Question detail
Using the supplied average bond energies, what is the energy transferred for 2HI -> H2 + I2 in Energy transfer during exothermic and endothermic reactions?
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. 9 kJ, endothermic
- B. -9 kJ, exothermic
- C. 0 kJ, no net energy change
- D. Incorrect bond-energy interpretation 4
Answer
The correct option is 9 kJ, 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 distinguish between exothermic and endothermic reactions using the temperature change of the surroundings and keeps bond breaking separate from bond making in Energy transfer during exothermic and endothermic reactions.
Common mistake
Misinterpreting temperature change as energy direction
Students think that a rise in temperature of the surroundings means the reaction is endothermic, and a fall means exothermic.
Explain that in an exothermic reaction energy is released to the surroundings, raising their temperature; in an endothermic reaction energy is absorbed from the surroundings, lowering their temperature.
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