Question detail
In a reaction where 3 moles of CH4 are combusted, calculate the energy change using the bond enthalpies: C-H is 412 kJ/mol and O=O is 498 kJ/mol, and the products are CO2 and H2O. Identify the bonds broken and formed.
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At a glance
Question
Type
exam_style
Style
Topic
Energetics
Question
In a reaction where 3 moles of CH4 are combusted, calculate the energy change using the bond enthalpies: C-H is 412 kJ/mol and O=O is 498 kJ/mol, and the products are CO2 and H2O. Identify the bonds broken and formed.
Answer
The energy change is -2100 kJ. This answer is anchored to Bond enthalpies.
Explanation
The energy change is -2100 kJ. is the best answer because it directly supports the AQA A-Level Chemistry objective to distinguish bonds broken from bonds formed in bond enthalpy calculations. This reasoning is anchored to Bond enthalpies in Energetics, and it separates bonds formed from similar A-Level ideas rather than relying on a vague recall statement. Other options are weaker if they use the wrong evidence, calculation, mechanism, observation, unit, or conclusion for this subtopic.
Common mistake
Distinguishing Bonds in Calculations
Students often confuse bonds broken with bonds formed when calculating enthalpy changes.
Bonds broken refer to the bonds that need to be broken in the reactants, while bonds formed refer to the bonds created in the products. When calculating enthalpy changes, it is crucial to identify which bonds are being broken and which are being formed to accurately determine the energy change.
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