Predicting Equilibrium Shifts with Pressure: Worked Examples

🧪 Quick Study Guide

• ⚖️ Le Chatelier's Principle states that if a change of condition is applied to a system in equilibrium, the system will shift in a direction that relieves the stress.
• 💨 Pressure changes primarily affect gaseous equilibria.
• 📈 Increasing pressure favors the side with fewer moles of gas.
• 📉 Decreasing pressure favors the side with more moles of gas.
• 🌡️ If the number of moles of gas is the same on both sides, pressure changes have minimal effect.
• 🧮 Use the balanced chemical equation to determine the number of moles of gas on each side.
• ⚗️ Inert gases added to a system at constant volume do not affect the equilibrium.

Practice Quiz

1. Which of the following changes will shift the equilibrium of the reaction $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$ to the right?
   1. Increasing the pressure.
   2. Decreasing the pressure.
   3. Adding an inert gas at constant volume.
   4. Increasing the temperature.
2. Consider the reaction $2SO_2(g) + O_2(g) \rightleftharpoons 2SO_3(g)$. What happens to the equilibrium if the pressure is increased?
   1. Shifts to the right.
   2. Shifts to the left.
   3. No change.
   4. Equilibrium constant changes.
3. For the reaction $H_2(g) + I_2(g) \rightleftharpoons 2HI(g)$, how will increasing the pressure affect the equilibrium?
   1. Shifts to the right.
   2. Shifts to the left.
   3. No change.
   4. The reaction rate decreases.
4. What will happen to the equilibrium of the reaction $CO(g) + Cl_2(g) \rightleftharpoons COCl_2(g)$ if the volume of the container is decreased?
   1. Shifts to the right.
   2. Shifts to the left.
   3. No change.
   4. The equilibrium constant decreases.
5. Consider the reaction $PCl_5(g) \rightleftharpoons PCl_3(g) + Cl_2(g)$. What happens to the equilibrium if the pressure is decreased?
   1. Shifts to the right.
   2. Shifts to the left.
   3. No change.
   4. The reaction rate increases.
6. In which of the following reactions will increasing the pressure NOT affect the equilibrium position?
   1. $2NO_2(g) \rightleftharpoons N_2O_4(g)$
   2. $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$
   3. $H_2(g) + Cl_2(g) \rightleftharpoons 2HCl(g)$
   4. $2SO_3(g) \rightleftharpoons 2SO_2(g) + O_2(g)$
7. For the reaction $C(s) + O_2(g) \rightleftharpoons CO_2(g)$, how does increasing the pressure affect the equilibrium?
   1. Shifts to the right.
   2. Shifts to the left.
   3. No change.
   4. The equilibrium constant increases.