$H_{2(g)} + \frac{1}{2} O_{2(g)} \to H_2O_{(g)}$
$B.E. (H-H) = x_1$; $B.E. (O=O) = x_2$;
$B.E. (O-H) = x_3$
Heat of vaporisation of water $= x_4$,then $\Delta H_f$ [heat of formation of liquid water] is:

  • A
    $x_1 + \frac{x_2}{2} - x_3 + x_4$
  • B
    $2x_3 - x_1 - \frac{x_2}{2} - x_4$
  • C
    $x_1 + \frac{x_2}{2} - 2x_3 - x_4$
  • D
    $x_1 + \frac{x_2}{2} - 2x_3 + x_4$

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If the bond energies of $H-H$,$Br-Br$ and $H-Br$ are $433$,$192$ and $364 \ kJ \ mol^{-1}$ respectively,the $\Delta H^o$ for the reaction,$H_{2(g)} + Br_{2(g)} \to 2HBr_{(g)}$ is.....$kJ$

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