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The boiling point of water is the temperature at which the saturated vapor pressure equals the ambient pressure. Water supercooled below its normal freezing point has a higher vapor pressure than that of ice at the same temperature and is, thus, unstable. Calculations of the (saturation) vapor pressure of water are commonly used in meteorology.
The following table lists the Van der Waals constants (from the Van der Waals equation) for a number of common gases and volatile liquids. [ 1 ] To convert from L 2 b a r / m o l 2 {\displaystyle \mathrm {L^{2}bar/mol^{2}} } to L 2 k P a / m o l 2 {\displaystyle \mathrm {L^{2}kPa/mol^{2}} } , multiply by 100.
This is illustrated in the vapor pressure chart (see right) that shows graphs of the vapor pressures versus temperatures for a variety of liquids. [7] At the normal boiling point of a liquid, the vapor pressure is equal to the standard atmospheric pressure defined as 1 atmosphere, [1] 760 Torr, 101.325 kPa, or 14.69595 psi.
1 atm = 1 013 mbar or hPa; 1 mbar or hPa = 0.7502467 mmHg; 1 pascal = 1 Newton per square metre (SI unit) 1 hectopascal is 100 pascals ... Water is coloured with ...
The table values for −100 °C to 100 °C were computed by the following formulas, where T is in kelvins and vapor pressures, P w and P i, are in pascals. Over liquid water. log e (P w) = −6094.4642 T −1 + 21.1249952 − 2.724552×10 −2 T + 1.6853396×10 −5 T 2 + 2.4575506 log e (T)
However, its empirical value remains important: the unique combination of pressure and temperature at which liquid water, solid ice, and water vapor coexist in a stable equilibrium is approximately 273.16 ± 0.0001 K [4] and a vapor pressure of 611.657 pascals (6.11657 mbar; 0.00603659 atm). [5] [6]
where p is the vapor pressure, T is temperature (in °C or in K according to the value of C) and A, B and C are component-specific constants. The simplified form with C set to zero: = is the August equation, after the German physicist Ernst Ferdinand August (1795–1870). The August equation describes a linear relation between the logarithm ...
e * is the saturation water vapor pressure T is the absolute air temperature in kelvins T st is the steam-point (i.e. boiling point at 1 atm.) temperature (373.15 K) e * st is e * at the steam-point pressure (1 atm = 1013.25 hPa) Similarly, the correlation for the saturation water vapor pressure over ice is: