Question detail
Show the working for the energy transferred in H2 + Cl2 -> 2HCl using average bond energies in Energy transfer during exothermic and endothermic reactions.
Try the question, check the answer, then read the explanation to understand the curriculum point.
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Question
Type
exam_style
Style
Topic
Exothermic and endothermic reactions
Question
Show the working for the energy transferred in H2 + Cl2 -> 2HCl using average bond energies in Energy transfer during exothermic and endothermic reactions.
Answer
-184 kJ. The reaction is exothermic.
Explanation
The correct option is -184 kJ, exothermic. Bonds broken: 1 × 436 + 1 × 242 = 678 kJ. Bonds formed: 2 × 431 = 862 kJ. Energy transferred = 678 - 862 = -184 kJ. The sign shows the reaction is exothermic. This supports the approved objective to explain that the temperature of the surroundings increases during an exothermic reaction and keeps bond breaking separate from bond making in Energy transfer during exothermic and endothermic reactions.
Common mistake
Surroundings temperature change
Students think the temperature of the surroundings decreases during an exothermic reaction
Explain that in an exothermic reaction energy is released to the surroundings, so their temperature rises
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