The formation enthalpies, ΔHf^Θ for H(g) and O(g) are 220.0 and 250.0 kJ mol^{–1},

Question

The formation enthalpies, \(\Delta \mathrm{H}_{\mathrm{f}}^{\Theta}\) for \(\mathrm{H}_{(\mathrm{g})}\) and \(\mathrm{O}_{(\mathrm{g})}\) are 220.0 and \(250.0 \mathrm{~kJ} \mathrm{~mol}^{-1}\), respectively, at 298.15 K , and \(\Delta \mathrm{H}_{\mathrm{f}}^{-}\) for \(\mathrm{H}_{2} \mathrm{O}_{(\mathrm{g})}\) is \(-242.0 \mathrm{~kJ} \mathrm{~mol}^{-1}\) at the same temperature. The average bond enthalpy of the \(\mathrm{O}-\mathrm{H}\) bond in water at 298.15 K is _____ \(\mathrm{kJ} \mathrm{mol}{ }^{-1}\) (nearest integer).

Answer 1

Answer is : 466

\(\frac{1}{2} \mathrm{H}_{2(\mathrm{~g})} \rightarrow \mathrm{H}(\mathrm{g}) \ ;\ \Delta_{\mathrm{f}} \mathrm{H}_{}\left(\mathrm{H}_{(\mathrm{g})}\right)=220 \mathrm{KJ} / \mathrm{mol}\) 

\( \frac{1}{2} \mathrm{O}_{2(\mathrm{~g})} \rightarrow \mathrm{O}(\mathrm{g}) \ ; \ \Delta_{\mathrm{f}} \mathrm{H}\left(\mathrm{O}_{(\mathrm{g})}\right)=250 \mathrm{KJ} / \mathrm{mol}\) 

 

\( \Delta \mathrm{H}_{\mathrm{f}}\left(\mathrm{H}_{2} \mathrm{O}_{(\mathrm{l})}\right)=-242=440+250-2( B.E.(O - H))\) 

\(BE(O - H) = 466\ KJ / mol\)