Question

Suppose the reaction system $$2 \mathrm{NO}(g)+\mathrm{O}_{2}(g) \rightleftharpoons 2 \mathrm{NO}_{2}(g)$$ has already reached equilibrium. Predict the effect of each of the following changes on the position of the equilibrium. Tell whether the equilibrium will shift to the right, will shift to the left, or will not be affected. a. Additional oxygen is injected into the system. b. \(\mathrm{NO}_{2}\) is removed from the reaction vessel. c. 1.0 mol of helium is injected into the system.

Short answer

a. The equilibrium will shift to the right due to the increased O₂ concentration, according to Le Châtelier's principle. b. The equilibrium will shift to the right to produce more NO₂ molecules as they are removed from the system. c. Injecting helium will not affect the equilibrium position, as it does not directly impact the reactants or products' concentrations.

Step-by-step solution

a. Additional oxygen is injected into the system.

According to Le Châtelier's principle, when we increase the concentration of a reactant (in this case, O₂), the reaction will shift in the direction that consumes the added reactant. Thus, the equilibrium will shift to the right, producing more NO₂ molecules to consume the added O₂.

b. NO₂ is removed from the reaction vessel.

When we remove a product (in this case, NO₂) from the system, Le Châtelier's principle tells us that the reaction will shift in the direction that produces the removed product to counteract the stress. So, the equilibrium will shift to the right to produce more NO₂ molecules to replace the removed ones.

c. 1.0 mol of helium is injected into the system.

Adding helium (He) does not directly affect the concentration of any of the reactants or products in the reaction. Therefore, injecting helium into the system will have no impact on the position of the equilibrium, and it will not shift to the right or left.

Key concepts

Chemical Equilibrium

Chemical equilibrium is a state in a chemical reaction where the rate of the forward reaction equals the rate of the reverse reaction. This means that the concentrations of reactants and products remain constant over time. Reaching equilibrium does not imply that the reactants and products are present in equal amounts, but rather that their rates of conversion are balanced.
In the reaction involving \[2 \text{NO}(g) + \text{O}_{2}(g) \rightleftharpoons 2 \text{NO}_{2}(g)\]at equilibrium, the rate at which nitrogen dioxide (\(\text{NO}_2\)) is formed is the same as the rate at which it decomposes back into nitrogen monoxide (\(\text{NO}\)) and oxygen (\(\text{O}_2\)). This balance is sensitive to changes, as Le Châtelier's principle predicts how the system will respond to disturbances such as changes in concentration, temperature, or pressure.

Reaction Shift

When a chemical system at equilibrium experiences a change in conditions, a reaction shift may occur. This shift is the system's way of counteracting the disturbance to restore equilibrium. Le Châtelier's principle is a useful guide for predicting the direction of this shift.
For example, if you inject additional oxygen into the equilibrium system of \[2 \text{NO}(g) + \text{O}_{2}(g) \rightleftharpoons 2 \text{NO}_{2}(g)\],the reaction will shift to the right. This means that more \(\text{NO}_2\) will be produced because the system seeks to reduce the increased concentration of \(\text{O}_2\).
If instead, \(\text{NO}_2\) is removed, the reaction also shifts to the right. The removal of \(\text{NO}_2\) decreases its concentration, prompting the system to produce more \(\text{NO}_2\) to reclaim the disturbed balance.

NO2 Production

In chemical equilibrium involving \(\text{NO}_2\), its production is a key aspect of the reaction's dynamics. The equilibrium reaction \[2 \text{NO}(g) + \text{O}_{2}(g) \rightleftharpoons 2 \text{NO}_{2}(g)\],relies heavily on the amounts of reactants and products present.
Whenever a change occurs, such as adding more \(\text{O}_2\) or removing \(\text{NO}_2\), the system responds by shifting its equilibrium position.

• Adding more \(\text{O}_2\) results in more \(\text{NO}_2\) being formed as the system shifts to the right.
• Removing \(\text{NO}_2\) drives the system to also shift to the right, further increasing \(\text{NO}_2\) production to compensate for its reduction.

Effect of Concentration Change

The effect of concentration change on a chemical equilibrium can dramatically influence the direction of the reaction shift. Changes in concentration alter the equilibrium position to minimize the effect of the change.
According to Le Châtelier's principle:

• Increasing the concentration of a reactant or product pushes the system to shift away from the added component to lower its concentration.
• Decreasing the concentration of a reactant or product results in the system shifting towards the removed component to increase its concentration.

For the reaction \[2 \text{NO}(g) + \text{O}_{2}(g) \rightleftharpoons 2 \text{NO}_{2}(g)\],the addition of \(\text{O}_2\) causes the system to shift right, boosting \(\text{NO}_2\) production. Removing \(\text{NO}_2\) also leads to a rightward shift, further increasing \(\text{NO}_2\) synthesis until the equilibrium re-establishes.