Question detail
A student totals bonds broken and bonds formed for CH4 + 2O2 -> CO2 + 2H2O. Which result and conclusion are correct?
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, exothermic
- B. 814 kJ, endothermic
- C. 0 kJ, no net energy change
- D. Incorrect bond-energy interpretation 4
Answer
The correct option is -814 kJ, exothermic.
Explanation
The correct option is -814 kJ, exothermic. Bonds broken: 4 × 413 + 2 × 498 = 2648 kJ. Bonds formed: 2 × 805 + 4 × 463 = 3462 kJ. Energy transferred = 2648 - 3462 = -814 kJ. The sign shows the reaction is exothermic. This application 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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