Question

Assertion :Assertion : In the dissociation of $PC{l}_5$ at constant pressure and temperature addition of helium at equilibrium increases the dissociation of $PC{l}_5$. Reason: Reason : Helium reacts with $C{l}_2$ and hence shifts the equilibrium in forward direction.

• A. If both the assertion and reason are true and reason is the correct explanation of assertion.
• B. If both the assertion and reason are true but reason is not the correct explanation of assertion.
• C. If assertion is true but reason is false.
• D. If both assertion and reason are false.

Answer 1

The correct option is C If assertion is true but reason is false.

$\left(I\right)$ The given reaction is :-

${PCl}_5\rightleftharpoons {PCl}_3\left(g\right)+{Cl}_2\left(g\right)$

$\left(g\right)$

Now, when $He$ is added; since it is an inert gas to it will not react with any of the reactants or products. Now, to keep the pressure of the reaction constant. The addition of $He$ has caused increase in volume of the system. Also, temperature of the system is kept constant. so, the volume of system gets increased and it will favour the forward reaction.

$\left(II\right)$ Since $He$ is inert; it do not reach with ${Cl}_2$.