9.4Strengths of Ionic and Covalent Bonds
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ΔH = ΣDbonds broken − ΣDbonds formed subtracts one sum from another; treating it as an addition (or forgetting which group is being subtracted) flips exothermic and endothermic in the answer even when every individual bond energy was looked up correctly.
- Applies5.8Modeling Using Variation
Lattice energy ΔHlattice = C(Z⁺)(Z⁻)/Ro is a joint-variation relationship — directly proportional to the product of the ionic charges and inversely proportional to interionic distance — which is why doubling both charges while holding Ro fixed quadruples the lattice energy rather than doubling it.