Problem 61 - A Complete Resource Book in Chemistry for JEE Main

Question

The equilibrium constant of a reaction is 300 . If the volume of reaction flask is tripled, the equilibrium constant is (a) 300 (b) 600 (c) 900 (d) 100

Step-by-Step Solution

Answer

The equilibrium constant remains 300, choice (a).

Step 1: Understanding the Equilibrium Constant

The equilibrium constant (K) of a reaction, typically denoted as K_c for concentration-based equilibria, is a measure of the extent to which reactants are converted into products at equilibrium. It is a constant value at a given temperature that doesn't change with changes in pressure, volume, or concentration.

Step 2: Analyzing the Effect of Volume Change

The equilibrium constant is independent of the volume of the reaction flask. Changing the volume might affect the concentrations of reactants and products temporarily, but the equilibrium position will adjust to maintain the same equilibrium constant. Thus, the volume change does not alter the value of the equilibrium constant K.

Step 3: Concluding the Problem

Since the equilibrium constant remains the same irrespective of changes in volume, the answer to what the equilibrium constant becomes when the volume is tripled is still the same value as initially given, 300.

Key Concepts

Equilibrium Constant

In chemical reactions, the equilibrium constant, often represented as \( K_c \) for systems based on concentrations, provides us with a snapshot of a system's state at equilibrium. It is a crucial number because it tells us the ratio of products to reactants under equilibrium conditions. The equilibrium constant is calculated using the formula: \[K_c = \frac{[ ext{Products}]}{[ ext{Reactants}]}\]where brackets denote concentrations. It's important to remember that \( K_c \) is specific for a reaction at a constant temperature. This is because chemical equilibrium is dynamic, meaning molecules of reactants and products are constantly converting from one to another, yet the ratio given by \( K_c \) stays steady. Even when pressures or concentrations change due to alterations in volume, the constant itself remains unaffected.

Le Chatelier's Principle

Le Chatelier's principle helps to predict how a system in equilibrium reacts to external changes. Simply put, if a dynamic equilibrium system experiences a disturbance such as changes in concentration, temperature, or volume, the system will adjust itself to counteract the change and restore a new equilibrium. - When concentration changes: Adding more reactants or products will shift the equilibrium to oppose the change. For example, adding a reactant shifts the equilibrium towards the formation of more products. - When temperature changes: For exothermic reactions, increasing the temperature shifts equilibrium towards the reactants, whereas for endothermic reactions, it shifts towards the products. - Volume and pressure changes: These affect reactions involving gases, where increasing volume (or decreasing pressure) shifts the equilibrium towards the side with more gas molecules and vice versa. Understanding Le Chatelier's principle is key to predicting how a reaction will behave under various conditions.

Volume Changes in Equilibrium

In reactions where gases are involved, volume changes can drastically affect the concentration of reactants and products. However, it's essential to remember that the equilibrium constant, \( K_c \), remains unaffected by these changes.When the volume of a system increases, this can lead to a decrease in pressure. According to Le Chatelier's principle, the system will adjust to minimize this change. This often results in the equilibrium shifting towards the side with more molecules of gas.However, because the equilibrium constant is dependent only on temperature, it remains the same, regardless of how much the volume is altered. In the provided scenario with a tripling of volume, there might be a shift in equilibrium position, but \( K_c \) stays unchanged at 300. So, while the concentrations of individual species might change temporarily, the overall ratio dictated by \( K_c \) remains constant.