PHYS408
Fall 2008
Mastering Physics Assignment #3
Solutions
Problem 16.8
An element in its solid phase has mass density 1750 (kg)/m
3
and number density 4.39 *
10
28
(atoms)/ m
3
. (a) What is the element's atomic mass number?
If we have
one meter cubed of the element, then there would be
4.39
×
10
28
atoms.
The
number of moles would then be
n
=
4.39
×
10
28
N
A
=
4.39
×
10
28
6.02
×
10
23
/
mol
=
72924
mol
This would mass
1750
kg
, so the mass of one mole would be
1750
kg
72924
mol
=
0.024
kg
=
24
g
so
A
=
24
.
Problem 16.18
A gas at 100 degree(s) C fills volume V
0
.
(a) If the pressure is held constant, what is the volume if the Celsius temperature is
doubled?
This is a simple application of the ideal gas law.
pV
=
nRT
V
T
=
nR
p
=
constant
so
V
0
T
0
=
V
1
T
1
Of course, the temperatures have to be in Kelvins, so
T
0
=
100
o
C
=
373
K
T
1
=
200
o
C
=
473
K
so
V
1
V
0
=
T
1
T
0
=
473
K
373
K
=
1.27
(b) If the pressure is held constant, what is the volume if the Kelvin temperature is
doubled?
Here things are simple since
T
1
=
2
T
0
,
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V
1
V
0
=
T
1
T
0
=
2
T
0
T
0
=
2.0
Problem 16.20
A 20cmdiameter cylinder that is 40 cm long contains 50 g of oxygen gas at 20
degree(s)C.
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 Spring '08
 BEANE
 Physics, Mass, number density

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