The vapor pressure of a liquid at a given temperature lower than its boiling point can be calculated if the boiling point and entropy of vaporization are known.
vapor pressure in mm Hg at given temperature in °C =
= 760 * 10 ^ ((-1) * A / B)
A =
= (entropy of vaporization at 760 mm Hg) * ((boiling temperature in °C) - (given temperature in °C))
B =
= (273.1 + (given temperature in °C)) - (0.15 * ((boiling temperature in °C) - (given temperature in °C)))
where:
• The entropy of vaporization for the liquid can be estimated as in the immediately preceding section.
• 273.1 + (given temperature in °C) = the absolute temperature in °K
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