✔ 最佳答案
The energy needed to break one mole of specific covalent bonds in gaseous state is called bond enthalpy.
i.e. ICl(g) → I(g) + Cl(g) ... ΔH = bond enthalpy of I-Cl bond
All reactants and products are in gaseous state. This is because there is no interactions (attractions and repulsions) between the gaseous particles (ideal gases), and thus all energy absorbed is used to break the bond.
Consider the equation you gave :
ICl(s) → I(g) + Cl(g) ... ΔH = +210 kJ mol-1
ICl is in solid state. 210 kJ mol-1 of energy is used to vaporize ICl(s) to ICl(g) and then break the bond. Therefore, the ΔH value is NOT the bond enthalpy of I-Cl bond.