Ncert Exercises & Solutions

Given below are two statements:

Assertion (A):	In the dissociation of PCl₅ at constant pressure and temperature, the addition of helium at equilibrium increases the dissociation of PCl₅.
Reason (R):	Helium reacts with Cl₂ .

1.	Both (A) and (R) are true and (R) is the correct explanation of (A).
2.	Both (A) and (R) are true but (R) is not the correct explanation of (A).
3.	(A) is true but (R) is false.
4.	(A) is false but (R) is true.

Hint: At constant pressure, volume changes and concentration of reactant and product changes.

The reaction is as follows:

{PCl}_{5} \to {PCl}_{3} + {Cl}_{2}

At constant pressure, when helium is added to the equilibrium, volume increases. Thus in order to maintain the K constant,

degree of dissociation of PCl₅ increases. Helium is unreactive towards chlorine gas.

Hence, Assertion is true but the reason is false.