Chemistry Reference
In-Depth Information
14.31
Nothing. No net quantity of water vaporizes, and no net
quantity of steam condenses.
(b)
The mass of the hot water is twice that of the cold water:
t
f
t
cold
2(
t
f
t
hot
)
14.32
No; the pressure will be equal to the vapor pressure if the liq-
uid and vapor phases are both present at equilibrium, but if
all the liquid is vaporized, the pressure may be below the va-
por pressure of water at that temperature.
3
t
f
100.0°C
20.0°C
t
f
40.0°C
The final temperature is merely the
weighted
average of the
original temperatures.
14.33
(a)
Heat
mc
¢
t
(35.0 g) (4.184 J/g
#
°C) (41.6°C
10.5°C)
14.52
(a)
(b)
(c)
(d)
(e)
H
2
O(s) £ H
2
O(g)
4550 J
4.55 kJ
2
O
2
(g) £ CO(g)
C(s)
(b)
Heat
mc
¢
t
C(s)
O
2
(g) £ CO
2
(g)
(35.0 g) (4.184 J/g
#
°C) (10.5°C
41.6°C)
C(s)
O
2
(g) £ CO
2
(g)
4550 J
4.55 kJ
(c) and (d)
In part (b), 4.55 kJ of heat must be
removed
from the
water.
14.54
(a)
(b)
8 C(s)
9 H
2
(g) £ C
8
H
18
(
/
)
2
2
O
2
(g) £ 8 CO
2
(g)
9 H
2
O(
/
)
C
8
H
18
(
/
)
0.442 J/g
#
°C.
14.35
The specific heat of iron, listed in Table 14.4, is
The change in temperature is given by
14.56
(a)
CH
2
O(
/
)
O
2
(g)£CO
2
(g)
H
2
O(
/
)
¢
H
561 kJ
heat
mc
127 J
(51.5 g) (0.442 J/g
#
°C)
5.57
9
°C
¢
t
(b)
¢
H
¢
H
f
(CO
2
)
¢
H
f
(H
2
O)
¢
H
f
(CH
2
O)
561 kJ
(
393 kJ)
(
286 kJ)
¢
H
f
(CH
2
O)
The initial temperature was
23.0°C,
and the change in
¢
H
f
118 kJ
temperature is
5.57
9
°C,
so the final temperature is
23.0°C
5.57
9
°C
28.6°C.
a
1 mol CH
2
O
30.0 g CH
2
O
118 kJ
1 mol CH
2
O
(c)
68.3 g CH
2
O
b
a
b
14.36
The total heat added to the metal and water is zero. Thus,
269 kJ
0
(46.0 g) (
c
metal
) (36.1°C
78.0°C)
(32.0 g) (4.184 J/g
#
°C) (36.1°C
23.1°C)
14.57
The last two equations represent the reverse of the formation
reactions of
0.903 J/g
#
°C
H
2
O
and
CO
2
,
respectively. For the first reaction:
c
metal
¢
H
¢
H
f
(products)
¢
H
f
(reactants)
The metal is most likely aluminum.
561 kJ
(
393 kJ)
(
286 kJ)
¢
H
f
(CH
2
O)
0.442 J/g
#
°C.
14.37
The specific heat of iron, listed in Table 14.4, is
The heat required is given by
¢
H
f
(CH
2
O)
118 kJ
(23.9 g) (0.442 J/g
#
°C) (41.7°C)
Alternatively, the three equations could be added, along with
their
Heat
mc
¢
t
441 J
¢
H
values, to give
14.42
(
m
water
)(
c
water
)(
t
f
t
water
)
m
Cr
c
Cr
(
t
f
t
Cr
)
0
2
O
2
CH
2
O £ C
H
2
¢
H
118 kJ
(215 g) (4.184 J/g
#
°C) (
t
f
19.0°C)
This is the reverse of the formation reaction for
CH
2
O,
so
(25.0 g) (0.45 J/g
#
°C) (
t
f
54.5°C)
0
¢
H
f
118 kJ
899.
6t
f
17,0
9
0
11.
3t
f
61
3
0
2
O
2
(g) £ CO
2
(g)
14.59
CO(g)
910.
9t
f
17,7
0
0
For 1 mol of CO:
t
f
19.4°C
¢
H
(
393.5 kJ)
(
110.5 kJ)
283.0 kJ
14.48
Heat
mc
¢
t
For 125 g of CO:
(250.0 g) (4.184 J/g
#
°C) (
¢
t
)
395
0
J
a
1 mol CO
28.0 g CO
283.0 kJ
1 mol CO
125 g CO
b
a
b
1260 kJ
¢
t
3.78°C
14.49
The heat is calculated in three steps: (a) warming the ice to
(b) melting the ice, and (c) heating the liquid water. The
answer is (d), the sum of these three:
(a)
Heat
mc
t
(27.7 g) (2.09 J/g·
C) (15.9
C)
920.
5
J
(b)
(c)
Heat
mc
t
(27.7 g) (4.184 J/g·
C) (25.0
C)
289
7
J
(d)
Heat
920.
5
J
928
0
J
289
7
J
13,10
0
J
13.10 kJ
14.60
(a)
16.0 kJ
(the sum of the two given equations)
0°C,
27.0 kJ
(b)
(the reverse of the first equation)
54.0 kJ
(c)
(double the answer in part [b])
Heat
m
¢
H
fusion
(27.7 g) (335 J/g)
928
0
J
C
12
H
22
O
11
(s)
12 O
2
(g) £ 12 CO
2
(g)
11 H
2
O(
/
)
14.61
¢
H
5648 kJ
C
6
H
12
O
6
(s)
6 O
2
(g) £ 6 CO
2
(g)
6 H
2
O(
/
)
14.51
Heat
0
(
m
cold
)(
c
cold
)(
t
f
t
cold
)
¢
H
2816 kJ
(
m
hot
)(
c
hot
)(
t
f
t
hot
)
C
6
H
12
O
6
(s)
6 O
2
(g) £ 6 CO
2
(g)
6 H
2
O(
/
)
(a)
Since the masses are equal and the specific heat is the
same, this equation reduces to
¢
H
2824
kJ
Subtracting the second and third of these equations from the
first yields:
t
f
t
cold
t
f
t
hot
2
t
f
50.0°C
20.0°C
C
12
H
22
O
11
(s)
H
2
O(
/
) £ C
6
H
12
O
6
(s)
C
6
H
12
O
6
(s)
¢
H
8 kJ
t
f
35.0°C
The final temperature is merely the average of the original
temperatures.
14.63
The second equation. The
complete
combustion (to give
by definition has associated with it
¢
H
comb
.
CO
2
)
