If there is no change in volume in a gaseous reaction, the pressure will

Analysis

This question tests your understanding of Le Chatelier’s Principle as it applies to gaseous equilibrium reactions, specifically focusing on the effect of pressure changes.

Concept Explanation

Le Chatelier’s Principle states that if a dynamic equilibrium is disturbed by changing the conditions (like pressure, temperature, or concentration), the position of equilibrium shifts to counteract the change.

When dealing with pressure in gaseous reactions:

1. Pressure changes only affect the equilibrium position if there is a change in the number of moles of gas between the reactants and the products.
2. If the total number of moles of gaseous reactants equals the total number of moles of gaseous products (i.e., $\Delta n = 0$), the volume remains constant during the reaction.
3. In such cases, increasing or decreasing the pressure will affect both sides of the equation equally, meaning there is no net shift in the equilibrium position.

Step-by-Step Solution

1. Identify the condition: The question specifies "no change in volume" in the reaction. This mathematically means the sum of the stoichiometric coefficients of the gaseous reactants equals the sum of the stoichiometric coefficients of the gaseous products.
2. Apply the principle: Since the number of moles of gas on both sides is the same, changing the pressure does not favor either the forward or the backward reaction.
3. Conclusion: Because the pressure change exerts an equal force on both sides of the equilibrium, the system remains balanced. Therefore, pressure has no effect on the equilibrium position.

Exam Tip

Whenever you see a question about pressure and equilibrium, quickly write out the balanced equation and count the moles of gas on both sides.

• If moles are different, pressure change shifts the equilibrium.
• If moles are the same, pressure change has no effect.
• Memory trick: Think of it like a seesaw with equal weights on both sides; moving the fulcrum (pressure) doesn't tip the balance!