000 J
= 41
.
3368 kJ
.
003
10.0 points
One mole oF an ideal gas is heated at constant
pressure so that its temperature increases by a
Factor oF 8. Then the gas is heated at constant
temperature so that its volume increases by a
Factor oF 8.
±ind the ratio oF the work done during the
isothermal process to that done during the
isobaric process.
Correct answer: 2
.
3765.
Explanation:
Given :
k
= 8
.
The work done in the isobaric process is
W
ab
=
i
b
a
P dV
=
P
a
(
V
b
−
V
a
)
=
nR
(
k T
a
)
−
a
= (
k
−
1)
a
,
The work done in the isothermal process is
W
bc
=
i
c
b
P dV
=
b
i
c
b
dV
V
=
b
ln
p
V
c
V
b
P
=
(
k T
a
) ln
k ,
ThereFore the ratio Fraction is
r
=
W
bc
W
ab
=
(
k T
a
) ln
k
(
k
−
1)
a
=
k
ln
k
k
−
1
=
8 ln(8)
(8
−
1)
= 2
.
3765
.
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004
10.0 points
The surface of the Sun has a temperature of
about 5741 K.
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 Fall '08
 Weathers
 Magnetism, Work, lim, Correct Answer, EXTRA CREDIT HOMEWORK

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