Benzene has a heat of vaporization of 30.72kJmol−1 and a normal boiling point of 80.1 ∘C.
At what temperature does benzene boil when the external pressure is 599 mbar ?
Solution :
Use the Clausius-Clapeyron Equation
ln (P2 /P1) = -deltaHvap / R * (1/T2 -1/T1)
deltaHvap = 30.72kJ/mol
T1 = 80.1 +273 = 353.1K
T2 = need to find out
P1 = is the presssure normal boiling point = 1atm
P2 =599 mbar = 0.59atm ( as 1 atm = 1013mbar)
R = 8.314*10-3 kJ/K*mol
ln ( 0.59atm /1atm) = - 30.72kJ/mol / 8.314*10-3 kJ/K*mol ( 1/T2-1/353.1K)
-0.53 = -3695( 1/T2- 0.00283)
-0.53 /-3695 =( 1/T2- 0.00283)
1.43*10-4 = 1/T2- 0.00283
1/T2 = 1.43*10-4 +0.00283
1/T2 = 2.97*10-3
T2 = 336K
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