I found that $\ce{SO2 + 1/2 O2 -> SO3}$ when catalysed by platinum and heated to $\pu{700 ^\circ C}$. On the other hand I found that $\ce{SO3 -> SO2 + 1/2 O2}$ with same catalysator and temperature about $\pu{800 ^\circ C}$. How depends these two cases in real reaction? What controls which reaction will happen?
I thought that one reaction is exothermic and other endotermic, and duration of reaction and temperature controls which reaction happens. But facts I found are different. Sorry for maybe too simple question. I would be pleased with some tips which chapters of chemistry to study to understand my problem more deeply.