The bond enthalpy values of H-H, O=O bonds are 436 kJ/mole and 498 kJ/mole respectively. Standard enthalpy of formation of water is -286 kJ/mole. The bond enthalpy of O-H bond is equal to-----kJ/mole

H-H+12O=O → 2O-H, H=-286 kJ ;+436+12498 +-2x =-286 ;                                          x=436+249+2862                                          x=485.5 kJ ;        O-H bond enthalpy=485.5 kJ/mole ;