When this system is at equilibrium at a certain temperature PCl5(g) ⇋ PCl3(g) + Cl2(g), the concentrations are found to be [PCl5] = 0.40 M, [PCl3] = [Cl2] = 0.20. If the volume of the container is suddenly halved at the same temperature, what will be the new equilibrium concentration of PCl5?

The new concentration of will be 0.9 M.

Explanation:

The equilibrium concentration of all species:

The equilibrium constant's expression can be written as:

On halving the volume of the container, the concentration will get doubled;

0.80 M                                         0.40M   0.40 M

Reaction will go backward.

Initially

0.80 M                                         0.40M   0.40 M

After reestablishment of an  equilibrium

(0.80+x) M                                         (0.40-x)M   (0.40-x) M

So, the equilibrium expression for above reaction can be written as :

x = 0.1 M

The new concentration of will be:

its first and third is your answer i did the qustion the fourth isnt right