a. Since P4 and PCl3 are a pure solid and a pure liquid, respectively, we need to consider only the effect of the decrease in volume on Cl2. The position of the equilibrium will shift to the right, since the reactant side contains six gaseous molecules and product side has none.b. Decreasing the volume will shift the given reaction to the right, since the product side contains only one gaseous molecule and the reactant side has two.c. Both sides of the balanced reaction equation have four gaseous molecules. A change in volume will have no effect on the equilibrium position. There is no shift in this case..