If bond enthalpies of $\mathrm{N} \equiv \mathrm{N}, \mathrm{H}-\mathrm{H}$ and $\mathrm{N}-\mathrm{H}$…

If bond enthalpies of $\mathrm{N} \equiv \mathrm{N}, \mathrm{H}-\mathrm{H}$ and $\mathrm{N}-\mathrm{H}$ bonds are $x_{1}, \mathrm{x}_{2}$ and $\mathrm{x}_{3}$ respectively, $\Delta \mathrm{H}_{\mathrm{f}}^{\mathrm{o}}$ for $\mathrm{NH}_{3}$ will be
  1. $x_{1}+3 x_{2}-6 x_{3}$
  2. $1 / 2 \mathrm{x}_{1}+3 / 2 \mathrm{x}_{2}-3 \mathrm{x}_{3}$
  3. $3 x_{3}-1 / 2 x_{1}-3 / 2 x_{2}$
  4. $6 x_{3}-x_{1}-3 x_{2}$

Solution

$\frac{1}{2} \mathrm{~N}_{2}+\frac{3}{2} \mathrm{H}_{2} \longrightarrow \mathrm{NH}_{3}$
$\frac{1}{2} \mathrm{x}_{1}+\frac{3}{2} \mathrm{x}_{2}-3 \mathrm{x}_{3}$

Asked in: JEE-TOPICTESTS-CHEMISTRY

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