107
Gases and the
Kinetic-Molecular
Theory
12
12-1
Pressure is a measure of a force applied per square unit of surface area. Pressure is the force per unit
area of a gas (or other fluid) confined to a container.
12-3
A mercury barometer consists of a glass tube, sealed at one end, filled with mercury, and then inverted
into a dish of mercury.
The mercury in the tube falls until the pressure due to its height matches the
pressure due to the air (the atmosphere) on the surface of the mercury in the dish. The height of the
mercury column is a measure of the external air pressure.
12-5
(a)
? mm Hg
=
675 torr
x
1 mm Hg
1 torr
=
675 mm Hg
(b)
? atm
=
675 torr
x
1 atm
760. torr
=
0.888 atm
(c)
? Pa
=
675 torr
x
1 atm
760. torr
x
1.013 x 10
5
Pa
1 atm
=
9.00 x 10
4
Pa
(d)
? kPa
=
9.00 x 10
4
Pa
x
1 kPa
1000 Pa
=
90.0 kPa
12-7
We use conversion factors based on the equivalences
1 atm
=
760 torr
=
101.3 kPa.
atm
torr
Pa
kPa
Standard atmosphere
1
760
1.013 x 10
5
101.3
Partial pressure of nitrogen in
the atmosphere
0.780
593
7.90 x 10
4
79.0
A tank of compressed hydrogen
1.59
1.21 x 10
3
1.61 x 10
5
1.61 x 10
2
Atmospheric pressure at the
summit of Mt. Everest
0.333
253
3.37 x 10
4
33.7
12-9
The height of liquid is inversely proportional to its density; the lower the density of the liquid, the
taller the column would be.
height of oil column
=
760. mm Hg x13.5 g/mL0.92 g/mLx1 m1000 mm= 11 m
12-11
31 psi
x
1 atm
14.70 psi
=
2.1 atm guage pressure
total pressure
= 1.0 atm + 2.1 atm =
3.1 atm

108
12-13
Yes, because for a given substance, the number of moles is directly proportional to the mass of
substance.
12-15
V = 2.50 L x
1.00 atm
2.50 atm
=
1.00 L
12-17
P
1
=
0.500 atm
V
1
=
75.0 mL
P
2
is given in each part
V
2
=
?
For each part, we use Boyle’s Law,
P
1
V
1
=
P
2
V
2
or
V
2
=
P
1
V
1
P
2
(a)V2= 0.500 atm x 75.0 mL5.00 atm= 7.50 mL(b)V2= 0.500 atm x 75.0 mL0.0500 atm= 7.50 x 102mL(c)V2= 0.500 atm x 75.0 mL555 torr x 1 atm760 torr(d)V2= 0.500 atm x 75.0 mL5.00 torr x 1 atm760 torr(e)V2= 0.500 atm x 75.0 mL5.5 x 10-2torr x 1 atm760 torr
=
51.4 mL
=
5.70 x 10
3
mL
=
5.2 x 10
5
mL
12-19
(a)
Yes.
From graphs analogous to A, B, or C in Figure 12-5, but with temperature expressed in
o
F,
we could find the value on the Fahrenheit scale to which the lines extrapolate.
This would provide
the constant that we could use to convert from the Fahrenheit to the “absolute Fahrenheit” scale.
(b)
Yes.
By the reasoning in part (a), it would not matter what size the degree was; the same
approach would still give an absolute scale.
12-21
K
o
C
o
F
Normal boiling point of water
373
100.
212.
Reference for thermodynamic data
298.15
25.00
77.00
Dry ice becomes a gas at atmospheric pressure
194.6
–78.5
–109.3
The center of the sun (estimated)
1.53 x 10
7
1.53 x 10
7
2.75 x 10
7
12-23
At approximately 25
o
C or 298 K, the volume is 20 mL.
At approximately 325
o
C or 598 K, the volume is 40 mL.