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2017 O Level Chem P1 Q14 — Energy Changes / Bond Energy Solution

Energy Changes / Bond Energy 2017 O Level Pure Chemistry · Paper 1 · Q14

Question

The equation for the combustion of hydrogen is shown. 2H₂(g) + O₂(g) → 2H₂O(g) What is the enthalpy change of this reaction? Question diagram

Question diagram

A−482 kJ/mol
B−444 kJ/mol
C+444 kJ/mol
D+482 kJ/mol

Correct answer: A

Video Solution

Explanation

Answer: A. \(\Delta H\) = (energy to break bonds) minus (energy to make bonds). Bonds broken: 2 (H-H) and 1 (O=O) = \(2(436) + 498 = 1370\) kJ. Bonds formed: each water molecule has 2 (O-H) bonds, so \(2\text{H}_2\text{O}\) has 4 (O-H) = \(4(463) = 1852\) kJ.

\(\Delta H = 1370 - 1852 = -482\) kJ/mol.

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