Using your experimental value of Delta H_vap, calculate the vapor pressure of wa
ID: 475555 • Letter: U
Question
Using your experimental value of Delta H_vap, calculate the vapor pressure of water at 100 degree C, the boiling point of pure water at exactly 1 atmosphere of atmospheric pressure. The boiling point of a substance is defined as the temperature at which the vapor pressure of that substance in the liquid state is equal to the external atmospheric pressure. How does your calculated value of P_water at 100 degree C compare to the measured atmospheric pressure on the day of the experiment? Give an explanation for any discrepancy.Explanation / Answer
ln (P2 / P1) = Hvap / R [1/T1 - 1/T2]
T1 = 25oC = 298 K ; T2 = 373 K ;
find P1 using Antoine equation for water P1 = 108.07131-(1730.63)/233.426+25
P1 = 23.6864 mmHg = 0.031166 atm
ln (P2 / 0.031166) = 39.79*103 / 8.314 [1/298 - 1/373]
(P2 / 0.031166) = e3.22923
P2 = 25.26040*0.031166 = 0.78726 atm
Boiling point of pure water at 1 atm
P2 = 1atm ; P1 = 0.031166 ; T1 = 298 K
ln(1/0.031166) = 39.79*103 / 8.314 [1/298 - 1/T]
7.247174*10-4 = 1/298 - 1/T
T = 380.0854 K = 106.935oC
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