Bond dissociation enthalpy of `F_(2)(158.8 " kJ mol"^)-1))` is less than that of `Cl_(2)(242.6 " kJ mol"^(-1))`. As a result, N-F bond is smaller as well as more stable as compared to N-Cl bond. Therefore, `NF_(3)` is more stable (exothermic) as compared to `NCl_(3)` (endothermic).
