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Chemistry Forums for Students => Physical Chemistry Forum => Topic started by: apollobyter on April 10, 2005, 07:21:10 PM

Title: Enthalphy of vaporization
Post by: apollobyter on April 10, 2005, 07:21:10 PM

Hi

Can anyone tell me how you can calculate/estimate the enthaply of vaporization of a molecule knowing ONLY it's boiling point (and its molecular mass)?

I cannot calcuate this value without knowing other parameters (eg vapour perssure). Could someone please tell me if this is possible and how it is done?

thank you

Title: Re:Enthalphy of vaporization
Post by: eugenedakin on April 18, 2005, 01:11:57 AM

Hello Apollobyter,

Enthalpy of vaporization of a molecule can be calculated when a chemical reaction occurs.  Here is an example:
(CH3-H) + (Cl-Cl) --> (CH3-Cl) + (H-Cl)
(H=104) + (H=58) ---> (H=83.5) + (H=103)

DeltaH = (104+58)-(83.5+103) => -24.5 KCal/mole

Knowing the molecular mass, you can now calculate the KiloCalories.

I hope this helps,

Eugene Dakin Ph.D., P.Chem.