Question

Consider the following reaction at equilibrium. If some amount of argon gas is added to the reaction mixture at constant pressure then

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

Answer 1

Addition of inert gas at equilibrium:

• In the reaction ${\mathrm{PCl}}_5\left(\mathrm{g}\right)\rightleftharpoons {\mathrm{PCl}}_3\left(\mathrm{g}\right)+{\mathrm{Cl}}_2\left(\mathrm{g}\right)$, 1 mol of ${\mathrm{PCl}}_5$ produces 1 mol of ${\mathrm{PCl}}_3$ and ${\mathrm{Cl}}_2$ gas.
• When inert gas is added at constant pressure the total volume increases and the equilibrium is shifted toward the side where there is an increase in the number of moles.
• In the above reaction, the number of moles of reactant and product is equal so the equilibrium will not shift in any direction.

So, the addition of Argon gas will have no effect on the reaction equilibrium.