Question

Consider the reaction

PCl₅ (g) −⇀ PCl₃ (g) + Cl₂ (g)

K_c = 0.0420

The concentration of the products at equilibrium are [PCl₃] = 0.120 M and [Cl₂] = 0.190 M.

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

[PCl₅] = ?

Answer 1

Equilibrium concentration of PCl₃= 0.170 M

Equilibrium concentration of Cl₂= 0.190 M

The equilibrium constant for the reaction K_c= 0.0420

The equation relating the equilibrium constant to the equilibrium concentrations of the reactants and products is:

$Kc=\frac{PCl3\times Cl2}{PCl5}$

$0.0420=\frac{0.170\times0.190}{PCl5}$

$PCl5=\frac{0.0420}{0.0323}$

PCl₅=1.3000