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 compare the relative energies of reactants and products in exothermic and endothermic reaction profiles and keeps bond breaking separate from bond making in Reaction profiles.
Common mistake
Confusing Reactant and Product Energies
Students often confuse the energy levels of reactants and products in exothermic and endothermic reaction profiles, leading to incorrect conclusions about energy transfer.
To fix this, students should practice drawing and labeling reaction profiles, ensuring they clearly identify the energy levels of both reactants and products, and remember that in exothermic reactions, products have lower energy than reactants, while in endothermic reactions, products have higher energy.
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