In the following system, PCl5(g) PCl3(g) + Cl2(g) at equilibrium, upon addition of xenon gas at constant T & p, the concentration of
- PCl5, PCl3 & Cl2 remain constant
- PCl3 will increase
- Cl2 will decrease
- PCl5 will increase
Answer
(2) PCl3 will increase
Solution
Xenon is an inert gas, and adding it at constant T and p increases the total volume of the mixture.
Every mole fraction xi therefore decreases, so the partial pressure of each reacting gas, pi = xi p, falls.
Qp = pPCl3 pCl2pPCl5 = nPCl3 nCl2nPCl5 pntotal
ntotal increases, Qp < Kp, and by Le Chatelier's principle the equilibrium shifts in the forward direction, towards more gaseous moles ( ng = +1).
More PCl5 dissociates; PCl3 (and Cl2) are formed, so PCl3 will increase.
Answer: (2)