Consider the reaction.

Question

PCl5(g)↽−−⇀PCl3(g)+Cl2(g)𝐾c=0.0420

The concentrations of the products at equilibrium are [PCl3]=0.110 M and [Cl2]=0.230 M. What is the concentration of the reactant, PCl5, at equilibrium?

[PCl5]=_____M

Answer 1

The equilibrium constant for gases in terms of their concentrations, K_c, is the ratio of concentrations of the products over the concentrations of the reactants. In general, for the reaction:

aA + bB ↔ cC + dD

We get:

K = [C]^c[D]^d /([A]^a[B]^b)

Here, the equilibrium expression is as follows:

K_c = [PCl₃]¹[Cl₂]¹/[PCl₅]¹

Since we want to find [PCl₅], let's solve for it:

[PCl₅] = [PCl₃]*[Cl₂] / K_c

Now we'll substitute values:

[PCl₅] = 0.110*0.230/0.0420 = 0.602

So we get:

[PCl₅] = 0.602 M