Question detail
Which option correctly separates bond breaking from bond making for 2H2 + O2 -> 2H2O?
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
MCQ
Type
practice
Style
Topic
Exothermic and endothermic reactions
Question
- A. -482 kJ, exothermic
- B. 482 kJ, endothermic
- C. 0 kJ, no net energy change
- D. Incorrect bond-energy interpretation 4
Answer
The correct option is -482 kJ, exothermic.
Explanation
The correct option is -482 kJ, exothermic. Bonds broken: 2 × 436 + 1 × 498 = 1370 kJ. Bonds formed: 4 × 463 = 1852 kJ. Energy transferred = 1370 - 1852 = -482 kJ. The sign shows the reaction is exothermic. This comparison question supports the approved objective to (HT only) Explain that bond energies can be used to calculate energy needed to break bonds and keeps bond breaking separate from bond making in The energy change of reactions (HT only).
Common mistake
Misunderstanding Bond Energies
Students often confuse bond energies with the energy changes in reaction profiles, thinking they are the same concept.
Clarify that bond energies specifically refer to the energy required to break bonds, while reaction profiles illustrate the overall energy changes during a reaction.
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