Equilibrium constant equation

Question

We have 0.01mol/l FeCl3 and 0.01mol/l NH4SCN, what is the equilibrium constant for this reaction?

Answer 1

The reaction is:

FeCl₃(aq) + NH₄SCN(aq) ==> Fe(SNC))Cl₂(aq) + NH₄Cl(aq)

K_eq = [Fe(SCN)Cl₂]][NH₄Cl]/[FeCl₃][NH₄(SCN)]

In order to determine an actual value of Keq, one needs to know the concentrations of each species at equilibrium. We are given only the concentrations of reactants initially present, so the best we can do is re-write the expression in terms of x, but we cannot determine a value without knowing additional information.

K_eq = (x)(x)/(0.01-x)(0.01-x)