One process used to manufacture sulfuric acid is called the contact the amount of energy released when 1.00 mole of sulfur trioxide is produced

From the reaction; 

2SO2(g) + O2(g) = 2SO3(g)  + 394 kJ
   In the reaction a mixture of plantinum and vanadium (V) oxide may be used as a catalyst for the reaction. The sulfur trioxide produced is then used to make sulfuric acid.
 The energy that is required to release 1 mole of sulfur trioxide is +394 joules 
For one mole of sulfur trioxide; 
the energy that will be released will be 394/2 = 197 kJ
Thus; the amount of energy released is +197 kJ