Chemistry
posted by JoJo .
17. You have the following equations:
2S (s) + 3O2 (g) 2SO3 (g), H = 792 kJ
2S (s) + 2O2 (g) 2SO2 (g), H = ?
2SO2 (g) + O2 (g) 2SO3 (g), H = 198 kJ
What is the missing H?

Add equation 1 to the reverse of equation 3 and I believe that will give you equation 2. Then add 792 to 198 to find the missing H.