Question

Which of the following statements is(are) true? Correct the false statement(s). a. When a reactant is added to a system at equilibrium at a given temperature, the reaction will shift right to reestablish equilibrium. b. When a product is added to a system at equilibrium at a given temperature, the value of K for the reaction will increase when equilibrium is reestablished. c. When temperature is increased for a reaction at equilibrium, the value of K for the reaction will increase. d. When the volume of a reaction container is increased for a system at equilibrium at a given temperature, the reaction will shift left to reestablish equilibrium. e. Addition of a catalyst (a substance that increases the speed of the reaction) has no effect on the equilibrium position.

Short answer

a. True b. False. Corrected statement: When a product is added to a system at equilibrium at a given temperature, the value of K for the reaction stays constant when equilibrium is reestablished. c. Depends on the reaction: True for endothermic reactions; False for exothermic reactions. d. False. Corrected statement: When the volume of a reaction container is increased for a system at equilibrium at a given temperature, the reaction will shift in the direction with more gas moles to reestablish equilibrium. e. True

Step-by-step solution

Statement a

When a reactant is added to a system at equilibrium at a given temperature, the reaction will shift right to reestablish equilibrium. According to Le Chatelier's principle, if a change is made to a system at equilibrium, the system will shift in the direction that reduces the change. Therefore, when we add more reactants, the reaction will indeed shift right to use up the added reactants and reestablish equilibrium. This statement is true.

Statement b

When a product is added to a system at equilibrium at a given temperature, the value of K for the reaction will increase when equilibrium is reestablished. The equilibrium constant (K) is only affected by temperature changes. It stays constant for a particular reaction at a given temperature. Adding a product will cause the reaction to shift left, consuming the added product to reestablish equilibrium. However, the value of K will not change. Therefore, this statement is false. Corrected statement: When a product is added to a system at equilibrium at a given temperature, the value of K for the reaction stays constant when equilibrium is reestablished.

Statement c

When temperature is increased for a reaction at equilibrium, the value of K for the reaction will increase. This statement is true for endothermic reactions and false for exothermic reactions. For endothermic reactions, increasing the temperature increases the value of K because the reaction can "absorb" additional heat by shifting to the right. Conversely, for exothermic reactions, the additional heat will cause the reaction to shift to the left, decreasing the value of K. Corrected statement: When temperature is increased for an endothermic reaction at equilibrium, the value of K for the reaction will increase.

Statement d

When the volume of a reaction container is increased for a system at equilibrium at a given temperature, the reaction will shift left to reestablish equilibrium. According to Le Chatelier's principle, if we increase the volume, the reaction will move in the direction that has a larger number of moles of gas to reestablish equilibrium. The direction depends on the specific reaction. This statement is not necessarily true. Incorrect statement: When the volume of a reaction container is increased for a system at equilibrium at a given temperature, the reaction will shift in the direction with more gas moles to reestablish equilibrium.

Statement e

Addition of a catalyst (a substance that increases the speed of the reaction) has no effect on the equilibrium position. A catalyst speeds up both the forward and reverse reactions equally, which means that equilibrium is reached faster, but it has no effect on the position of equilibrium. Thus, this statement is true.

Key concepts

Le Chatelier's Principle

Le Chatelier's Principle is a fundamental concept in chemical equilibrium. It describes how a system at equilibrium responds to changes. When there is a change (in concentration, temperature, or pressure), the system shifts to offset the change and reestablish equilibrium. For example, if additional reactants are introduced to the system, the equilibrium shifts towards the products, making the reaction proceed to the right. This is to consume the excess reactants. Alternatively, if a product is added, the equilibrium shifts towards the reactants, moving the reaction to the left.

Key points of Le Chatelier's Principle include:

• Adding reactants shifts the equilibrium to the right, favoring product formation.
• Adding products shifts the equilibrium to the left, encouraging more reactant formation.
• Removing reactants or products causes the equilibrium to shift to replace them.
• The principle helps predict the direction of the shift but does not quantify the extent of the shift.

Equilibrium Constant (K)

The Equilibrium Constant, denoted as \( K \), is a numerical value that characterizes the position of equilibrium for a reversible chemical reaction. This constant depends solely on temperature and provides insight into the relative concentrations of products and reactants at equilibrium.

For a generic reaction \( aA + bB \rightleftharpoons cC + dD \), the expression for \( K \) is: \[K = \frac{ [C]^c [D]^d }{ [A]^a [B]^b }\]Here, the concentrations \( [A], [B], [C], \) and \( [D] \) are those of the reactants and products at equilibrium. Important aspects to remember about \( K \):

• It is specific to a particular reaction at a given temperature.
• It doesn't change with changes in concentration, pressure, or catalysts.
• A large \( K \) indicates that products are favored, while a small \( K \) indicates that reactants are favored.

Effect of Temperature on Equilibrium

Temperature changes can significantly impact chemical equilibrium and the value of the equilibrium constant \( K \). The direction of this effect depends on whether the reaction is endothermic or exothermic.

In **endothermic reactions**, where heat is absorbed, an increase in temperature pushes the equilibrium towards the products, resulting in a higher \( K \). Conversely, in **exothermic reactions**, where heat is released, an increase in temperature shifts the equilibrium towards the reactants, lowering \( K \). Here are the implications simplified:

• Endothermic reactions: ↑ Temperature → ↑ \( K \) → Equilibrium shifts right (to products).
• Exothermic reactions: ↑ Temperature → ↓ \( K \) → Equilibrium shifts left (to reactants).

This behavior aligns with Le Chatelier's Principle because heat can be considered a "reactant" in endothermic reactions and a "product" in exothermic ones.

Consequently, balancing temperature is crucial for optimizing yields in industrial and laboratory settings.

Catalysts in Reaction Dynamics

Catalysts play a pivotal role in the dynamics of chemical reactions by lowering the activation energy required, thereby increasing the reaction rate.

Despite their impact on reaction speed, catalysts do not change the position of equilibrium. Instead, they help the system achieve equilibrium more swiftly by speeding up both the forward and reverse reactions equally. This means that while the equilibrium is attained faster, the relative concentrations of reactants and products remain unchanged at equilibrium.

Understanding these points about catalysts is essential:

• Catalysts lower activation energy, enhancing the reaction rate.
• They do not affect the final equilibrium position or the value of \( K \).
• Catalysts are often used to make reactions economically viable by decreasing the time to reach equilibrium.

In many industrial applications, finding an appropriate catalyst can be the key to efficient production processes.