A certain liquid has a vapor pressure of 92.0 Torr at 23.0 ∘C and 274.0 Torr at 45.0 ∘C.

Question

Calculate the value of Δ𝐻∘vap for this liquid.

Δ𝐻∘vap=____ kJ/mol

Calculate the normal boiling point of this liquid.

boiling point:____ ∘C

Answer 1

Clausius Clapeyron equation:

ln(P2/P1) = -∆Hvap/R (1/T2 - 1/T1)

P1 = 92.0 torr

P2 = 274 torr

T1 = 23 + 273 = 300K

T2 = 45 + 273 = 318K

∆Hvap = ?

R = 8.314 J/Kmol = 0.008314 kJ/Kmol

ln (274/92) = -∆Hvap / 0.008314 (1/318 - 1/300)

1.09 = -∆Hvap / 0.008314 (0.00314 - 0.00333)

1.09 = 0.000185 ∆Hvap / 0.008314

∆Hvap = 49.0 kJ/mol

To find the normal boiling point, repeat the above calculations using this ∆Hvap and P2 = 760 torr (standard) and solve for T2.