2024 O Level Chem P1 Q30 — Energetics / Bond Energies Solution
Question
1 The energy released when four O-H bonds are formed is more than the energy absorbed when the two H-H bonds and the O=O bond are broken.
2 The reaction has a positive ΔH value.
3 The temperature of the surroundings increases.
4 The diagram showing the energy changes for the reaction is . Which statements are correct?
Video Solution
Explanation
Answer: A. The combustion of hydrogen, \(2\text{H}_2 + \text{O}_2 \rightarrow 2\text{H}_2\text{O}\), is highly exothermic.
Statement 1 is correct: in any exothermic reaction, the energy released forming new bonds (4 O–H bonds in 2 \(\text{H}_2\text{O}\)) exceeds the energy absorbed breaking the original bonds (2 H–H + 1 O=O). The difference is the heat released.
Statement 3 is correct: an exothermic reaction warms its surroundings.
Statement 2 is wrong: \(\Delta H\) for an exothermic reaction is negative, not positive.
Statement 4 (energy diagram with reactants higher than products) is the opposite of what's required — exothermic profiles have reactants higher.
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