Problem 76 - Chemistry: An Atoms-Focused Approach

Question

How will the changes listed affect the position of the following equilibrium? $$ 2 \mathrm{NO}_{2}(\mathrm{g}) \rightleftharpoons \mathrm{NO}(g)+\mathrm{NO}_{3}(\mathrm{g}) $$ a. The concentration of \(\mathrm{NO}\) is increased. b. The concentration of \(\mathrm{NO}_{2}\) is increased. c. The volume of the system is allowed to cxpand to 5 times its initial value.

Step-by-Step Solution

Answer

a. The concentration of NO is increased. b. The concentration of NO₂ is increased. c. The volume of the system is expanded to 5 times its initial value. Answer: a. The equilibrium will shift to the left, increasing the concentration of NO₂. b. The equilibrium will shift to the right, increasing the concentrations of NO and NO₃. c. The equilibrium will shift to the left, increasing the concentration of NO₂ and decreasing the concentrations of NO and NO₃.

Step 1: a. Increasing the concentration of \(\mathrm{NO}\)

According to Le Chatelier's principle, increasing the concentration of \(\mathrm{NO}\) will shift the equilibrium to the left to counteract the change. This means that more \(\mathrm{NO}_{2}\) will be produced, leading to a decrease in the concentration of \(\mathrm{NO}\) and an increase in the concentration of \(\mathrm{NO}_{2}\) until a new equilibrium is established.

Step 2: b. Increasing the concentration of \(\mathrm{NO}_{2}\)

Similarly, increasing the concentration of \(\mathrm{NO}_{2}\) will shift the equilibrium to the right, following Le Chatelier's principle. As a result, more \(\mathrm{NO}\) and \(\mathrm{NO}_{3}\) will be produced, and the concentration of \(\mathrm{NO}_{2}\) will decrease until a new equilibrium position is reached.

Step 3: c. Expanding the volume of the system

When the volume of the system is allowed to expand, the pressure in the system decreases. According to Le Chatelier's principle, the equilibrium will shift towards the side with a higher number of moles of gas to counteract the decrease in pressure. In this case, we have 2 moles of \(\mathrm{NO}_{2}\) on the left-hand side of the reaction and 1 mole of \(\mathrm{NO}\) and 1 mole of \(\mathrm{NO}_{3}\) on the right-hand side, making a total of 2 moles of gas on the right. Since the left-hand side has a higher number of moles of gas, the equilibrium will shift to the left, leading to an increase in the concentration of \(\mathrm{NO}_{2}\) and a decrease in the concentration of \(\mathrm{NO}\) and \(\mathrm{NO}_{3}\) until a new equilibrium position is reached.

Key Concepts

Equilibrium Shift

In the world of chemistry, an equilibrium shift occurs when a system at equilibrium is disturbed by changing conditions such as concentration, pressure, or temperature. Le Chatelier's Principle offers a way to predict how the system will respond to these changes. It states that if a dynamic equilibrium is subjected to change, the system will adjust itself to counteract the effect of the disturbance and restore a new equilibrium.
When a change is imposed, the equilibrium will shift in the direction that relieves the stress:

• If a substance's concentration is increased, the equilibrium will shift to consume the added substance.
• Decreasing a substance’s concentration will shift the equilibrium to produce more of that substance.
• Changes in pressure and volume will affect gaseous equilibria by favoring the side of the reaction with fewer or more moles of gas, respectively.

Let's consider an example: increasing the concentration of NO leads the equilibrium to shift left, promoting the formation of more NO₂ to balance the increased NO. This dynamic adjustment showcases the system's inherent push to reach stability once again.

Chemical Equilibrium

Chemical equilibrium refers to the state of a reversible reaction where the rates of the forward and reverse reactions are equal, meaning the concentrations of reactants and products remain constant over time. It is an essential concept in understanding how reactions behave under different conditions, allowing scientists to predict the outcome of changes in the system.
Here’s a snapshot of what happens at chemical equilibrium:

• The reaction does not stop; molecules continue to react, but there is no net change in the concentration of reactants and products.
• The equilibrium can be reached from either direction of the reaction, depending on the initial concentrations.

When the system reaches equilibrium, it can be described by an equilibrium constant, symbolized as K, which is a ratio of the concentrations of products to reactants, each raised to the power of their coefficients in the balanced chemical equation. For example, the reaction between NO₂ and NO can establish equilibrium, allowing chemists to alter conditions, such as concentration or pressure, and evaluate the shifts and outcomes predicted by Le Chatelier's principle.

Reaction Dynamics

Understanding reaction dynamics is key to deciphering how and why reactions occur at the microscopic level. This involves exploring how the factors like concentration, temperature, and catalysts affect the speed of reactions and how equilibrium responds to these modifications.
Key aspects of reaction dynamics include:

• **Reaction Rate**: This is the speed at which reactants are converted into products. It can be influenced by changes in concentration, surface area, and presence of catalysts.
• **Equilibrium Adjustments**: Based on Le Chatelier's principle, changes in concentrations or pressure dynamically affect the position of equilibrium. Increasing the pressure, for example, can shift the equilibrium toward the side with fewer gaseous moles.

For instance, in the NO₂ and NO reaction: altering conditions such as volume will invoke an equilibrium shift due to reaction dynamics seeking to reestablish equilibrium. By examining these dynamics, chemists can infer the behavior of the reaction under new conditions, fostering a deeper understanding of equilibrium processes.