Estimate ΔH° (kJ) for the combustion of methanol vapour using the average bond enthalpies (kJ/mol): C-H = 413, C-O = 358, O-H = 463, O=O = 498, C=O (in CO₂) = 805.
$C H_{3} OH (g) + \frac{3}{2} O_{2} (g) \to C O_{2} (g) + 2 H_{2} O (g)$

Question

Estimate ΔH° (kJ) for the combustion of methanol vapour using the average bond enthalpies (kJ/mol): C-H = 413, C-O = 358, O-H = 463, O=O = 498, C=O (in CO₂) = 805.

$C H_{3} OH (g) + \frac{3}{2} O_{2} (g) \to C O_{2} (g) + 2 H_{2} O (g)$

TestHub · Accepted Answer

Bonds broken: 3 C-H + 1 C-O + 1 O-H + 1.5 O=O = 1239 + 358 + 463 + 747 = 2807 kJ. Bonds formed: 2 C=O + 4 O-H = 1610 + 1852 = 3462 kJ. ΔH = 2807 - 3462 = -655 kJ. Answer: (D).

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