The vapor pressure of dichloromethane, CH2CL2 at 0 degrees C is 134 mmHg. The normal boiling point of dichloromethane is 40 degrees C. Calculate its molar heat of vaporization.
I tried using the The Clausius-Clapeyron equation but no luck.
**Thanks to anyone who helps**
- schmisoLv 71 decade agoFavorite Answer
Clausius Clapeyron equation is the right idea.
You have two temperatures with their vapor pressures
T₁ = 0°C = 273 K with p₁ = 134 mmHg
and the normal boiling point
T₂ = 40°C = 313K with p₂= 1atm = 760mmHg
Solve the Clausius for the heat of vaporization and use the values above:
ln(p₂ / p₁) = (ΔHv / R ) · (1/T₁ - 1/T₂)
ΔHv = R · ln(p₂ / p₁) / (1/T₁ - 1/T₂)
= 8.314J/molK · ln(760mmHg / 134mmHg) / (1/273K - 1/313K)
= 30823J/mol = 30.8kJ
This value is a bit greater than reported values (NIST webbook) are between 28kJ/mol and 29kJ/mol. So the calculated value is not perfect but o.k. to my mind.
- 4 years ago