# Q & A: Clausius-Clapeyron boiling

Q:
Dear Sir/madam, Iam not clear with the Clausius Clapeyron equation to calculate the boiling point of liquid with high vaccum. the formula which I found is given below. please illustrate with the coulpe of examples based on the below mention formula.Awaiting for your reply. Clausius Clapeyron: ln (P2 / P1) = (Hvap / R)( (1/T1) - (1/T2) . In the equation, P1 is the vapor pressure at some known temperature and pressure -- such as atmospheric pressure -- and T1 is the corresponding temperature. P2 is the new pressure once vacuum is applied, R is a constant, and Hvap is the amount of heat energy needed to evaporate a given amount of the liquid.
- DINESH (age 22)
INDIA
A:
Let's say that you know the boiling point T1 when P1=1 atm. You probably can also look up the (approximately constant) latent heat, H, and of course have the universal gas constant, R.

With that standard background, I think what you're asking is  how to calculate the boiling point T2 for some very low pressure P2. Well, let's just solve for T2.

T2 = T1/ (1+(HT1/R*ln(1atm/P2))).

You can take it from there.

Mike W.

(published on 06/07/2011)

## Follow-Up #1: water boiling temperature vs. pressure

Q:
IS THERE ANY CALCULATION FOR BOILING POINT AGAINST VACUUM / NAGATIVE PRESSURE & PRESSURE
- snehal harishchandra patel (age 33)
surat
A:
Check the preceding answer (17269) and its follow up if you need more explanation.
Just type 17269 into the search box.

Mike W.

(published on 04/27/2012)