$\ce{PCl5 <=> PCl3 +Cl2} $
It's stated in my book that addition of $\ce{PCl5}$ to the equilibrium mixture increases the rate of forward reaction but no reason is mentioned for it.
However, before this the author derived $K_c = \dfrac{x^2}{(1-x)V}$ (using law of mass action at equilibrium ) where V is the volume of the container and $x$ is the number of $\ce{PCl5}$ molecules dissociated from $a$ number of moles initially. I couldn't relate the "rate of forward reaction" statement to this equation while earlier in case of the reaction:
$\ce{H2 + I2 <=> HI}$
I was able to relate the equation I obtained through law of mass action with the effect of concentration on rate of forward or backward reaction.
Could someone please explain why addition of $\ce{PCl5}$ to the equilibrium mixture increases the rate of forward reaction?