Question

Hey guys plz explain, why ∆H is negative here.

Answer 1

The ∆H is negative here because it is an exothermic reaction .

i) S(Rombic) on reaction with oxygen gives suplhur dioxide which is a high exothermic reaction. (∆H is -ve)

ii) Suphur dioxide on reaction with excess oxygen gives sulphur trioxide which is again an exothermic reaction. ( ∆H is -ve).

Now according to Hess's Law of constant Heat Summation :

The heat energy evolved for S(R) buring to form Sulphur trioxide is -297.5 + (-97.9) = -395.4 kJ

Hope this helps.