Question detail
Show the comparison 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 comparison 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 comparison question supports the approved objective to (HT only) Calculate the total energy released when bonds form in products from supplied bond energies. (MS 1a) and keeps bond breaking separate from bond making in The energy change of reactions (HT only).
Common mistake
Misunderstanding Bond Energies
Students often confuse the total energy released when bonds form with the energy needed to break bonds, leading to incorrect calculations.
To fix this, students should clearly differentiate between the energy required to break bonds and the energy released when bonds form, ensuring they follow the correct steps in calculations.
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