Question detail
Show the working for the energy transferred in 2HI -> H2 + I2 using average bond energies in Reaction profiles.
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 working for the energy transferred in 2HI -> H2 + I2 using average bond energies in Reaction profiles.
Answer
9 kJ. The reaction is endothermic.
Explanation
The correct option is 9 kJ, endothermic. Bonds broken: 2 × 298 = 596 kJ. Bonds formed: 1 × 436 + 1 × 151 = 587 kJ. Energy transferred = 596 - 587 = 9 kJ. The sign shows the reaction is endothermic. This supports the approved objective to draw a simple reaction profile for an endothermic reaction and keeps bond breaking separate from bond making in Reaction profiles.
Common mistake
Mislabeling Reaction Profiles
Students often label the energy change in an endothermic reaction profile incorrectly, indicating it as a decrease instead of an increase.
Remember that in an endothermic reaction, the products have more energy than the reactants, so the energy change should be labeled as an increase.
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