>>12841714To my understanding, looking at the Wikipedia page, it appears that initially you dissolve SO3 in H2O. You get some H2SO4 however it is not particularly concentrated and therefore you pump more SO3 into it until you achieve 97% concentration of aqueous H2SO4. Again, importantly, such a reaction must be performed in a sealed vessel/flask as you want nearly all of your H2O molecules to react with SO3, but SO3 is volatile. Basically one can only assume this takes place in a highly pressurised system. This renders it completely impractical if done without the equipment which is typically industrially available.
