How to tell what intermolecular force is involved based on the boiling point and compound?

E.g. Compound: CH_3F
Boiling Point: -78.62

1 Answer
Jun 22, 2017

Answer:

Well, boiling point is a pretty good indicator of the extent of intermolecular force..........

Explanation:

When something boils we interrogate the equilibrium........

#"Stuff(l) "rightleftharpoons" Stuff(g)"#

In the liquid state, the stuff exerts a #"vapour pressure"#, which is a function of temperature. When the liquid exerts a vapour pressure that is EQUAL to the ambient pressure, boiling occurs, and bubbles of vapour form directly in the liquid.

The #"normal boiling point"# is specified when the vapour pressure of the liquid is equal to #"ONE ATMOSPHERE"#.

To draw your attention to a practical examples, we know that the #"normal boiling point"# of water is #100# #""^@C#; i.e. at #100# #""^@C#, water has a vapour pressure of #1*atm#. At lower temperatures water exerts an equilibrium vapour pressure, which are extensively tabulated, and which often we must take into account when we (say) collect a volume of gas by displacement of water.

In you example, you quote #H_3CF# with a boiling point of #-78.6# #""^@C#, versus, say, #CH_4# with a boiling point of #-164.0# #""^@C#, versus, say, #CH_2F_2# with a boiling point of #-52.0# #""^@C#. In this series, dipole-dipole interaction is probably the dominant intermolecular force.