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

Short answer

The backward reaction is favoured by options (a) and (c).

Step-by-step solution

Understanding the Reaction Equilibrium

Chemical equilibrium is reached in a reversible reaction when the rates of the forward and backward reactions are equal. At this point, the concentrations of reactants and products remain constant.

Le Châtelier's Principle

Le Châtelier's Principle states that if a dynamic equilibrium is disturbed by changing the conditions, the position of equilibrium shifts to counteract the change and restore equilibrium.

Analyzing Option (a)

Decreasing the concentration of one of the reactants will shift the equilibrium towards the reactants, attempting to increase their concentration to restore equilibrium. This shift favours the backward reaction.

Analyzing Option (b)

Increasing the concentration of one of the reactants will shift the equilibrium towards the products to decrease the reactant concentration, thus favouring the forward reaction.

Analyzing Option (c)

Increasing the concentration of one or more of the products will shift the equilibrium towards the reactants in an attempt to decrease the excess product, thus favouring the backward reaction.

Analyzing Option (d)

Removal of at least one of the products at regular intervals will shift the equilibrium towards the products to increase their concentration, thus favouring the forward reaction.

Key concepts

Le Châtelier's Principle

In the fascinating world of chemistry, Le Châtelier's Principle serves as a fundamental guideline. This principle helps us understand how equilibrium responds to changes. Imagine a bustling market. If a new stall opens selling a unique product, other stalls might adjust their stock to maintain a balance in the market. Similarly, in a chemical system at equilibrium, any change in conditions will prompt the system to shift in a way that counteracts the change. This change could be in concentration, temperature, or pressure. Every time there is a shift, the system tries to restore equilibrium by favoring either the forward or backward reaction.

• Introduced by Henri Louis Le Châtelier
• Helps predict the direction of the shift when conditions change
• Balances out any disturbances in the equilibrium state

Understanding this principle allows chemists to manipulate reactions, optimizing conditions to yield maximum product or to study reaction behaviors under varying circumstances. This principle is not just limited to theoretical applications but has practical importance in industries for chemical synthesis and manufacturing processes.

Reaction Rates

Reaction rates refer to how fast a chemical reaction proceeds. In a balanced chemical equilibrium, the rate of the forward reaction equals the rate of the backward reaction. Like a well-choreographed dance, the molecules move in step with each other, forming products and reactants at equal speeds. If we imagine our dance slows down or speeds up due to an external change like temperature, it affects how quickly or slowly the dancers move. Reaction rates are influenced by:

• Concentration of reactants
• Temperature
• Presence of a catalyst

When a reaction's rate changes, the equilibrium position can shift to restore balance. For example, increasing the temperature usually increases the reaction rates leading to a potential shift in equilibrium. Understanding these rates and how they interact with Le Châtelier's Principle helps us direct chemical processes efficiently.

Concentration Changes

Concentration changes play a pivotal role in chemical equilibria. Consider concentration like the amount of seasoning in a recipe. Just as adding too much salt can alter the flavor balance, changing the concentration of reactants or products in a reaction can shift the equilibrium. Through Le Châtelier's Principle, we can predict how a system that experiences a change in concentration will shift to reestablish equilibrium. If you:

• Increase reactant concentration - The system will shift towards the products to consume the extra reactants.
• Decrease reactant concentration - The system will shift towards the reactants to try and produce more of what is missing.
• Increase product concentration - Equilibrium will shift towards the reactants to adjust for the excess product.
• Decrease product concentration - Encourages a shift towards forming more products.

These rules help chemists anticipate the outcomes of concentration adjustments, which is essential in controlling industrial reactions or laboratory experiments.

Equilibrium Shifts

In a balancing act of chemical reactions, understanding equilibrium shifts is crucial. Equilibrium shifts are the system's response to changes in conditions. They help maintain a state of balance. Imagine a seesaw that is perfectly level. If a child jumps onto one end, the seesaw tips. To even it out, either weight must be added to the other side, or the same child must change position. Chemical equilibria work similarly. Alterations in concentration, temperature, or pressure can cause the position of equilibrium to shift in a direction that minimizes the effect of the change.

• Shift to the right - Favors the forward reaction, producing more products.
• Shift to the left - Favors the backward reaction, producing more reactants.

The ability to predict and control these shifts allows for optimized industrial synthesis, drug formulation, and efficient chemical process management. Mastery of how and why equilibrium shifts occur ensures successful manipulation of chemical reactions for desired results.