Re: Please explain how acetone causes the molecular breakdown of styrofoam?

There is an old adage in chemistry:  "like dissolves like".

Styrofoam is polystyrene that has been puffed up with a gas into a 
foamy material that hardens.  Much of it is gas trapped in bubbles,
which is why it is so light.

Polystyrene itself is a hydrocarbon, which means it is made up only
of carbon and hydrogen atoms bound together.  Since "like dissolves
like," a hydrocarbon would be likely to dissolve this substance.
Acetone is a hydrocarbon and polystyrene dissolves in it.

So if enough acetone is used, all of the styrofoam will be dissolved.

Basically, it's like putting a spoonful of sugar into a cup of hot water
- you stir the mixture and the sugar molecules in solid form is dissolved
by the hot water.

Another interesting point is that in the history of chemistry, there was
a great search for a universal solvent (as water is sometimes referred to)
- in other words, a liquid which would dissolve all other materials.
But the search was stopped when someone realized that if such a liquid
existed, there would exist no material with which to make a container.