# Why does the addition of PCl5 increase the rate of dissociation of PCl5?

$\ce{PCl5 <=> PCl3 +Cl2}$

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?

To your question: To model this system using my example of immigration, we suddenly add an enourmous influx of refugees into the old kingdom (Increase in $\ce{PCl5}$).