Average bond-enthalpy tables give the most reliable estimates for reactions in which

Core Concept

Tabulated bond enthalpies are measured for gas-phase molecules, where each bond is isolated from neighboring interactions. Applying them to liquids or solids adds error because intermolecular attractions and lattice energies are ignored. The method serves endothermic and exothermic reactions equally, provided the gas-phase assumption roughly holds. Deviations grow whenever condensed phases take part significantly.