Question detail
Use the formula energy transferred equals bonds broken minus bonds formed for H2 + Br2 -> 2HBr. What should the final answer be?
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, exothermic
- B. 103 kJ, endothermic
- C. 0 kJ, no net energy change
- D. Incorrect bond-energy interpretation 4
Answer
The correct option is -103 kJ, exothermic.
Explanation
The correct option is -103 kJ, exothermic. Bonds broken: 1 × 436 + 1 × 193 = 629 kJ. Bonds formed: 2 × 366 = 732 kJ. Energy transferred = 629 - 732 = -103 kJ. The sign shows the reaction is exothermic. This calculation 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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