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Homework Statement
Vapour pressures of a liquid have been measured and fit to the following equation:
Log10 P (mmHg) = -3571/T + 8.999
The melting point has been determined to be 392.7 K.
A Cp value given for the liquid is 250 J/mol K
and the ΔSvap is 117.20 J/mol K
Homework Equations
Clausius Clapeyron:
ln(P1/P2)= ΔH/R*(1/T2 - 1/T1)
The Attempt at a Solution
T1= 392.7 K P1 = 0.8045 mmHg (from the equation, giving the vapour pressure of the LIQUID at the melting point).
T2= 298.15 K P2= 1.052E-3 mmHg
From the Clausius Clapeyron:
ln(0.8045 mmHg/1.052E-3 mmHg)= ΔH/R*(1/298.15 K - 1/392.7 K)
ΔH/R = 8221.89 K-1
ΔH = 68361 J/mol
ΔH/T = ΔS = 68361/298.15 = 229.29 J/mol K
However the answer is 350.60 J/mol K.
I tried adding the ΔSvap to the derived value (229.29+117.2) , however that only gives me 346.5 J/mol K