Vapour pressure of water
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Vapour pressure of water can be used in many experiments, particularly experiments relating to gases. A common classroom experiment in which the vapour pressure at various temperatures table is used is when trying to find the molar mass of butane. The experiment is done by releasing butane gas from a cigarette lighter underwater into glass tubing. By calculating the partial pressure of the gas and subtracting the atmospheric pressure on the day that the experiment was conducted, it is possible to obtain an accurate result. This can be done with other gases with the same process.
Some equations used to approximate the vapor pressure of water are (in order of increasing accuracy):
A very simple equation:
-
- P = exp(20.386 − 5132 / T)
- where P is the vapour pressure (mmHg) and T is the temperature in Kelvin
Using this Antoine equation (for the range from 60 to 150 °C):
- or transformed into this temperature-explicit form:
- where the temperature T is in degrees Celsius and the vapour pressure P is in mmHg.
[edit] Vapor pressure of water at various temperatures
- See Water (molecule) for the referenced table of data that appears below, under subtitle "Vapor Pressures of Water".
Temperature
(°C) Pressure
(torr) Pressure
(mbar)
(°C) Pressure
(torr) Pressure
(mbar)
0 4.58 6.11
5 6.54 8.72
10 9.21 12.28
12 10.52 14.03
14 11.99 15.99
16 13.63 18.17
17 14.53 19.37
18 15.48 20.64
19 16.48 21.97
20 17.54 23.38
21 18.65 24.86
22 19.83 26.44
23 21.07 28.09
24 22.38 29.84
25 23.76 31.68
[edit] See also
[edit] References
Garnett, Pat; Anderton, John D; Garnett, Pamela J (1997) Chemistry Laboratory Manual For Senior Secondary School. Longman. ISBN 0582867649.
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