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Equilibrium — Chemistry STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceChemistryEquilibrium5 Marks
Question
Four moles of $\mathrm{PCl}_5$ are heated in a closed $4 \mathrm{dm}^3(\mathrm{~L})$ container to reach equilibrium at 400 K . At equilibrium $50 \%$ of $\mathrm{PCl}_5$ is dissociated. What is the value of $\mathrm{K}_{\mathrm{c}}$ for the dissociation of $\mathrm{PCl}_5$ into $\mathrm{PCl}_3$ and $\mathrm{Cl}_2$ at 400 K .
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Answer

$\begin{matrix}&\text{PCl}_5(\text{g})&\rightleftharpoons&\text{PCl}_3(\text{g})&+&\text{Cl}_2(\text{g})\\\text{Initial Conc. }&4&&0&&0\\\text{Final Conc.at equilibrium}&4-\frac{4\times50}{100}&&2&&2\end{matrix}$
$\begin{matrix}\text{Final conc.in mol L}^{-1}&\frac{2}{4}&\frac{2}{4}&\frac{2}{4}\end{matrix}$
$\text{K}_{\text{c}}=\frac{[\text{PCl}_3][\text{Cl}_2]}{[\text{PCl}_5]}$
$=\frac{\frac{1}{2}+\frac{1}{2}}{\frac{1}{2}}=0.5$

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