Q. 0.6 mole of $PCl_{5},0.3$ mole of $PCl_{3}$ and 0.4 mole of $Cl_{2}$ are taken in a 1 L flask to obtain the following equilibrium
$PCl_{5}\left(\right.g\left.\right)\rightleftharpoonsPCl_{3}\left(\right.g\left.\right)+Cl_{2}\left(\right.g\left.\right)$
If the equilibrium constant $K_{c}$ for the reaction is 0.15. Predict the direction of the reaction.

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Solution:

$PCl_{5}\left(\right.g\left.\right)\rightleftharpoonsPCl_{3}\left(\right.g\left.\right)+Cl_{2}\left(\right.g\left.\right)$
$Q_{c}=\frac{0.4 \times 0.3}{0.6}=0.2$
$K_{c}=0.15$ since $Q_{c}>K_{c}$ reaction will proceed in backward direction.