Question detail
Show the diagram working for the energy transferred in H2 + I2 -> 2HI 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 diagram working for the energy transferred in H2 + I2 -> 2HI using average bond energies in The energy change of reactions (HT only).
Answer
-9 kJ. The reaction is exothermic.
Explanation
The correct option is -9 kJ, exothermic. Bonds broken: 1 × 436 + 1 × 151 = 587 kJ. Bonds formed: 2 × 298 = 596 kJ. Energy transferred = 587 - 596 = -9 kJ. The sign shows the reaction is exothermic. This diagram question supports the approved objective to (HT only) Explain why a reaction is exothermic when energy released from forming bonds is greater than energy needed to break bonds and keeps bond breaking separate from bond making in The energy change of reactions (HT only).
Common mistake
Misunderstanding Exothermic Reactions
Students often think that exothermic reactions absorb energy from the surroundings instead of releasing it.
Remember that exothermic reactions release energy to the surroundings, resulting in an increase in temperature.
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