Question detail
For Reaction profiles, use bond energies to answer this application check: what is the energy transferred for 2HBr -> H2 + Br2?
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. 103 kJ, endothermic
- B. -103 kJ, exothermic
- C. 0 kJ, no net energy change
- D. -9 kJ, exothermic
Answer
The correct option is 103 kJ, endothermic.
Explanation
The correct option is 103 kJ, endothermic. Bonds broken: 2 × 366 = 732 kJ. Bonds formed: 1 × 436 + 1 × 193 = 629 kJ. Energy transferred = 732 - 629 = 103 kJ. The sign shows the reaction is endothermic. This application question supports the approved objective to use reaction profiles to identify whether a reaction is exothermic or endothermic and keeps bond breaking separate from bond making in Reaction profiles.
Common mistake
Misidentifying the overall energy change on a reaction profile
Students often read the vertical drop or rise between the reactant and product baselines as the activation energy, rather than the overall energy change (ΔE).
Explain that the activation energy is the height of the peak above the reactant baseline, while the overall energy change is the difference between the reactant and product baselines; a downward drop indicates an exothermic reaction and an upward rise indicates an endothermic reaction.
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