How is the boiling point relate to vapor pressure?

1 Answer
anor277
Jun 11, 2018

An old question....and an old problem....

Explanation:

The boiling point of a liquid are those conditions of temperature and pressure, when the VAPOUR pressure of a liquid is equal to the ambient pressure, and bubbles of vapour form directly in the liquid. The "normal boiling point" is specified when the AMBIENT pressure, and ALSO the vapour pressure of the BOILING LIQUID is "ONE ATMOSPHERE".

And this underlies the principle of vacuum distillation. A vacuum pump can SUBSTANTIALLY reduce the ambient pressure...and at an accessible temperature, the vapour pressure of the liquid may be 1*mm*Hg or even lower...and so the liquid comes across...

AS a first approx. we can sometimes use a vapour pressure nomograph to approximate the boiling point of a liquid AT REDUCED pressure...

picstopin.compicstopin.com

I know there is such a nomograph on the front of the "Chemists Companion"...and also instructions on how to use it....

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