What is the concentration of the reactant, PCl5 at equilibrium?

Question

Consider the reaction.

PCl₅(g) ⇌ PCl₃(g) +Cl₂(g) K=0.042

The concentration of the products at equilibrium are [PCl₃] =0.13 M and [Cl₂] = 0.27 M.

What is the concentration of the reactant, PCl₅ at equilibrium?

[PCl₅] =? M

Answer 1

Everything you need is in the book.

Answer 2

Products over reactants with each concentration raised

to the power of its coefficient in the balanced equation.

In this case, each of the coefficients is 1, so

K = 0.042, [PCl₃] =0.13 M and [Cl₂] = 0.27 M, so