Problem 28 - A Complete Resource Book in Chemistry for JEE Main

Question

Which of the following favours the backward reaction in a chemical equilibrium? (a) decreasing the concentration of one of the reactants (b) increasing the concentration of one of the reactants (c) increasing the concentration of one or more of the products (d) removal of at least one of the products at regular intervals

Step-by-Step Solution

Answer

Increasing product concentration favors the backward reaction.

Step 1: Analyze the effect of reactant concentration decrease

According to Le Chatelier's principle, if the concentration of a reactant in a chemical equilibrium is decreased, the system will shift to the left to produce more reactants. This favors the backward reaction.

Step 2: Examine the impact of reactant concentration increase

Increasing the concentration of a reactant typically shifts the equilibrium towards the forward reaction, producing more products. Thus, increasing the concentration of a reactant doesn't favor the backward reaction.

Step 3: Consider the effect of increasing product concentration

If the concentration of products is increased, Le Chatelier's principle suggests that the equilibrium will shift to the left to consume these products and form more reactants. This favors the backward reaction.

Step 4: Impact of product removal

Regularly removing one or more products from the reaction shifts the equilibrium towards the forward direction, as the system works to replace the removed products. This does not favor the backward reaction.

Key Concepts

Le Chatelier's Principle

Le Chatelier's Principle is a fundamental concept in understanding chemical equilibrium. It was formulated by the French chemist Henry Louis Le Chatelier. The principle explains how a chemical system at equilibrium responds to changes in concentration, temperature, pressure, or volume.
When a system at equilibrium experiences a change or stress, it will adjust itself to counteract that change. This adjustment re-establishes equilibrium. It's a natural way for the system to maintain balance.
Key points of Le Chatelier's Principle:

• Introducing more reactants shifts the equilibrium towards products (forward reaction).
• Increasing products' concentration shifts the equilibrium towards reactants (backward reaction).
• Reactions tend to shift in a way that reduces the change applied to the system.

Thus, Le Chatelier’s Principle helps predict the direction in which a reaction will shift when a change is applied.

Backward Reaction

Backward Reaction refers to the reverse process of a chemical reaction. In any chemical equilibrium, there are both forward and backward reactions competing against each other. When we refer to the backward reaction, we mean the transformation of products back into reactants.
In the context of Le Chatelier's Principle, certain changes can favor the backward reaction, making the system produce more reactants. Some ways to influence a backward reaction:

• Decreasing reactant concentration: The system will shift to produce more reactants.
• Increasing product concentration: This encourages the reaction to form more reactants.

Understanding the backward reaction is crucial for predicting and manipulating chemical reactions effectively.

Effect of Concentration Changes

The Effect of Concentration Changes in a chemical equilibrium reflects in how the system responds to re-establish equilibrium. According to Le Chatelier's Principle, any alteration in concentration causes the equilibrium position to change. Here are the basic effects of varying concentration:

• Increasing reactant concentration: Promotes the forward reaction, producing more products.
• Decreasing reactant concentration: Shifts the system towards the backward reaction, regenerating reactants.
• Increasing product concentration: Favors the backward reaction, leading to more reactants.
• Removing products: Generally encourages the forward reaction, aiming to replace the lost products.

Through understanding these principles, one can predict the behavior of reactions in various conditions, crucial for practical applications in chemistry.