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Water vapor pressure chart

Vapor pressure of H2O at various temperatures (celsius)

Temp (C) Pressure (mm Hg)
-10 2.1
-5 3.2
0 4.6
5 6.5
10 7.0
15 9.2
20 17.5
22 19.8
25 23.8
30 31.8
35 42.2
40 55.3
50 92.5
60 149.4
70 233.7
80 355.1
90 525.8
95 633.9
100 760

Modified from Nebergall et. al 1976

Note that when water vapor pressure equals atmospheric pressure, then the water molecules are free to jump into the gas state. The pressure "up" cancels the pressure "down" and boiling begins.

To find a value not on the chart you must interpolate. This can introduce some error since water vapor pressure in not a straight line graph.

Example: Set up a proportionality and solve for X. Use the chart entry closest to the number you want. 32C  is closer to 30 than to 35 so

__30C                 =     __35C       

31.8mm Hg                        X

X = 37.1 mm Hg