Question

Which of the following will cause the value of the equilibrium constant for a specific reaction to change? (a) change in the concentration of a reactant or product (b) change in volume of the container (c) change in temperature (d) addition of a catalyst

Short answer

The only factor that causes the equilibrium constant to change is a change in temperature (option c).

Step-by-step solution

Understanding the Effect of Concentration

Option (a) refers to a change in the concentration of a reactant or product. This doesn't change the equilibrium constant of a reaction itself. According to Le Chatelier's principle, if the concentration of a reactant or product is changed, the system will shift in the direction that will counteract this change until a new equilibrium state is reached.

Explaining Impact of Volume Change

Option (b) refers to a change in the volume of the container. However, the equilibrium constant is not affected by the volume of the container. A change in volume will alter the pressure, and the system will adjust to counter this change (according to Le Chatelier's principle), but the equilibrium constant stays the same.

Interpreting the Role of Temperature

Option (c) refers to a change in temperature. This is the only factor that can change the value of the equilibrium constant for a chemical reaction. When the temperature changes, the reaction reaches a new equilibrium state and the equilibrium constant (K) will change, reflecting the favorability of the reaction at the new temperature.

Addition of a Catalyst

Option (d) indicates the addition of a catalyst to the reaction. A catalyst speeds up both the forward and reverse reactions equally, so it doesn’t change the equilibrium constant. It simply helps the system reach equilibrium more quickly.

Key concepts

Le Chatelier's Principle

Le Chatelier's principle is a fundamental concept in chemistry that explains how systems at equilibrium respond to disturbances. When a system at equilibrium experiences a change in concentration, pressure, or temperature, the equilibrium will shift to counteract the effect of the disturbance. This principle helps predict the direction in which a reaction will proceed when subjected to these changes.

• When a concentration of a reactant or product is altered, the system shifts to restore balance. Add more reactant, and the reaction will go forward to produce more product. Increase the product, and the reaction will shift backward to produce more reactant.
• If the pressure increases due to a decrease in volume, the system adjusts by shifting toward the side with fewer gas molecules. If the pressure decreases, the system shifts toward the side with more gas molecules.
• Temperature changes, notably, affect the equilibrium constant (which we’ll discuss in the next section).

By applying Le Chatelier's principle, we can better understand the behavior of reactions under various conditions and predict their outcomes. It's a powerful tool for chemists in both laboratory and industrial settings.

Temperature Effect on Equilibrium

Temperature is unique among reaction conditions because it can change the equilibrium constant, denoted as \( K \). Each chemical reaction has its own specific \( K \) value, which is constant at a given temperature. However, if the temperature changes, \( K \) will change accordingly.
For an exothermic reaction (one that releases heat), increasing the temperature will shift the equilibrium to the left, favoring the reactants. Conversely, lowering the temperature will shift it to the right, favoring the products. The opposite is true for endothermic reactions, where increasing temperature favors the products and decreasing temperature favors the reactants.
Changes in temperature will alter the \( K \) value as it reflects the new balance of reactant and product concentrations at the altered temperature. Understanding this allows chemists to predict how temperature adjustments can influence the yield of desired products in a reaction.

Role of Catalysts in Reactions

Catalysts play a vital role in reactions; however, they do not change the equilibrium constant. Instead, catalysts work by providing an alternative reaction pathway with a lower activation energy, allowing the reaction to achieve equilibrium faster.
It’s important to understand that catalysts speed up both the forward and reverse reactions equally. This means that while the presence of a catalyst can make a reaction occur more quickly, it doesn’t affect the concentrations of reactants and products at equilibrium.
This property of catalysts is highly useful in industry and research, where increased reaction speed is beneficial, but without altering the equilibrium position or the \( K \) value. Catalysts are essential in processes where time and efficiency are crucial, ensuring higher productivity while maintaining the chemical properties of the reaction.