Production of sulfuric acid

LURCH

I was recently reading about the method by which sulfuric acid was produced in the old days. Apparently, copper sulfate pentahydrate (green vitriol), when heated up, breaks down into copper dioxide, water, and sulfur trioxide. The sulfur trioxide and water then bond to form sulfuric acid. Now, I'm really weak on chemistry, but by looking at the chemical signatures of these substances it appears that an oxygen molecule is missing. Does this method give off oxygen as a byproduct?

Also, can the process be reversed? Can copper dioxide and sulfuric acid be combined to form green vitriol?

quetzalcoatl9

what is missing?

[tex]SO_3(g) + H_2O(l) \longrightarrow H_2SO_4(l)[/tex]

where are we missing oxygen?