Consider the following reaction:
pcl5(g)⇌pcl3(g)+cl2(g)

select the equilibrium-constant expression for the reaction.
kc=[pcl3][cl2]/[pcl5]
kc=[pcl5]/[pcl3][cl2]
kc=[pcl5]/[pcl3]

initially, 0.63 mol of pcl5 is placed in a 1.0 l flask. at equilibrium, there is 0.12 mol of pcl3 in the flask. what is the equilibrium concentration of pcl5?
express your answer to two significant figures and include the appropriate units.

what is the equilibrium concentration of cl2?
express your answer to two significant figures and include the appropriate units.

if 0.25 mol of cl2 is added to the equilibrium mixture, will the concentration of pcl5 increase or decrease?

the concentration of pcl5 will increase.
the concentration of pcl5 will decrease.