Question detail
Show the application working for the energy transferred in H2 + Br2 -> 2HBr using average bond energies in The energy change of reactions (HT only).
Try the question, check the answer, then read the explanation to understand the curriculum point.
At a glance
Question
Type
exam_style
Style
Topic
Exothermic and endothermic reactions
Question
Show the application working for the energy transferred in H2 + Br2 -> 2HBr using average bond energies in The energy change of reactions (HT only).
Answer
-103 kJ. The reaction is 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 application question supports the approved objective to (HT only) Explain that bond energies can be used to calculate energy released when bonds form 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 overall energy change of a reaction, thinking that bond energies alone determine whether a reaction is exothermic or endothermic.
Emphasize that bond energies are used to calculate the energy released when bonds form, and this must be compared to the energy needed to break bonds to determine the overall energy change.
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