Question

A concentration of PCL5(g),4,0 mol/L, verifies that the process PCl5(g) = PCl3(g) + Cl2(g)
is achieved with a degree of balance of 20% Calculate the equilibrium of the reaction constant

Answer 1

This is a very oddly worded question and I'm not sure what the question is. I will restate what I think it is.
A concn of PCl5 at equilibrium is 4 mols/L. The reaction yield was 20%. Calculate Keq.

Let y = initial concentration and x = change as equilibrium is established.

.......PCl5 ==> PCl3 + Cl2
I......y.........0......0
C.....-x.........x......x
E.....y-x........x......x

The problem, as I've worded it, states that y-x = 4 and the 4 is 20% of the initial concentration. So y must be 20 (4/0.2 = 20)
Therefore y-x = 4 = (PCl5)
x = 16 = PCl3 = Cl2

Plug those values into the Keq constant expression and solve for Keq.

Answer 2

Thank you :D