Le Châtelier's principle Knowledge-Based Practice

Questions

1. 1.

   The endothermic decomposition reaction $\text{CaCO}_3(s) \rightleftharpoons \text{CaO}(s) + \text{CO}_2(g)$ ($\Delta H^\circ > 0$) has reached dynamic equilibrium in a closed rigid container. Which of the following changes will increase the total mass of $\text{CaO}(s)$ present at equilibrium?

   • A) Adding more solid calcium carbonate, $\text{CaCO}_3(s)$, to the vessel at constant temperature
   • B) Decreasing the volume of the reaction container at constant temperature
   • C) Injecting additional carbon dioxide gas, $\text{CO}_2(g)$, into the vessel at constant temperature
   • D) Increasing the temperature of the reaction vessel at constant volume
2. 2.

   For the gas-phase reaction $\text{H}_2(g) + \text{I}_2(g) \rightleftharpoons 2\text{HI}(g)$ at dynamic equilibrium in a closed vessel at constant temperature, which statement correctly describes the effect of halving the volume of the container?

   • A) The equilibrium shifts toward the products because the total pressure increases.
   • B) The equilibrium position does not shift because the number of moles of gas is equal on both sides.
   • C) The equilibrium constant $K_c$ increases because the concentrations of all species increase.
   • D) The equilibrium shifts toward the reactants to counteract the increase in total pressure.
3. 3.

   The reversible reaction $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$ ($\Delta H < 0$) has reached dynamic equilibrium in a closed container. Which of the following changes will shift the equilibrium position toward the reactants without altering the value of the equilibrium constant, $K_c$?

   • A) Increasing the temperature of the system
   • B) Decreasing the volume of the container at constant temperature
   • C) Adding more $\text{H}_2(g)$ to the container at constant volume
   • D) Increasing the volume of the container at constant temperature
4. 4.

   The endothermic gas-phase reaction $\text{N}_2\text{O}_4(g) \rightleftharpoons 2\text{NO}_2(g)$ is established at dynamic equilibrium inside a closed vessel. Which of the following changes will shift the equilibrium position to the right and also increase the value of the equilibrium constant, $K$?

   • A) Decreasing the container volume at constant temperature
   • B) Increasing the temperature of the system at constant volume
   • C) Increasing the container volume at constant temperature
   • D) Adding an inert gas to the vessel at constant volume
5. 5.

   Consider the reversible reaction at dynamic equilibrium: $2\text{SO}_2(g) + \text{O}_2(g) \rightleftharpoons 2\text{SO}_3(g)$ with $\Delta H < 0$. Which change will shift the equilibrium position toward the products?

   • A) Increasing the temperature of the reaction vessel
   • B) Decreasing the total pressure by expanding the container volume
   • C) Removing sulfur trioxide gas continuously from the container
   • D) Adding a solid catalyst to the equilibrium mixture

Answers and step-by-step solutions appear after you finish the test.