Elle B.

asked • 11/17/20

Delta Hvap for water is 40.7 kJ/mol. Calculate the boiling point of water at 0.500 atm.

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Anthony T. answered • 11/17/20

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We can use the Clausius-Clapeyron equation to solve this. This equation is


ln(P1/P2) = ΔHvap/R (1/T2 - 1/T1) where R is the gas constant = 8.315 J mol-1 K-1


ln 1 atm /0.5 atm = 40700 J/mol/8.315 J/mol-K x (1/T2 K -1/373 K) Solve for T2.


0.693 = -13.41 + 5003//T2


14.1 = 5003/T2


T2 = 355 K or 82 C


Please check my math.

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J.R. S.

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Don't forget to change the units of R to match those of ∆H. So you should use 0.008314 kJ/Kmol.
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11/18/20

Anthony T.

I changed the delta H to Joules/mole first, so the units match. I made a mistake dividing deltaH by R. It should be 4895 rather than 5003, but the final result is about the same!
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11/18/20

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