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Chemistry · Unit 1 · Chemical reactions — reactants, products and energy change · Chemical reactions

Explain, in terms of average bond enthalpies, why reactions are exothermic or endothermic.

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Question 1

The combustion of methane is represented by the equation: \[ \text{CH}_4(g) + 2\text{O}_2(g) \rightarrow \text{CO}_2(g) + 2\text{H}_2\text{O}(g) \] Average bond enthalpies: C–H = 412 kJ mol\(^{-1}\), O=O = 496 kJ mol\(^{-1}\), C=O = 743 kJ mol\(^{-1}\), O–H = 463 kJ mol\(^{-1}\). Explain why this reaction is exothermic in terms of the average bond enthalpies given.

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Question 2

Which statement correctly explains why a reaction is exothermic?

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