Question detail

For The energy change of reactions (HT only), use bond energies to answer this calculation check: what is the energy transferred for H2 + Cl2 -> 2HCl?

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. -184 kJ, exothermic
B. 184 kJ, endothermic
C. 0 kJ, no net energy change
D. Incorrect bond-energy interpretation 4

Answer

The correct option is -184 kJ, 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 calculation question supports the approved objective to (HT only) Calculate the total energy needed to break bonds in reactants from supplied bond energies. (MS 1a) and keeps bond breaking separate from bond making in The energy change of reactions (HT only).

Common mistake

Misunderstanding Bond Energy Calculations

Students often confuse the total energy needed to break bonds with the energy released when bonds form, leading to incorrect calculations.

To fix this, students should clearly separate the energy needed to break bonds from the energy released when bonds form, ensuring they apply the correct formula for each part.

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