Answer is: concentration of chlorine is 1418.34 M.
Balanced chemical reaction: PCl₃(g) + Cl₂(g) → PCl₅(g).
[PCl₃] = 0.33 M; equilibrium concentration of phosphorus trichloride.
[PCl₅] = 0.44 M; equilibrium concentration of phosphorus pentachloride.
Keq = 0.00094.
Keq = [PCl₅] ÷ [PCl₃] · [Cl₂].
[Cl₂] = [PCl₅] ÷ Keq · [PCl₃].
[Cl₂] = 0.44 M ÷ 0.33 M · 0.00094.
[Cl₂] = 1418.43 M.
