Identifying the Equilibrium Constant Expression

Oct 13, 2025 by wbrum.org 31 views

Introduction

In chemistry, equilibrium constant expressions are used to describe the balance between reactants and products in a chemical reaction. These expressions are crucial in understanding the direction of a reaction and the concentration of reactants and products at equilibrium. In this article, we will focus on identifying the equilibrium constant expression for a specific chemical equation.

The Chemical Equation

The given chemical equation is:

${ 4 \text{HCl}(aq) + \text{O}_2(g) \leftrightarrow 2 \text{H}_2\text{O}(l) + 2 \text{Cl}_2(g) }$

This equation represents the reaction between hydrogen chloride (HCl) and oxygen (O2) to form water (H2O) and chlorine gas (Cl2).

Identifying the Equilibrium Constant Expression

To identify the equilibrium constant expression, we need to follow the law of mass action, which states that the equilibrium constant (K) is equal to the product of the concentrations of the products raised to their stoichiometric coefficients divided by the product of the concentrations of the reactants raised to their stoichiometric coefficients.

Step 1: Write the Law of Mass Action

The law of mass action for the given equation can be written as:

${ K_{eq} = \frac{[\text{products}]^{\text{stoichiometric coefficients}}}{[\text{reactants}]^{\text{stoichiometric coefficients}}} }$

Step 2: Identify the Stoichiometric Coefficients

The stoichiometric coefficients for the given equation are:

2 for H2O
2 for Cl2
4 for HCl
1 for O2

Step 3: Write the Equilibrium Constant Expression

Using the law of mass action and the stoichiometric coefficients, we can write the equilibrium constant expression as:

${ K_{eq} = \frac{[\text{H}_2\text{O}]^2 [\text{Cl}_2]^2}{[\text{HCl}]^4 [\text{O}_2]} }$

Simplifying the Expression

We can simplify the expression by canceling out the common factors:

${ K_{eq} = \frac{[\text{Cl}_2]^2}{[\text{HCl}]^4 [\text{O}_2]} }$

Conclusion

In conclusion, the equilibrium constant expression for the given chemical equation is:

${ K_{eq} = \frac{[\text{Cl}_2]^2}{[\text{HCl}]^4 [\text{O}_2]} }$

This expression represents the balance between the concentrations of chlorine gas, hydrogen chloride, and oxygen at equilibrium.

Answer

The correct answer is:

${ K_{eq} = \frac{[\text{Cl}_2]^2}{[\text{HCl}]^4 [\text{O}_2]} }$

This answer is option A.

Discussion

The equilibrium constant expression is a crucial concept in chemistry that helps us understand the direction of a reaction and the concentration of reactants and products at equilibrium. In this article, we have identified the equilibrium constant expression for a specific chemical equation and simplified it to its most basic form.

Key Takeaways

The equilibrium constant expression is a mathematical representation of the balance between reactants and products in a chemical reaction.
The law of mass action is used to write the equilibrium constant expression.
The stoichiometric coefficients are used to determine the equilibrium constant expression.
The equilibrium constant expression can be simplified by canceling out common factors.

References

Atkins, P. W., & De Paula, J. (2010). Physical chemistry (9th ed.). Oxford University Press.
Chang, R. (2010). Chemistry: The central science (11th ed.). McGraw-Hill.

Glossary

Equilibrium constant expression: A mathematical representation of the balance between reactants and products in a chemical reaction.
Law of mass action: A mathematical law that describes the equilibrium constant expression.
Stoichiometric coefficients: The numbers of moles of each reactant and product in a chemical reaction.

FAQs

Q: What is the equilibrium constant expression? A: The equilibrium constant expression is a mathematical representation of the balance between reactants and products in a chemical reaction.
Q: How is the equilibrium constant expression written? A: The equilibrium constant expression is written using the law of mass action and the stoichiometric coefficients.
Q: What is the significance of the equilibrium constant expression? A: The equilibrium constant expression helps us understand the direction of a reaction and the concentration of reactants and products at equilibrium.
Q&A: Equilibrium Constant Expressions in Chemistry =====================================================

Frequently Asked Questions

Q: What is the equilibrium constant expression?

A: The equilibrium constant expression is a mathematical representation of the balance between reactants and products in a chemical reaction. It is a way to describe the equilibrium state of a reaction, where the concentrations of reactants and products are constant.

Q: How is the equilibrium constant expression written?

A: The equilibrium constant expression is written using the law of mass action and the stoichiometric coefficients. The law of mass action states that the equilibrium constant (K) is equal to the product of the concentrations of the products raised to their stoichiometric coefficients divided by the product of the concentrations of the reactants raised to their stoichiometric coefficients.

Q: What is the significance of the equilibrium constant expression?

A: The equilibrium constant expression helps us understand the direction of a reaction and the concentration of reactants and products at equilibrium. It also helps us predict the equilibrium constant (K) of a reaction, which is a measure of the reaction's tendency to proceed in the forward or reverse direction.

Q: How do I determine the equilibrium constant expression for a given reaction?

A: To determine the equilibrium constant expression for a given reaction, you need to follow these steps:

Write the balanced chemical equation for the reaction.
Identify the stoichiometric coefficients for each reactant and product.
Write the law of mass action for the reaction.
Simplify the expression by canceling out common factors.

Q: What is the difference between the equilibrium constant expression and the equilibrium constant (K)?

A: The equilibrium constant expression is a mathematical representation of the balance between reactants and products in a chemical reaction, while the equilibrium constant (K) is a numerical value that represents the reaction's tendency to proceed in the forward or reverse direction.

Q: How do I calculate the equilibrium constant (K) from the equilibrium constant expression?

A: To calculate the equilibrium constant (K) from the equilibrium constant expression, you need to substitute the concentrations of the reactants and products into the expression and solve for K.

Q: What are some common mistakes to avoid when writing the equilibrium constant expression?

A: Some common mistakes to avoid when writing the equilibrium constant expression include:

Not including the stoichiometric coefficients in the expression.
Not canceling out common factors in the expression.
Not using the correct concentrations of the reactants and products in the expression.

Q: How do I use the equilibrium constant expression to predict the direction of a reaction?

A: To use the equilibrium constant expression to predict the direction of a reaction, you need to compare the equilibrium constant (K) to the reaction quotient (Q). If K > Q, the reaction will proceed in the forward direction. If K < Q, the reaction will proceed in the reverse direction.

Q: What are some real-world applications of the equilibrium constant expression?

A: Some real-world applications of the equilibrium constant expression include:

Predicting the direction of a reaction in a chemical plant.
Designing a chemical process to optimize the yield of a product.
Understanding the behavior of a reaction in a biological system.

Conclusion

In conclusion, the equilibrium constant expression is a powerful tool in chemistry that helps us understand the balance between reactants and products in a chemical reaction. By following the steps outlined in this article, you can determine the equilibrium constant expression for a given reaction and use it to predict the direction of the reaction.