Chemistry Thermodynamics Math Question 3

Question

The boiling point of methanol is 64.7 C. Calculate the equilibrium vapor pressure of methanol at 32 C. The enthalpy of vaporization of methanol is 37 kJ/mol. (bar?)

Answer 1

Use the Clausius Clapeyron equation:

ln (P2/P1) = -∆Hvap/R (1/T2 - 1/T1) ... be sure to keep units of R and ∆H the same...

T1 = 64.7 + 273 = 337.7K

P1 = 1 bar

T2 = 32 + 273 = 305K

P2 = ?

R = 8.314 J/K-mol

∆Hvap = 37 kJ/mol = 37,000 J/mol

ln(P2/1) = -37,000/8.314 (1/305 - 1/337.7)

ln P2 = -4450 (0.00328 - 0.00296) = -1.424

P2 = 0.24 bar