Calculate heat of formation of $\mathrm{HCl}$ gas from following reaction.…

Calculate heat of formation of $\mathrm{HCl}$ gas from following reaction. $\mathrm{H}_{2(\mathrm{~g})}+\mathrm{Cl}_{2(\mathrm{~g})} \rightarrow 2 \mathrm{HCl}_{(\mathrm{g})} ; \Delta \mathrm{H}=-194 \mathrm{~kJ}$
  1. $-143 \mathrm{~kJ} \mathrm{~mol}^{-1}$
  2. $-286 \mathrm{~kJ} \mathrm{~mol}^{-1}$
  3. $-92 \mathrm{~kJ} \mathrm{~mol}^{-1}$
  4. $-97 \mathrm{~kJ} \mathrm{~mol}^{-1}$

Solution

$\begin{aligned} & \mathrm{H}_{2(\mathrm{~g})}+\mathrm{Cl}_{2(\mathrm{~g})} \longrightarrow 2 \mathrm{HCl}_{(\mathrm{g})}, \Delta \mathrm{H}=-194 \mathrm{~kJ} \\ & \Delta \mathrm{H}_{\text {reaction }}=2 \Delta \mathrm{H}_{\mathrm{f}(\mathrm{HCl})}-\Delta \mathrm{H}_{\mathrm{f}\left(\mathrm{H}_2\right)}-\Delta \mathrm{H}_{\mathrm{f}\left(\mathrm{Cl}_2\right)} \\ & -194=2 \Delta \mathrm{H}_{\mathrm{f}(\mathrm{HCl})}-\mathrm{O}-\mathrm{O} \\ & \Delta \mathrm{H}_{\mathrm{f}(\mathrm{HCl})}=-194 / 2 \\ & =-97 \mathrm{~kJ} / \mathrm{mol}\end{aligned}$

Asked in: MHT CET 2021 (20 Sep Shift 1)

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