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A 1.0 liter container is filled with 0.300 M of
PCl5 at 250◦C. The vessel is then held at a
constant temperature until the reaction
PCl5(g) ⇀↽ PCl3(g) + Cl2(g)
comes to equilibrium. It is found that the
vessel contains 0.200 moles of PCl5. What is
the value of the equilibrium constant for the
reaction at this temperature?