Question detail

Using the supplied average bond energies, what is the energy transferred for 2HI -> H2 + I2 in The energy change of reactions (HT only)?

Try the question, check the answer, then read the explanation to understand the curriculum point.

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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 (HT only) Explain why a reaction is endothermic when energy needed to break bonds is greater than energy released from forming bonds and keeps bond breaking separate from bond making in The energy change of reactions (HT only).

Common mistake

Misunderstanding Endothermic Reactions

Students often think that endothermic reactions absorb energy without any comparison to the energy released from forming bonds.

Emphasize that an endothermic reaction occurs specifically when the energy required to break bonds is greater than the energy released when new bonds form.

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