# Chemistry- Clausius Clapeyron Equation?

The heat of vaporization of water is 40.67 kJ/mol. What is the vapor pressure of water (in atm) at 25oC?

note: I THINK i did it. I got this crazy large number and I have no idea if I did it correctly.

### 1 Answer

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- hcbiochemLv 71 month ago
The vapor pressure at 25 C should be much less than the vapor pressure at the boiling point, so perhaps you did something wrong

ln (p2/p1) = Delta Hvap/R (1/T1-1/T2)

You know that at 100 C( 373.15 K) the vapor pressure of water is 760 mm Hg. Using that as one point,

ln (p2/760) = (4.067X10^4 J/molK / 8.314 J/mol) (1/373.15 - 1/298.15)

p2 = 28.1 mm Hg

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I set it up right. But, I didn't get that answer. I calculated the right side--> -3.3006 and then I took the inverse of the natural log, which came to .0368 . I divided that, so 760 mmHg/.0368 and I got 20617.97. I think i did something wrong.