I have another question.
The compound PCl5 decomposes into Cl2 and PCl3. The equilibrium of PCl5(g) Cl2(g) + PCl3(g) has a Keq of
2.24 x 10-2 at 327o C. What is the equilibrium concentration of Cl2 in a 1.00 liter vessel containing 0.235 mole of PCl5 and 0.174 mole of PCl3?

what's the formular for that because they already gave Keq or do I use that formula ans work backwards?

The procedure should be the same. Given a general reaction

w A + x B = y C + z D

where w, x, y, and z are the numeric coefficients and A, B, C, and D are the reactants and products, the following is the definition of Keq:

K_{eq} = \frac{[A]^w\, [B]^x}{[C]^y\, [D]^z}

Give it a shot and post your work. I'll let you know if you're on the right track.