Problem 5 - Campbell Biology

Question

Which of the following statements correctly describes any chemical reaction that has reached equilibrium? (A) The concentrations of products and reactants are equal. (B) The reaction is now irreversible. (C) Both forward and reverse reactions have halted. (D) The rates of the forward and reverse reactions are equal.

Step-by-Step Solution

Answer

The correct answer is (D).

Step 1 - Understanding Equilibrium

Before analyzing the given statements, understand that chemical equilibrium is the state in which the concentrations of reactants and products remain constant over time. This happens because the rates of the forward and reverse reactions are equal.

Step 2 - Analyze Statement (A)

Statement (A) claims that the concentrations of products and reactants are equal. This is not necessarily true. At equilibrium, the concentrations remain constant but are not required to be equal.

Step 3 - Analyze Statement (B)

Statement (B) claims that the reaction is now irreversible. This is incorrect. At equilibrium, both the forward and reverse reactions are occurring; they just do so at equal rates.

Step 4 - Analyze Statement (C)

Statement (C) claims that both forward and reverse reactions have halted. This is incorrect. At equilibrium, both reactions continue to occur at equal rates.

Step 5 - Analyze Statement (D)

Statement (D) claims that the rates of the forward and reverse reactions are equal. This is the correct description of a chemical reaction at equilibrium.

Step 6 - Conclusion

Based on the definitions and analysis, Statement (D) correctly describes a chemical reaction that has reached equilibrium.

Key Concepts

reaction rates

In a chemical reaction, reaction rates refer to how quickly reactants are transformed into products. This is an important concept when discussing chemical equilibrium.

Rates of reaction can be influenced by many factors, including

• Temperature: Higher temperatures typically increase reaction rates.
• Concentration of Reactants: Higher concentration often leads to an increased rate of reaction.
• Catalysts: These substances speed up the reaction without being consumed.

Understanding the rates of forward and reverse reactions is crucial when analyzing whether a system has reached equilibrium.

equilibrium state

A chemical reaction reaches an equilibrium state when the rates of the forward and reverse reactions are equal. At equilibrium:

• The concentrations of reactants and products remain constant over time.
• The system is dynamic, meaning both forward and reverse reactions still occur.

It's important to note that equilibrium does not mean the reactants and products are in equal amounts, just that their concentrations no longer change. This balance is described by the equilibrium constant, which provides a ratio of product concentrations to reactant concentrations, each raised to the power of their coefficients in the balanced chemical equation.

constant concentrations

When a reaction is at equilibrium, the concentrations of reactants and products remain constant. This does not mean they are equal, but their levels do not change over time.

• Equilibrium can be reached regardless of the initial concentrations of reactants and products.
• Changes in temperature or pressure can shift the equilibrium, altering the concentration of reactants and products.

A change in these conditions can result in a new equilibrium state, where the concentrations might be different, yet still constant and balanced in terms of reaction rates.

forward and reverse reactions

In a chemical reaction, there are two main types of reactions: the forward reaction, where reactants turn into products, and the reverse reaction, where products revert to reactants.

• In the forward reaction, reactants are consumed and products are formed.
• In the reverse reaction, products are consumed and reactants are formed.

When a system reaches equilibrium, both these reactions continue to happen but at equal rates. This balance is what maintains the constant concentrations of reactants and products. So, even though the reaction is still ongoing, it appears stable because the changes are occurring at an equal pace in both directions.