How does the energy involved in bond making and bond breaking determine whether a reaction is endothermic or exothermic?
If more energy is required to break bonds than is released making bonds, the reaction is endothermic.
If more energy is released making bonds than is required to break bonds, the reaction is exothermic.
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What is the general formula for calculating ΔHr using the bond enthalpies of reactants and products?
ΔrH = Σ(bond enthalpies in reactants) - Σ(bond enthalpies in products)
Σ = sum of
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Why are all average bond enthalpy values positive?
Because energy is required to break bonds - it is an endothermic process.
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Describe the steps in calculating ΔHr using bond enthalpies.
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What are the units of average bond enthalpy?
kJ mol-1
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Explain which method gives a more accurate value of ΔH - using a Hess cycle or using mean bond enthalpies?
Using Hess cycles gives more accurate ΔH values because bond enthalpies are average values of many different molecules and not just the molecules in the reaction.
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What is the definition of bond energy?
Bond energy is the energy required to break one mole of a specified type of covalent bond in a gaseous molecule.
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