Problem 91 - A Complete Resource Book in Chemistry for JEE Main

Question

In which of the following reactions, the concentration of product is higher than the concentration of reactant at equilibrium? \(=\) equilibrium constant \()\) (a) \(\mathrm{A} \rightleftharpoons \mathrm{B} ; \mathrm{K}=0.001\) (b) \(\mathrm{M} \rightleftharpoons \mathrm{N} ; \mathrm{K}=10\) (c) \(\mathrm{X} \rightleftharpoons \mathrm{Y} ; \mathrm{K}=0.005\) (d) \(\mathrm{R} \rightleftharpoons \mathrm{P} ; \mathrm{K}=0.01\)

Step-by-Step Solution

Answer

In reaction (b), the concentration of products is higher than reactants at equilibrium.

Step 1: Understanding Equilibrium Constant (K)

The equilibrium constant, denoted as \( K \), is the ratio of the concentrations of products to reactants at equilibrium. A higher \( K \) value indicates a greater concentration of products relative to reactants, while a lower \( K \) value indicates the opposite.

Step 2: Comparing Equilibrium Constants

Look at the given equilibrium constants for each reaction:(a) \( K = 0.001 \)(b) \( K = 10 \)(c) \( K = 0.005 \)(d) \( K = 0.01 \)Here, the equilibrium constant for reaction (b), \( K = 10 \), is the largest among the given choices.

Step 3: Concluding with the Highest Concentration of Products

Since reaction (b) \( M \rightleftharpoons N \) has the highest equilibrium constant \( K = 10 \), the concentration of products (\( N \)) is higher than that of reactants (\( M \)) at equilibrium. Thus, reaction (b) will have more products compared to reactants.

Key Concepts

Chemical Equilibrium

In a chemical reaction, the state where the concentrations of reactants and products remain constant over time is known as chemical equilibrium. This does not mean that the substances have stopped reacting. Instead, they continue to react at the same rate in both the forward and reverse directions.
Therefore, chemical equilibrium is dynamic in nature. At this point, both the forward and reverse reactions occur simultaneously, leading to no net change in the concentration of reactants and products.
Achieving equilibrium depends on the specific conditions such as temperature and pressure and does not favor either side of the reaction inherently without specific influencers.

• It involves a balance between forward and reverse reactions.
• Equilibrium does not imply equal concentrations of reactants and products.
• External factors (like temperature) can shift the balance between reactants and products.

Concentration of Products and Reactants

When discussing chemical equilibria, the concentration of products and reactants is crucial. At equilibrium, the actual concentrations of these species depend on the equilibrium constant, denoted as \( K \).
The concentration ratio is derived from the reaction quotient. Reactants and products each have a specific concentration represented in moles per liter \( \text{mol/L} \).
The equilibrium constant \( K \) provides insight into the position of equilibrium:

• If \( K \) is greater than 1, products are favored, meaning their concentrations are higher at equilibrium.
• If \( K \) is less than 1, the reactants are favored, so their concentrations will be higher.
• The actual concentration values need conditions such as temperature for accurate representation.

Equilibrium Reactions

Reactions that reach a state of balance between opposing processes are termed as equilibrium reactions. In these, neither the reactants nor the products are entirely converted.
The behavior of equilibrium reactions is inclined towards achieving minimal energy and maximum randomness. The driving force behind this state is a system's natural tendency to move towards equilibrium under closed conditions.
To determine the direction of the reaction at equilibrium, the equilibrium constant \( K \) is used as a measure.

• Equilibrium reactions show a dynamic involvement of species without an apparent change in concentrations over time.
• A large \( K \) value indicates the products are favored at equilibrium.
• In contrast, a small \( K \) value implies the reactants are favored.
• External changes, such as pressure or temperature, can influence the equilibrium state, causing shifts according to Le Chatelier's Principle.