Question detail
Calculate the energy change when 2 moles of methane (CH4) combust completely in oxygen (O2) to form carbon dioxide (CO2) and water (H2O). The bond energies are: C-H = 412 kJ/mol, O=O = 498 kJ/mol, C=O = 799 kJ/mol, and O-H = 463 kJ/mol. Use the balanced equation: CH4 + 2 O2 → CO2 + 2 H2O.
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At a glance
Question
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exam_style
Style
Topic
Exothermic and endothermic reactions
Question
Calculate the energy change when 2 moles of methane (CH4) combust completely in oxygen (O2) to form carbon dioxide (CO2) and water (H2O). The bond energies are: C-H = 412 kJ/mol, O=O = 498 kJ/mol, C=O = 799 kJ/mol, and O-H = 463 kJ/mol. Use the balanced equation: CH4 + 2 O2 → CO2 + 2 H2O.
Answer
-890 kJ.
Explanation
The correct option is exothermic reaction: correct Unit 4.5 answer for Energy transfer during exothermic and endothermic reactions. It directly supports the approved learning objective to identify combustion, many oxidation reactions and neutralisation as examples of exothermic reactions. This keeps the answer anchored to Energy transfer during exothermic and endothermic reactions within Exothermic and endothermic reactions, and avoids mixing energy transfer, reaction profiles, activation energy, chemical cells, fuel cells, exothermic reactions and endothermic reactions unless the objective names them.
Common mistake
Misidentifying a neutralisation as endothermic
Students often think that a neutralisation reaction, such as mixing an acid with a base, absorbs heat and is therefore endothermic.
Explain that neutralisation releases heat to the surroundings, making it an exothermic reaction, and that the temperature of the solution rises during the process.
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