Question

For the equilibrium reaction, $PCl_5(g) + Heat \rightleftharpoons PCl_3(g) + Cl_2(g)$, the favourable condition required to maximise the yield of $PCl_5$ is

• A. Decrease in pressure
• B. Increase in temperature
• C. Addition of inert gas at constant volume
• D. Decrease in temperature and increase in pressure

Answer 1

Answer: (D)

Decrease in temperature and increase in pressure

Answer 2

To maximize $PCl_5$ yield, the equilibrium $PCl_5(g) + Heat \rightleftharpoons PCl_3(g) + Cl_2(g)$ must shift left.

1. Temperature: The forward reaction is endothermic. Decreasing temperature favors the exothermic reverse reaction, increasing $PCl_5$.

2. Pressure: Reactants have 1 mole of gas, products have 2 moles. Increasing pressure favors the side with fewer moles of gas (reactants), increasing $PCl_5$.

Thus, decreasing temperature and increasing pressure are favorable.