Phosphorous pentachloride decomposes according to the reaction PCl5(g)=PCl3(g)+Cl2(g)

A 12.3 g sample of PCl5 is added to a sealed 1.50 L flask and the reaction is allowed to come to equilibrium at a constant temperature. At equilibrium, 31.8% of the PCl5 remains. What is the equilibrium constant, Kc, for the reaction?

Question is asking for Kc

The equilibrium constant, , for the reaction is 0.061.

Explanation:

Initial concentration of  =  

Equilibrium concentration of =  

The given balanced equilibrium reaction is,

Initial conc.              0.039 M                0 M        0 M

At eqm. conc.     (0.039-x) M              (x) M   (x) M

Given : (0.039-x) = 0.012

x = 0.027

The expression for equilibrium constant for this reaction will be,

Now put all the given values in this expression, we get :

The equilibrium constant, , for the reaction is 0.061.