S(g)+ 32O2(g) SO3(g)+2x kcal SO2(g)+ 12O2(g) SO3(g)+y kcal The heat of formation of SO2(g) is given by :
- 2x+y kcal
- 2xy kcal
- y-2x kcal
- x+y kcal
Answer
(3) y-2x kcal
Solution
Heat evolved H1=-2x, H2=-y
S+O2 SO2 = (1) - (2) (Hess's law)
Hf=-2x-(-y)=y-2x kcal
Answer: (3)