Question

Phosphorus pentachloride, PCl₅, an important reagent in organic chemistry for converting alcohols to alkyl chlorides (ROH ---> RCl), is hydrolyzed in water to form phosphoric acid and hydrogen chloride. In the gaseous state, however, PCl₅ can decompose at 250^oC according to the following reaction PCl_5(g) <---> PCl_3(g) + Cl_2(g), for which K = 0.0240.

1. Are products or reactants favored in the decomposition of PCl_5(g)?

2. If a 5.00-L flask containing 205.5 g PCl_5(g) is heated to 250^oC, what is the equilibrium concentration of each species in this reaction?

3. What effect would an increase in pressure have on the equilibrium position? Why?

4. If a 2500.-L vessel containing 3250. kg of PCl3_(g) with a constant chlorine pressure of 3.525 atm is allowed to reach equilibrium, how many kilograms of PCl_5(g) are produced?  

Answer 1

PCl₅ PC₃ + Cl₂ K = 0.0240 = 2.4 10^-2

1)

10^-3 K 10³ Both reactant and product equally stable

So both are equally favourable for the decomposition of PCl₅

2)

W_PCl5 = 205.5 gm

PCl₅    PC₃ + Cl₂

t=0 0.987 mole 0 0

t= eq. 0.987 - x x x

equilibrium concentrations are

x = 0.289

So the equilibrium concentrations are :-

3)

Reaction will shift in the backward direction

Reason :-

Pressur increases

Volume decreases

Reaction will shift in the direction where gaseous moles are less