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Equilibrium — Chemistry STD 11 Science — Question

Gujarat BoardEnglish MediumSTD 11 ScienceChemistryEquilibrium1 Mark
Question
At 473 K , equilibrium constant $\mathrm{K}_{\mathrm{c}}$ for decomposition of phosphorus pentachloride, $\mathrm{PCl}_5$ is $8.3 \times 10^{-3}$. If decomposition is depicted as,
$\text{PCl}_5\text{ (g)}\rightleftharpoons\text{PCl}_3\text{ (g) + Cl}_2\text{ (g)}\ \Delta_\text{r}\text{H}^\ominus=124.0\text{ kJ mol}^{-1}$
what would be the effect on Kc if
  1. more PCl5 is added
  2. pressure is increased
  3. the temperature is increased?
✓

Answer

$\text{PCl}_{5\text{(g)}}\rightleftharpoons\text{PCl}_{3\text{(g)}}+\text{Cl}_{2\text{(g)}}$
  1. If more $\text{PCl}_5$ is added, then $\text{Q}_\text{c}$ becomes less than $\text{K}_{\text{c}'}$ the reaction will shift in the forward direction.
  2. If the pressure is increased, the reaction will shift towards backward direction as it contains less number of gaseous species. $\text{K}_\text{c}$ remains constant.
  3. As the reaction is endothermic, the increase in temperature will favour the forward reaction. More $\text{PCl}_5$ will dissociate to form $\text{PCl}_3$ and $\text{Cl}_2.$ $\text{K}_\text{c}$ increases.

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