Question

Why does removing a reactant cause an equilibrium shift to the left?

Short answer

Removing a reactant causes an equilibrium shift to the left because the system tries to counteract the stress of the reactant's removal according to Le Chatelier's Principle. This results in the reaction consuming products to form more reactants, reestablishing equilibrium in the system.

Step-by-step solution

Understand the concept of equilibrium

Equilibrium is a state in a reversible chemical reaction where the rate of the forward reaction equals the rate of the reverse reaction, and the concentrations of reactants and products remain constant. In equilibrium, the products and reactants are constantly being formed and consumed, but their concentrations do not change over time.

Learn about Le Chatelier's Principle

Le Chatelier's Principle states that if an external stress is applied to a system at equilibrium, the system will adjust itself to counteract the stress and restore a new equilibrium. In the context of a chemical reaction, a "stress" could be a change in concentration, pressure, or temperature.

Understand the effect of a reactant's removal

When a reactant is removed from the reaction, the balance of the equilibrium is disrupted. According to Le Chatelier's Principle, the system will try to counteract this stress by readjusting its equilibrium to restore balance.

Observe the equilibrium shift to the left

If a reactant is removed, the system will try to increase the concentration of that reactant to compensate for its removal. The reaction will "shift" toward the formation of more reactants by consuming products. This shift is known as a shift to the left, as we usually represent reactions with reactants on the left and products on the right, and the reaction will move towards the reactants’ side to compensate for the imbalance.

Conclusion

Removing a reactant causes an equilibrium shift to the left because, according to Le Chatelier's Principle, the system will respond to the stress of the reactant's removal by increasing its concentration. In shifting left, the reaction will consume products to form more reactants, reestablishing equilibrium in the system.

Key concepts

Le Chatelier's Principle

Le Chatelier’s Principle is a fundamental concept in the study of chemical equilibria. It explains how a system at equilibrium responds when subjected to a change in concentration, pressure, or temperature.
When any of these factors are altered, the equilibrium will shift in a direction that tries to restore balance by counteracting the change.

Le Chatelier's Principle is like a self-correcting mechanism:

• If the concentration of a substance is changed, the equilibrium will shift to reduce the impact.
• Increased pressure will cause the equilibrium to shift towards the side with fewer gas molecules.
• Changes in temperature will cause the equilibrium to shift depending on whether the reaction is exothermic or endothermic.

In essence, the principle allows the system to predictably adjust to disturbances, helping to understand the dynamic nature of chemical equilibria.

Reversible Reactions

Reversible reactions are key to understanding chemical equilibrium as they occur in both forward and reverse directions. This allows the system to dynamically respond to changes.
In these reactions, the products can revert back to the original reactants, establishing a balance over time.
In a reversible reaction:

• The rate of the forward reaction equals the rate of the reverse reaction at equilibrium.
• The concentrations of reactants and products do not change over time, despite continuous reactions occurring.
• They are represented with a double-headed arrow (\(\rightleftharpoons \)) showing that the process is happening in both directions.

These characteristics make reversible reactions unique and critical for maintaining equilibrium in chemical systems. Understanding them helps predict how changes can affect the balance between reactants and products.

Reactant Removal

Removing a reactant is a common stress applied to a system in equilibrium, which is where Le Chatelier's Principle comes into play. When a reactant is removed, the balance is disturbed, prompting the reaction to adjust in a predictable way.

According to Le Chatelier's Principle:

• The system will shift towards the side that produces more of the removed reactant, which we refer to as a "shift to the left."
• This compensatory shift involves converting products back into reactants to make up for the lost reactant concentration.
• This process continues until a new equilibrium is reached, where the rates of the forward and reverse reactions are equal once again.

Understanding the effect of reactant removal helps in predicting the behavior of complex reactions, providing insights into controlling and utilizing chemical processes effectively.