Question

the vapor pressure of SiCL4 is 100 mmHG at 5.4 C and the normal boiling point is 57.65 C a. calculate Hvap (in kj/mol) for SiCL4. b. determine the vapor pressure (in mmHg) of SiCL4 at 30 C

Answer 1

Here we use Clausius-Clapeyron relation:
ln(P2/P1) = (DH/R)*(1/T1-1/T2)
Where DH is Hvap

ln(P2/P1) = (Hvap / R)(1 / T1 - 1 / T2)
ln(P2/100 mm Hg) = [Hvap / (8.314 J/mol-K)][1 / (5.4 + 273 K) - 1 / (57.65 + 273 K)]
Where P1=100, P2=760, T1=278.4, and T2=330.65.
Hvap = R*ln(P2/P1)/(1/T1-1/T2)
= 8.314*ln(760/100)/(1/278.6-1/330.65)
= 29.84 (kJ/mol)

b)ln(P2/P1) = (?Hvap/R) (1/T1 - 1/T2)

ln(P2/100) = (29.84 x 10^3 / 8.314) (1/278.4 - 1/ 302)

ln(P2/100)= 1.007

P2=2.74*100

=> P2 = 274 mm Hg