Question

At 50.14k a substance has a vapor pressure of 258.9 torr. calculate its heat of vaporization in kj/mol if it has a vapor pressure of 277.5 torr at 161.2k

Answer 1

T₁ = 50,14 K.
p₁ = 258,9 torr.
T₂ = 161,2 K.
p₂ = 277,5 torr.
R = 8,314 J/K·mol.
Using Clausius-Clapeyron equation:
ln(p₁/p₂) = - ΔHvap/R · (1/T₁ - 1/T₂).
ln(258,9 torr/277,5 torr) = -ΔHvap/8,314 J/K·mol · (1/50,14 K - 1/161,2 K).
-0,069 = -ΔHvap/8,314 J/K·mol · (0,0199 1/K - 0,0062 1/K).
0,0137·ΔHvap = 0,573 J/mol.
ΔHvap = 41,82 J.