Intermolecular forces
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Is it only solid carbon dioxide that has van der Waals forces, or is it even gaseous CO2? If only solid, why?
Corrie writes ...
van der Waals' forces are always present between carbon dioxide molecules but they are very distance dependent. They are only significant over very short distances, when the molecules are very close or in contact.
Whether a substance is a solid, liquid or gas under given conditions of pressure and temperature is a result of a balance betweeen the strength of the intermolecular forces pulling them together and their own energy of movement - their kinetic energy - driving them apart.
In solid carbon dioxide the low temperature means that the intermolecular forces can overcome the tendency of the molecules to move about and hold them in position in the solid lattice.
In gaseous carbon dioxide the molecules have enough energy to overcome the intermolecular forces of attraction when two molecules get close or collide.
I know some textbooks give the impression that in a gas the intermolecular forces are non-existent. If that was the case the gas would never condense to a liquid when it was cooled.
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updated: 02 April 2007
