At 760◦C, Kc= 33.3 for the reaction PCl5(g)⇀↽PCl3(g) + Cl2(g) If a mixture that consists of 0.31 mol PCl3 and 0.22 mol Cl2 is placed in an 8 L reaction vessel and heated to 760◦C, what is the equilibrium composition of PCl5?Answer in units of mol/L.

Answer 1

0.31/8 = estimated 0.04 M for PCl3 but you need a better number for all of the calculations that follow.
0.22/8 = about 0.03 M for Cl2.

................PCl5(g)⇀↽PCl3(g) + Cl2(g)
I...................0...............0.04..........0.03
C.................+x............ -x...............-x
E..................+x............0.04-x......0.03-x
Plug the E line into Kc expression and solve for x M = (PCl5)
Kc = 33.3