How the concentration of the chlorine would be affected if the volume of the container is increased? $$\ce{4 HCl + O2 <=> 2 Cl2 + 2 H2O + $Q$}$$
My initial thought was that the total and partial pressures were decreased on increasing the volume of the container. But I did not account for the fact that the $\ce{HCl}$ did not play a role in this pressure.
So, according to my previous process, the reaction should proceed in the backward direction, concentration of $\ce{Cl2}$ should decrease. On the other hand, if we exclude the $\ce{HCl}$ factor, the reaction should proceed in forward direction increasing the concentration if $\ce{Cl2}$.
Please help me understand what will be the actual effect.