Question

Consider this equilibrium system: $$ \mathrm{CO}(g)+\mathrm{Fe}_{3} \mathrm{O}_{4}(s) \rightleftharpoons \mathrm{CO}_{2}(g)+3 \mathrm{FeO}(s) $$ How does the equilibrium position shift as a result of each of the following disturbances? (a) CO is added. (b) \(\mathrm{CO}_{2}\) is removed by adding solid \(\mathrm{NaOH}\). (c) Additional \(\mathrm{Fe}_{3} \mathrm{O}_{4}(s)\) is added to the system. (d) Dry ice is added at constant temperature.

Short answer

(a) Right (b) Right (c) No effect (d) Left

Step-by-step solution

- Understand the Equilibrium Reaction

The reaction is given as: \[ \text{CO}(g) + \text{Fe}_{3}\text{O}_{4}(s) \rightleftharpoons \text{CO}_{2}(g) + 3 \text{FeO}(s) \] This reaction involves both gaseous and solid species. Understand Le Chatelier's principle, which states that the system will adjust to counteract the disturbance.

- Analyze the Effect of Adding CO

Adding CO increases the concentration of one of the reactants. According to Le Chatelier's principle, the system will shift to reduce this disturbance by shifting the equilibrium to the right, producing more products (i.e., CO2 and FeO).

- Analyze the Effect of Removing CO2 by Adding NaOH

Adding solid NaOH will react with CO2 to form Na2CO3, effectively removing CO2 from the system. The system will respond by shifting the equilibrium to the right to produce more CO2.

- Analyze the Effect of Adding More Fe3O4

Fe3O4 is a solid and its addition does not affect the equilibrium concentrations of the gases. Therefore, adding more Fe3O4 has no effect on the equilibrium position.

- Analyze the Effect of Adding Dry Ice

Dry ice is solid CO2, and adding it will increase the concentration of CO2 gas as it sublimes. According to Le Chatelier's principle, the equilibrium will shift to the left to reduce the increased concentration of CO2, resulting in the formation of more CO and Fe3O4.

Key concepts

Le Chatelier's Principle

Le Chatelier's principle is a cornerstone concept in understanding chemical equilibria. It states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium moves to counteract the change. This principle helps predict the direction of the equilibrium shift when the system experiences disturbances like changes in concentration, temperature, or pressure.
When a reactant or product is added to or removed from a system in equilibrium, the system will shift in the direction that attempts to restore the balance. For example, if a reactant is added, the equilibrium will shift to the right to form more products. Conversely, if a product is removed, the equilibrium will shift to the right to replace the lost product.

Effect of Concentration Changes

Concentration changes are a common way to disturb chemical equilibrium. In our example reaction:
\[ \text{CO}(g) + \text{Fe}_3\text{O}_4(s) \rightleftharpoons \text{CO}_2(g) + 3\text{FeO}(s) \]
when CO is added to the system, the concentration of the reactant increases. According to Le Chatelier's principle, the system will shift to the right, producing more CO2 and FeO to balance the increased concentration of CO. Conversely, removing CO2 by adding solid NaOH, which reacts with CO2 to form Na2CO3, results in a decreased concentration of CO2. The system shifts to the right to produce more CO2, achieving a new equilibrium state.

Gaseous and Solid Species in Equilibrium

In chemical equilibrium, gaseous and solid species behave differently. Gases are highly responsive to changes in concentration, pressure, and volume. However, solids, because of their constant concentration, do not affect the equilibrium position when their amount is changed.
In our reaction example, adding more Fe3O4, which is a solid, does not affect the equilibrium position. This is because solids have a fixed concentration under standard conditions, and their addition does not alter the equilibrium concentrations of the gaseous species. Thus, the equilibrium remains unchanged, highlighting a unique aspect of solid species in chemical equilibrium.

Chemical Equilibrium Disturbances

Various disturbances can affect the chemical equilibrium of a system. Some common disturbances include changes in concentration, temperature, and pressure. An example from our exercise is the addition of dry ice, which is solid CO2.
When dry ice is added to the system, it sublimates to form CO2 gas, thus increasing the concentration of CO2 in our reaction:
\[ \text{CO}(g) + \text{Fe}_3\text{O}_4(s) \rightleftharpoons \text{CO}_2(g) + 3\text{FeO}(s) \]
According to Le Chatelier's principle, the system will shift to the left to reduce the increased concentration of CO2. This results in the formation of more CO and Fe3O4. Understanding these disturbances can help predict how equilibrium will adjust in response to various changes, aiding in the control and manipulation of chemical reactions in practical applications.