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They are the primary intermolecular attractive forces that act between nonpolar molecules. -Apex.
They are named after Johannes Diderik van der Waals who was the first to postulate about inter molecular forces
Van der Waals interactions result when electrons are not symmetrically distributed in a molecule
you don't solve for a, a is a value that's given in a table... you just find it in your text book or somethng, it gives you the value of a for the specific real gas you're working with.