Boiling Points and Pressure ```Name: Jordi Status: educator Age: 30s Location: N/A Country: N/A Date: Around 1999 ``` Question: I would like to know the different boiling points of water depending on the atmospheric pressure Replies: The boiling point of water is the temperature at which its vapor pressure equals the atmospheric pressure. So, what you need to know is the vapor pressure of water at different temperatures and then invert the information to get the temperatures corresponding to different vapor pressures. Extensive tables of vapor pressures of water have been prepared. I am not going to type in a table here; you can find the information in handbooks such as the CRC Handbook of Physics and Chemistry. Some sample numbers are: ```Temperature Vapor Pressure Vapor Pressure (C) (mm Hg) (fraction of 1 atm.) -10 2.149 0.28% 0 4.579 0.60% 10 9.209 1.21% 20 17.535 2.31% 30 31.824 4.19% 40 55.324 7.28% 50 92.51 12.17% 60 149.38 19.66% 70 233.7 30.75% 80 355.1 46.72% 90 525.76 69.18% 92 566.99 74.60% 94 610.9 80.38% 96 657.62 86.53% 98 707.27 93.06% 100 760 100.00% 110 1074.56 141.39% 120 1489 195.92% ``` To use a table like this, you need to know that standard atmospheric pressure is 760 mm Hg. You will notice that the temperature corresponding to this vapor pressure is 100 C, the boiling point of water. You will also notice from this table that nearly all of the action will be between 90 and 100 C. The boiling point of water will be 90 C when the pressure is 526 mm Hg, which is about 0.69 atmospheres. This is the air pressure at about 3000 meters above sea level, below which live almost all of the people in the world.Richard Barrans Jr., Ph.D. Chemical Separations Group Argonne National Laboratory You should be able to find this in the CRC Handbook of Chemistry and Physics. It will probably exist as a table of the vapor pressure of water at various temperatures. Water boils when the atmospheric pressure is equal to the vapor pressure for a given temperature. Bradburn Click here to return to the Chemistry Archives

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