Скачать или смотреть In the following system, PCl5(g) ⇌ PCl3(g) + Cl2(g) at equilibrium, upon addition of xenon gas at co

1. Question Statement:
In the following system,
PCl₅(g) ⇌ PCl₃(g) + Cl₂(g) at equilibrium, upon addition of xenon gas at constant Temperature (T) and Pressure (p), the concentration of:
(1) PCl₅ will increase
(2) Cl₂ will decrease
(3) PCl₅, PCl₃ & Cl₂ remain constant
(4) PCl₃ will increase

2. Theory and Concepts:
Le Chatelier's Principle, equilibrium shift, pressure-volume relationships, inert gas effect at constant pressure—these are the most important keywords for this problem. This question deals with chemical equilibrium, where the reversible reaction PCl₅ ⇌ PCl₃ + Cl₂ is already at equilibrium. According to Le Chatelier's Principle, if a system at equilibrium is disturbed, it will try to counteract the disturbance and restore a new equilibrium position. The addition of an inert gas like xenon (Xe) can affect equilibrium, but the effect depends on whether pressure or volume is kept constant.

When inert gas is added at constant volume, it increases the total pressure but does not change the partial pressures of the reactants and products because the mole fraction remains the same. Hence, under constant volume, equilibrium usually remains unaffected. However, when inert gas is added at constant pressure, the system needs to expand to keep the pressure the same. This expansion leads to an increase in volume, causing a decrease in the partial pressures (or concentrations) of all gases present in the reaction mixture.

For reactions involving gases, this change in volume at constant pressure becomes significant. Since the reaction PCl₅ ⇌ PCl₃ + Cl₂ involves a change in the number of moles of gas (1 mole of PCl₅ produces 2 moles of products), a decrease in concentration due to expansion will shift the equilibrium towards the side with more moles of gas—here, the forward direction (PCl₅ decomposes more). This is a classic application of the law of mass action and equilibrium response to concentration changes. Such concepts are frequently tested in competitive exams like JEE and NEET.