Question detail
Which option correctly separates bond breaking from bond making for CO2 + 2H2O -> CH4 + 2O2?
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. 814 kJ, endothermic
- B. -814 kJ, exothermic
- C. 0 kJ, no net energy change
- D. Incorrect bond-energy interpretation 4
Answer
The correct option is 814 kJ, endothermic.
Explanation
The correct option is 814 kJ, endothermic. Bonds broken: 2 × 805 + 4 × 463 = 3462 kJ. Bonds formed: 4 × 413 + 2 × 498 = 2648 kJ. Energy transferred = 3462 - 2648 = 814 kJ. The sign shows the reaction is endothermic. This comparison question 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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