Calculate the bond strength of O-H bond in `O-H` bond in `H_(2) O (g)` from the following data :
`H_(2) (g) to 2 H (g) , Delta H^(0) = 436 k J * "mol"^(-1)`
` (1)/(2) O_(2) (g) to O(g) , Delta H^(0) = 249 kJ * mol^(-1)`
`H_(2) (g) + (1)/(2) O_(2) (g) to H_(2) O (g) , DeltaH^(0) = - 241 kJ * mol^(-1)`

Explanation

`H_(2) (g) to 2 H (g) , DeltaH^(0) = 436 kJ * mol^(-1) " " … (i)`
` (1)/(2) O_(2) (g) to O (g) , Delta H^(0) = 249 kJ * mol^(-1) " " … (ii)`
`H_(2) (g) + (1)/(2) O_(2) (g) to H_(2) O (g) , Delta H^(0) = -241 kJ * mol^(-1) " " … (iii)`
By (i) + (ii) - (iii) we get ,

`Delta H^(0) = (436 + 249 + 241) = 926 kJ * mol^(-1) " " ... (iv)`
Equation (iv) indicates dissociation of O-H bonds present in 1 mol of `H_(2) O(g)` . The standard enthalpy change for this process `(Delta H^(0)) = 926kJ * mol^(-1)`
Number of O-H bonds present in 1 mol `H_(2)O =2` mol
`therefore` Energy required to break 2 mol O-H bonds = 926 kJ.
`therefore` Energy required to break 1 mol O-H bond = `(926)/(2) = 463 `kJ
`therefore` Strength of O-H bond in `H_(2)O (g) = 463 kJ * mol^(-1)` mk