Environmental Engineering Reference
In-Depth Information
9
A
B
7
5
3
1
-1
0 0 0 0 0 0
Temperature (
0
C)
0
2
4
6
8
10
CaCl (% by weight)
FIGURE 2.4
Comparison of density change caused by temperature (A) and by increasing
concentration of calcium chloride (B). A 10 g liter
1
increase in CaCl concentration can be
offset by an approximately 50°C temperature increase. Seawater has an approximate salinity
of 3.5%; saline lakes can exceed this value many times (data from Dean, 1985).
in water tends to decrease when temperature increases (see Fig. 11.8). This
effect of temperature on gas solubility can have significant biological con-
sequences; fish are more likely to die of low oxygen stress when water tem-
peratures are elevated because less dissolved oxygen is held in warm water
and the fish's metabolic requirements for oxygen are increased as temper-
ature increases.
Additional properties of water include high heat capacity, heat of fu-
sion (freezing), heat of vaporization, and surface tension. Water has a high
heat capacity,
that is, it takes a relatively large amount of energy to in-
crease the temperature of liquid water. To illustrate, the specific heat ca-
pacities (in calories required to change the temperature of 1 g of a sub-
stance by 1 °C) are 1, 0.581, and 0.212 for water, ethanol, and aluminum,
respectively. Similarly,
heat of fusion
and
vaporization
are high for water
compared to other liquids (Table 2.2). A high heat capacity and heat of fu-
sion means that a considerable amount of solar energy is required to heat
TABLE 2.2
Heats of Fusion, Vaporizations, Heat Capacities, and Surface Tensions
of Various Liquids
a
Heat of fusion
Heat capacity at 25°C
Surface tension at 20°C
Viscosity
Heat of vaporization
(Cal g
1
)
(Cal g
1
°C
1
)
(dyn cm
1
)
(Cal g
1
)
Substance
(cp)
Water
79.7
1.00
73
1.00
539.6
Benzene
30.3
0.41
40
0.65
94.3
Mercury
2.8
0.03
435
1.55
67.8
Oxygen
3.3
—
—
—
50.9
a
Data from Keenan and Wood (1971) and Weast (1978).
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