Given (a) S(s) + O₂(g) → SO₂(g), ΔH = -297 kJ; (b) SO₂(g) + ½O₂(g) → SO₃(g), ΔH = -99 kJ. What is ΔH for S(s) + 3/2 O₂(g) → SO₃(g)?
Answer and explanation
Correct answer: C. -396 kJ
- Step 1: The target equation equals (a) + (b).
- Step 2: ΔH values combine in the same way: ΔH = -396 kJ.
Answer
-396 kJ.
Why not the others: -198 kJ: equation (b) was reversed even though it already points the right way. 396 kJ: the sign is reversed. -297 kJ: only equation (a) was used.
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