A-LevelChemistryChemical energetics9701/12 · Feb/Mar 2019 · Q81 Mark
The standard enthalpy changes of combustion of carbon, hydrogen and methanol are shown. C(s) + O₂(g) → CO₂(g) ∆Hᶜ = −394 kJ mol⁻¹ H₂(g) + ½O₂(g) → H₂O(l) ∆Hᶜ = −286 kJ mol⁻¹ CH₃OH(l) + 1½O₂(g) → CO₂(g) + 2H₂O(l) ∆Hᶜ = −726 kJ mol⁻¹ Which expression gives the standard enthalpy change of formation of methanol in kJ mol⁻¹?
A-394 + (-286) – (-726)
B-394 + (−286 × 2) – 726
C-394 + (−286 × 2) – (−726)
D-726 – (-394) – (−286 × 2)
✓ Correct answer
C: -394 + (−286 × 2) – (−726)
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