Chem II
posted by Sam on .
PCl5 dissociates according to the reaction: PCl5(g) ↔ PCl3(g) + Cl2(g). One mole of PCl5 was placed in one liter of solution. When equilibrium was established, 0.5 mole of PCl5 remained in the mixture. What is the equilibrium constant for this reaction?

............PCl5 ==> PCl3 + Cl2
initial......1.0M......0......0
change.......x.......x.......x
equil.......1x.......x.......x
The problem tells you that 1x = 0.5; therefore, x = 1.00.5= 0.5M which means Pl3 = 0.5M and Cl2 = 0.50M
Then K = (PCl3)(Cl2)/(PCl5) \
Substitute and solve for K. 
thank you