Chemistry Reference
In-Depth Information
Be careful; this is the number of moles of gas, not the
number of moles of HgO! We must determine the number of
moles of HgO from the balanced chemical equation.
O
2
a
1 mol Cl
2
70.9 g Cl
2
(b)
0.901 g Cl
2
b
0.0127
1
mol Cl
2
(0.0127
1
mol) (0.0821 L
#
atm/mol
#
K) (298 K)
12.4 L
nRT
V
2 HgO(s) £ 2 Hg(
/
)
O
2
(g)
P
a
2 mol HgO
1 mol O
2
0.0251 atm
0.0930 mol O
2
b
0.186 mol HgO
(c)
Equal numbers of grams of
N
2
and
Cl
2
are different
Heat
numbers of moles.
12.90
2 NaHCO
3
(s)
¡
Na
2
CO
3
(s)
CO
2
(g)
H
2
O(g)
(1.10 atm) (5.52 L)
(0.0821 L
#
atm/mol
#
K) (285 K)
0.259
5
mol
PV
RT
a
1 mol NaHCO
3
84.0 g NaHCO
3
1 mol CO
2
2 mol NaHCO
3
12.75
n
14.2 g NaHCO
3
b
a
b
0.0845
2
mol CO
2
11.4 g
0.259
5
mol
43.9 g/mol
(0.0845
2
mol) (0.0821 L
#
atm/mol
#
K) (298 K)
1.00 atm
nRT
P
V
1 atm
760 torr
12.79
682 torr
a
b
0.897
4
atm
2.07 L
12.93
(a)
5 O
2
(g)
4 NH
3
(g) £ 4 NO(g)
6 H
2
O(
/
)
PV
RT
(0.897
4
atm) (1.55 L)
(0.0821 L
#
atm/mol
#
K) (298 K)
n
(5.00 mol O
2
) (0.0821 L
#
atm/mol
#
K) (273 K)
1.00 atm
(b)
112 L
0.0568
5
mol
1.60 g
(4.00 mol NH
3
) (0.0821 L
#
atm/mol
#
K) (273 K)
1.00 atm
0.0568
5
mol
28.1 g/mol
89.7 L
The empirical formula is calculated as in Section 7.4:
(4.00 mol NO) (0.0821 L
#
atm/mol
#
K) (273 K)
1.00 atm
89.7 L
a
1 mol C
12.01 g C
85.63 g C
b
7.130 mol C
(c)
The ratios of part (b) and of the balanced chemical equa-
tion are both 5 : 4 : 4.
a
1 mol H
1.008 g H
14.37 g H
b
14.26 mol H
12.96
2 L SO
2
: 1 L O
2
: 2 L SO
3
14.26 mol H
7.130 mol C
2 mol H
1 mol C
12.98
For each gas, Because the two volumes are the
same, the two temperatures are the same, and the two pres-
sures are the same (and
R
is always the same), the numbers
of moles must be the same and therefore the numbers of
molecules must be the same.
PV
nRT
.
The empirical formula is The empirical formula mass
is therefore 14.0 amu per empirical formula unit. The num-
ber of empirical formula units per molecule is given by
CH
2
.
1 L
1000 mL
28.1 amu/molecule
14.0 amu/empirical formula unit
12.99
18.8 mL
a
b
0.0188 L
2 empirical formula units
1 molecule
a
0.0188 L
30.6 L
b
100%
0.0614%
The molecular formula is
(CH
2
)
2
,
or
C
2
H
4
.
The molecules themselves occupy less than 0.10% of the
volume of the gas, in accord with the kinetic molecular
theory.
12.101
The more moles of the gas present, the more molecules bom-
bard the walls and, therefore, the greater the force and pres-
sure, all other factors being equal.
12.81
The gas laws apply to moles of
molecules,
whether the mole-
cules are monatomic, diatomic, or polyatomic. In any case, the
correct number of atoms per molecule is necessary to calculate
masses of gaseous elements from the numbers of their moles.
(0.989 atm) (0.912 L)
(0.0821 L
#
atm/mol
#
K) (385 K)
PV
RT
12.82
n
(0.950 atm) (4.38 L)
(0.0821 L
#
atm/mol
#
K) (298 K)
PV
RT
12.103
n
0.170 mol
0.0285
4
mol H
2
O(g)
5.43 g
0.170 mol
31.9 g/mol
2 H
2
(g)
O
2
(g) £ 2 H
2
O(g)
MM
a
2 mol H
2
2 mol H
2
O
a
2.016 g H
2
1 mol H
2
0.0285
4
mol H
2
O
b
b
0.0575 g H
2
The gas is
12.105 (a)
At constant pressure, the volume of a gas is proportional
to its absolute temperature (Charles' law). After the vol-
ume increases with temperature, it can be brought back
to the original volume by increasing the pressure
(Boyle's law) by the same factor. Thus, at constant vol-
ume, the pressure is directly proportional to the absolute
temperature. For example, if we heat a gas to double its
original absolute temperature at constant pressure, the
volume will double. Then doubling the pressure will
halve the volume to its original value. The gas is now at
double the absolute temperature and double the original
pressure at the original volume. Thus, the pressure is
directly proportional to the absolute temperature at
constant volume.
O
2
.
(1.11 atm) (4.04 L)
(0.0821 L
#
atm/mol
#
K) (300 K)
0.182
1
mol
PV
RT
12.84
n
Be careful; this is the number of moles of gas, not the
number of moles of aluminum! We must determine the
number of moles of aluminum from the balanced chemical
equation.
H
2
2 Al(s)
6 HCl(aq) £ 2 AlCl
3
(aq)
3 H
2
(g)
a
2 mol Al
3 mol H
2
0.182
1
mol H
2
b
0.121 mol Al
PV
RT
(1.00 atm) (2.26 L)
(0.0821 L
#
atm/mol
#
K) (296 K)
0.0930 mol
12.87
n
