Vapor Pressure??

Question

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**

Answer 1

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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.

Source(s): http://en.wikipedia.org/wiki/Clausius-Clapeyron_eq...

Answer 2

30.9 kJ/mol