Calculate the vapor pressure of methanol at 40.0°C from the data given below:
Enthalpy of vaporization (∆H_vap= 35.2 kJ/mol;boiling point = 64.6°C;
Vapor pressure at 64.6°C = 760 torr)

Question

Quizplus · Accepted Answer

We can use the Clausius-Clapeyron equation to calculate the vapor pressure of methanol at 40.0°C.
ln(P1/P2) = (∆Hvap/R)((1/T2) - (1/T1))
Plugging in the values:
ln(P1/760) = (35.2 kJ/mol / 8.314 J/mol K) ((1/313.15 K) - (1/337.75 K))
Simplifying:
ln(P1/760) = -3.849
P1/760 = e^(-3.849)
P1 = 283 torr (rounded to three significant figures)

Calculate the Vapor Pressure of Methanol at 40