>So why the two words then?<

Answering this from a purely linguistic point of view, and apolgies to wsieber for appearing to spurn all your chemical expertise, but I'm not doing really, believe me!)

why not?

A huge/enormous/gigantic/immense number/quantity/amount of English words can substitute for/replace each other without loss/reduction of understanding/comprehension.

Isn't that the underlying and wonderful delight of language?