Chemistry Reference
In-Depth Information
individual pressures of the components of a gaseous mixture is equal to the total
pressure of the mixture:
Open to
atm
osph
ere
(One pressure,
P
i
,
for each gas
, i
)
p
Gas
mixture
P
total
P
1
P
2
P
n
The pressures of the individual components of a mixture are called
partial pres-
sures.
If the mixture is contained in a way that its pressure is equal to that of the
atmosphere (Figure 12.7), the total pressure is equal to the barometric pressure.
Mercury
level
EXAMPLE 12.17
A mixture of oxygen and neon contains oxygen at a pressure of 726 torr and
neon at a pressure of 44 torr. What is the pressure of the mixture?
Figure 12.7
Situation in
Which the Total Pressure of a
Mixture of Gases Equals
Barometric Pressure
Because the mercury levels are the
same, the pressure of the gas mixture
is equal to the pressure of the
atmosphere—barometric pressure.
Solution
P
total
P
Ne
P
O
2
44 torr
726 torr
770 torr
Practice Problem 12.17
A mixture of oxygen and neon has a baro-
metric pressure of 1.031 atm. If the pressure of the oxygen is 0.922 atm, what
is the pressure of the neon?
The ideal gas law applies to a mixture of gases as a whole and also to each
of its components. That is,
P
total
V
n
total
RT
and
P
i
V
n
i
RT
where
i
stands for any component of the mixture.
EXAMPLE 12.18
Calculate the total number of moles in a 10.5-L sample of gas at 292 K, con-
taining
O
2
at 0.622 atm and
N
2
at 0.517 atm. Also calculate the number of moles
of
O
2
present.
Solution
The total pressure of the gas mixture is
0.622 atm
0.517 atm
1.139 atm
The total number of moles is
(1.139 atm) (10.5 L)
(0.0821 L
#
atm/mol
#
K) (292 K)
n
total
0.499 mol
The number of moles of
O
2
is
(0.622 atm) (10.5 L)
(0.0821 L
#
atm/mol
#
K) (292 K)
n
O
2
0.272 mol O
2
