Question

Consider the following equilibrium system$;{SO}_2\left(g\right)+\frac{1}{2}{O}_2\left(g\right)\rightleftharpoons {SO}_3\left(g\right);$ set up in a cylinder fitted with a piston. Some inert gas is added and the piston is moved outwards to keep the total gaseous pressure constant. Predict which of the following is true?

• A. Addition of inert gas does not affect the equilibrium.
• B. Less ${SO}_3\left(g\right)$ is produced.
• C. More ${SO}_3\left(g\right)$ is produced.
• D. The system moves to new equilibrium position which cannot be predicted theoretically.

Answer 1

The correct option is B Less ${SO}_3\left(g\right)$ is produced.

${SO}_{2\left(g\right)}+\frac{1}{2}{O}_{2\left(g\right)}\rightleftharpoons {SO}_{3\left(g\right)}$

The number of moles of reactants$=1+\frac{1}{2}=\frac{3}{2}$

The number of moles of product $=1$

According to Le-Chatelier's principle, if inert gas is added at constant pressure, it will increase the volume of the system. Therefore, the quilibrium will shift in a direction in which there is an increase in the number of moles of gases.

$\therefore$ Here, the quilibrium will shift backwards.

$\therefore$ Less ${SO}_{3\left(g\right)}$ is less produced.

Answer:$\left(B\right)$ Less ${SO}_{3\left(g\right)}$ is produced.