Saturation (physics)

from Wikipedia, the free encyclopedia

In physics and chemistry , one speaks of saturation when a substance , body or field has absorbed such a large amount of another that further absorption under the given conditions would lead to an energetically less favorable state .

This less favorable state can spontaneously degrade in material systems such as solutions , melts or gases , especially if the helpful crystallization (so-called seed crystals ) or condensation nuclei are present . In the absence of this, however, this condition can persist as oversaturation for a longer period of time.

Saturation of liquids

If a substance is dissolved in a liquid , it is called a solvent and the resulting mixture is called a solution . The solubility of the substance in the solvent is decisive for the saturation . If the highest possible amount of the substance is dissolved, one speaks of a saturated solution and describes the corresponding concentration of the substance as the saturation amount or saturation concentration . This amount of saturation depends on the type of solvent and the temperature. It cannot be exceeded by adding more substances; the excess substance instead remains in the liquid as a separate phase (e.g. as a solid). It is still possible to exceed this limit, e.g. B. by lowering the temperature of a previously saturated solution. In this case one speaks of a supersaturated solution, see above.

Saturation of gases using the example of water vapor

Saturation diagram of water vapor

Water vapor is saturated when it is no longer able to further increase its own concentration in the air , as this already carries the maximum humidity with it. Terms that can be used synonymously for the saturation of the water vapor are:

Cooling the air below the dew point without condensation ( fog , cloud ) occurring, leads to oversaturation. The reason for this is the lack of condensation nuclei , i.e. aerosols such as dust or ice particles . However, since condensation nuclei are usually present, there is hardly any oversaturation of more than one percent in the earth's atmosphere . The table below contains some exemplary values ​​for the amount of saturation of water vapor as a function of temperature from D. Sonntag (1982). Due to the different values ​​of the saturation vapor pressure below a temperature of 0 ° C, a distinction must be made as to whether the surface is water or ice. The saturation amount or saturation concentration of the water vapor is also referred to as the maximum air humidity . This can be calculated with the following formulas:

Above water:

About ice:

The individual symbols stand for the following quantities :

Saturation values ​​of the absolute air humidity
Temperature in ° C Amount of saturation above water in g / m³ Amount of saturation over ice in g / m³
−100 4.5436 1.7465
−95 1.1432 4.5752
−90 2.7247 1.1373 ·
−85 6.1778 2.6939
−80 1.3378 6,1013
−75 2.7765 1.3260
−70 5.5406 2.7735
−65 0.010661 0.005598
−60 0.019832 0.010930
−55 0.035750 0.020692
−50 0.062584 0.038056
−45 0.10661 0.068124
−40 0.17702 0.11890
−35 0.28700 0.20265
−30 0.45501 0.33776
−25 0.70640 0.55127
−20 1.0753 0.88211
−15 1.6068 1.3854
−10 2.3596 2.1380
−5 3.4086 3.2449
−4 3.6619 3.5205
−3 3.9316 3.8172
−2 4.2187 4.1363
−1 4.5239 4.4794
0 4.84843 4.84795
1 5,19317 -
2 5.55921 -
3 5.94766 -
4th 6.35967 -
5 6,79642 -
6th 7.25917 -
7th 7.74919 -
8th 8.26783 -
9 8.81648 -
10 9.39658 -
11 10.0096 -
12 10.6572 -
13 11.3408 -
14th 12.0623 -
15th 12.8232 -
16 13.6254 -
17th 14.4707 -
18th 15.3611 -
19th 16.2984 -
20th 17.2848 -
21st 18.3224 -
22nd 19.4132 -
23 20.5596 -
24 21.7638 -
25th 23.0283 -
26th 24.3554 -
27 25.7477 -
28 27.2079 -
29 28.7385 -
30th 30.3424 -
35 39.5623 -
40 51.0726 -
45 65.3114 -
50 82.7730 -
55 104.011 -
60 129.642 -
65 160.344 -
70 196.863 -
75 240.011 -
80 290.669 -
85 349.782 -
90 418,369 -
95 497.511 -
100 588,359 -

In applications such as building physics , drying , meteorology , instead of saturating amount occurring in the above formulas mostly saturated vapor pressure as a measure of the maximum humidity used - see. Humidity measurements . The formulas are based on the general gas equation (see vapor pressure ).

Saturation of the magnetization of (ferro) magnetic substances

When magnetizing z. B. Iron saturation occurs when all elementary magnets are aligned within an iron core . In this case one speaks of saturation magnetization .

literature

D. Sonntag, D. Heinze: Saturation vapor pressure and saturation vapor density tables for water and ice . 1st edition, VEB German publishing house for basic industry, 1982