The Question is from neet-chemistry chemical-equilibrium , and it was created by the author A.RAMA NAGESWARARAO

Question

A sealed container holds an equilibrium mixture of $N_2O_4(g)$ (colorless) and $NO_2(g)$ (brown).  The forward reaction is endothermic.  Which of the following changes will NOT result in an increase in the intensity of the brown color within the container?

A.RAMA NAGESWARARAO · Accepted Answer

## CORE INFORMATION
✓ **Answer**: 3
## CONCEPT FRAMEWORK
 **Primary Concept**: Le Chatelier's Principle and Equilibrium Shifts
 **Related Topics**: Chemical Equilibrium, Endothermic Reactions, Gas Laws
 **Prerequisites**: Understanding of equilibrium constants, reaction quotient, and the effect of temperature and pressure on equilibrium.
## SOLUTION PATHWAY
**Given Information**:
  $N_2O_4(g) ightleftharpoons 2NO_2(g)$ (endothermic)
  $NO_2$ is brown, $N_2O_4$ is colorless.
  The intensity of brown color is directly proportional to the concentration of $NO_2$.
**Method & Steps**:
 1. Analyze the effect of each change on the equilibrium using Le Chatelier's principle.
  Reasoning: 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.
 2. Determine which change does not favor the forward reaction (producing more $NO_2$).
  Working:
  A. Increasing temperature: Since the forward reaction is endothermic (absorbs heat), increasing the temperature shifts the equilibrium to the right, increasing $[NO_2]$ and thus the brown color intensity.
  B. Decreasing pressure: Decreasing the pressure favors the side with more gas moles.  The forward reaction produces 2 moles of gas ($NO_2$) from 1 mole ($N_2O_4$), so decreasing pressure shifts the equilibrium to the right, increasing $[NO_2]$.
  C. Adding a catalyst: A catalyst speeds up both the forward and reverse reactions equally, it does not affect the equilibrium position. Therefore, the concentration of $NO_2$ remains unchanged.
  D. Adding an inert gas at constant volume: Adding an inert gas at constant volume increases the total pressure but does not change the partial pressures of the reactants and products.  Therefore, there is no shift in equilibrium.
 3. Identify the change that does NOT increase the intensity of the brown color.
  Result: Adding a catalyst (option 3) will not increase the intensity of the brown color.
  Verification:  The other options all increase the concentration of $NO_2$ by shifting the equilibrium towards the products.
 ## OPTION ANALYSIS
A ✓: Increasing temperature shifts the equilibrium to the right, increasing $[NO_2]$ and the brown color.
B :x: Decreasing pressure shifts the equilibrium to the right, increasing $[NO_2]$ and the brown color.
C :x: Adding a catalyst does not affect the equilibrium position, so $[NO_2]$ remains unchanged.
D :x: Adding an inert gas at constant volume does not change the partial pressures, so the equilibrium position is unaffected.
 ## LEARNING AIDS
 **Common Mistakes**:
  1.Confusing endothermic and exothermic reactions: Remember that increasing temperature favors endothermic reactions.
  2.Misunderstanding the effect of pressure changes:  Pressure changes only affect gaseous equilibria and favor the side with fewer gas molecules when pressure increases and more gas molecules when pressure decreases.
 **Quick Tips**:
  1.Use ICE (Initial, Change, Equilibrium) tables to solve equilibrium problems.
  2.Remember Le Chatelier's principle as a guiding rule for predicting equilibrium shifts.

A.RAMA NAGESWARARAO · Answer

Increasing the temperature of the container

A.RAMA NAGESWARARAO · Answer

Decreasing the pressure within the container

A.RAMA NAGESWARARAO · Answer

The correct Option is "Adding a catalyst while keeping temperature constant"

A.RAMA NAGESWARARAO · Answer

Adding an inert gas at constant volume

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