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.
At a glance
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 describe how to measure temperature changes when substances react or dissolve in water. (AT 5) and keeps bond breaking separate from bond making in Energy transfer during exothermic and endothermic reactions.
Common mistake
Measuring Temperature Changes
Students often forget to account for the initial temperature of the water before adding the reactants, leading to inaccurate measurements of temperature change.
Always record the initial temperature of the water before starting the reaction to ensure accurate calculations of temperature change.
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