For the reaction
`PCl_(5)(g)hArrPCl_(3)(g)+Cl_(2)(g)`
Which of the following sketches may represent above equilibrium? Assume equilibrium can be achieved from either side and by taking any one or more components initially. Give `K_(c )` for the reaction `lt 2`?

Options

A.
B.
C.
D.

Answer

D

Explanation

Given :`K_(c) < 2 for PCl_(5)(g) rarr PCl_(3)(g) + Cl_(2)(g)`
(A) From graph, find the value of `K_(c)`
`K_(c) = ([PCl_(3)][Cl_(2)]/[PCl_(5)])_(Eq) = 4 xx 6/2 > 2`
(A) is incorrect
(B)Incorrect : Since the concentration of both `PCl_(3)(g) and Cl_(2)(g)` will either increase or decrease. Here it is increasing for `Cl_(2)(g)` and decreasing for `PCl_(3)(g)`.
(C) Note that (from graph) the initial concentration of `PCl_(5)` is zero. So the equilibrium is established as follows.`PCl_(3)(g) + Cl_(2)(g) rarr PCl_(5)(g)`
(D)Obviously this should be the correct choice.However let us check it. Find `K_(c)`
`K_(c) = ([PCl_(3)][Cl_(2)]/[PCl_(5)])_(Eqm) = 2 xx 4/6 < 2`