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) Calculate the overall energy change as energy needed to break bonds minus energy released when bonds form and keeps bond breaking separate from bond making in The energy change of reactions (HT only).
Common mistake
Mis‑applying the sign convention
Students often add the energy released when bonds form to the energy required to break bonds, giving a positive value for an exothermic reaction.
Remember the formula: ΔE = ΣE(bonds broken) – ΣE(bonds formed). For an exothermic reaction the second term is larger, so ΔE is negative, indicating energy is released.
Related flashcards
Flashcard 1 of 5
Related practice questions
Question 1 of 5
Choose an answer, get feedback, then move sideways through the set.