Question

For the given reaction:
$PC{l}_5\left(g\right)\rightleftharpoons PC{l}_3\left(g\right)+C{l}_2\left(g\right),$ the forward reaction at a constant temperature is favoured by which of the following conditions?

• A. Introducing an inert gas at a constant volume.
  
• B. Introducing chlorine gas in the container.
  
• C. Introducing an inert gas at a constant pressure.
  
• D. Increasing the volume of the container.

Answer 1

Answer: (C), (D)

The correct options are
C Introducing an inert gas at a constant pressure.

D Increasing the volume of the container.

Option A: When an inert gas is added to the system in equilibrium at constant volume, the total pressure will increase. But the concentrations of the products and reactants will not change
Hence, when an inert gas is added to the system in equilibrium at constant volume there will be no effect on the equilibrium.

Option B: Applying Le-Chatelier's principle, for a reaction at equilibrium, introducing more products will shift the reaction towards the reactant side so as to oppose the change caused by adding more products. So the reaction will shift backwards on addition of chlorine gas.

Option C: Addition of an inert gas at constant pressure will increase the overall volume and hence decreases $\frac{n_g}{V}$. The reaction will favor that side where number of gaseous moles are increasing. Here , they are increasing in the forward side ( from 1 to 2). Forward reaction is favoured.

Option D: Increasing the volume will have the similar effect of addition of inert gas at constant pressure as discussed above in option c.
So, Option C and D are correct.