Question detail

Using the supplied average bond energies, what is the energy transferred for 2HI -> H2 + I2 in Energy transfer during exothermic and endothermic reactions?

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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 identify thermal decomposition and the reaction of citric acid with sodium hydrogencarbonate as examples of endothermic reactions and keeps bond breaking separate from bond making in Energy transfer during exothermic and endothermic reactions.

Common mistake

Confusing Endothermic Reactions

Students often confuse thermal decomposition with exothermic reactions, thinking they release energy instead of absorbing it.

Remember that thermal decomposition is an endothermic reaction that takes in energy from the surroundings, while exothermic reactions release energy.

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For Energy transfer during exothermic and endothermic reactions, which answer best supports this AQA GCSE Chemistry Unit 4.5 objective: Identify thermal decomposition and the reaction of citric acid with sodium hydrogencarbonate as examples of endothermic reactions?