I tried to calculate heat of reaction of Claus reaction. Using this reaction 2H2S + SO2 ===> 3S + 2H2O, the reaction is endothermic instead of what should be, which is exothermic. Does anyone know what's wrong with that?
The Claus reaction includes partial (1/3) oxidation of H2S to SO2 i/o to enable the reaction you mentioned. The reaction you mentioned is exothermic [Δ]Ho298= -147 kJ/mol.
For the chemistry and thermodynamics of the Claus process see: