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Saturday, April 9, 2016

Organic Chemistry, "Function", Part 2 - Permanent Dipole Intermolecular Forces and Boiling Point

Greetings,

In my last post, the effect of increasing molecular weight on boiling point was explained.  There is also a similar trend for increasing Permanent Dipole Moment.  This trend can be seen by choosing compounds with similar molecular weights.  The following chart is an illustration of the effect.


The increase in boiling point for increasing intermolecular force makes sense when one considers what boiling actually is; A thermodynamic state occurring when the kinetic energy of a molecule as part of a liquid becomes greater than the total intermolecular force the molecule has with neighboring molecules.  As the total intermolecular force increases, more energy is required to expel a molecule from the liquid surface, which is the interface between the liquid and gas states.  More energy required translates to a higher temperature required.  When boiling happens individual molecules can no longer be "held" in the liquid state and the substance transitions to the gas phase.  In essence, the compound assumes a pressure equal to the atmospheric pressure outside the container holding the liquid.

As always, thank you for reading!

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