Chapter 14: Chemical Equilibrium Quiz

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Questions and Answers

What is the significance of the equilibrium constant K in a chemical reaction?

It indicates the speed of the reaction.

It changes with varying temperature.

It represents the ratio of reactants and products at equilibrium. (correct)

It can only be calculated if the reaction goes to completion.

According to the law of mass action, what can be said about the value of the equilibrium constant at constant temperature?

It varies based on the concentration of products only.

It increases as the reaction favors the reactants.

It remains constant regardless of reactant concentrations. (correct)

It is determined solely by the temperature of the reaction.

In the reaction 2NO2 (g) ⇆ N2O4 (g), what does it mean when the backward reaction is favored?

The reaction proceeds only in the forward direction.

More N2O4 will be present at equilibrium than NO2.

No products will be formed at equilibrium.

More NO2 will be produced than N2O4. (correct)

Which of the following describes the law of mass action?

It describes a constant ratio of concentrations at equilibrium. Signup and view all the answers

What would a high equilibrium constant K value indicate about the reaction's equilibrium position?

The reaction heavily favors the products. Signup and view all the answers

What defines a chemical system reaching equilibrium?

The concentrations of reactants and products remain constant. Signup and view all the answers

Which of the following observations indicates that a reaction has reached chemical equilibrium?

The intensity of one color remains constant. Signup and view all the answers

In the example of nitrogen dioxide (NO2) converting to dinitrogen tetroxide (N2O4), what does the decrease in brown color signify?

The system may have reached equilibrium. Signup and view all the answers

What is a common misconception regarding reactions and equilibrium?

All reactions must be complete for equilibrium to occur. Signup and view all the answers

Which statement accurately describes the nature of a system at equilibrium?

Products are formed at a rate equal to the rate of reactants forming. Signup and view all the answers

What can be inferred if a reaction involves a color change that stabilizes at a light-brown color?

Some reactants and products are still present in the system. Signup and view all the answers

When calculating the concentrations of reactants and products at equilibrium, what must be considered?

The equilibrium constant and reaction conditions. Signup and view all the answers

Which characteristic is NOT associated with a system at chemical equilibrium?

The reaction occurs only in one direction. Signup and view all the answers

What does it indicate if the equilibrium constant K is much greater than 1?

The equilibrium favors the products. Signup and view all the answers

If K is less than 0.1, what can be inferred about the favorability of the reaction?

The equilibrium favors the reactants. Signup and view all the answers

In the context of equilibrium, how many equilibrium positions can exist for a specific system?

An infinite number of equilibrium positions. Signup and view all the answers

What is the equilibrium expression for the reaction N2 (g) + 3H2 (g) → 2NH3(g)?

$K = \frac{[NH3]^2}{[N2][H2]^3}$ Signup and view all the answers

What remains consistent across different equilibrium concentrations within experimental error?

The equilibrium constant. Signup and view all the answers

If K = 6x10^{-2} at 500 °C, what can be inferred about the position of equilibrium?

Favoring primarily reactants. Signup and view all the answers

What can influence the position of equilibrium but not the equilibrium constant?

Temperature change. Signup and view all the answers

If two separate experiments show different equilibrium concentrations, what conclusion can be drawn about K?

K will remain constant within experimental error. Signup and view all the answers

What does the equilibrium constant K depend on?

The temperature and the ratio of concentrations Signup and view all the answers

What happens to the equilibrium expression if the reaction is reversed?

It is the reciprocal of the original expression Signup and view all the answers

How is the equilibrium expression modified if the original reaction is multiplied by a factor n?

It is raised to the power of n Signup and view all the answers

Why are the equilibrium constant K values typically written without units?

They are constant regardless of concentration Signup and view all the answers

Which substances are excluded from the equilibrium expression?

Pure solids and pure liquids Signup and view all the answers

What is the effect of initial concentrations on the equilibrium position?

They can shift the equilibrium position but do not affect K Signup and view all the answers

For the reaction N2 (g) + 3H2 (g) ⇄ 2NH3 (g), what is the expression for K?

$\frac{[NH3]^2}{[N2][H2]^3}$ Signup and view all the answers

What does the equilibrium constant K indicate at a given temperature?

The ratio of products to reactants at equilibrium Signup and view all the answers

Study Notes

Concept of Equilibrium

Reactions can either proceed to completion or stop before reaching completion, resulting in chemical equilibrium.
At equilibrium, the concentrations of reactants and products remain constant over time.

Characteristics of Chemical Equilibrium

Example: The reaction between nitrogen dioxide (NO2) and dinitrogen tetroxide (N2O4) demonstrates that the system reaches equilibrium without becoming colorless.
The intensity of the brown color of NO2 stabilizes at a light brown, indicating a balance between forward and reverse reactions.

Equilibrium Constant (K)

Established by Guldberg and Waage, the law of mass action describes the equilibrium condition through a constant ratio of concentrations at constant temperature.
K remains constant for a given reaction at a specified temperature, reflecting the balance between products and reactants.

Understanding K's Value

If K > 1, products are favored at equilibrium (reaction lies to the right).
If K < 1, reactants are favored (reaction lies to the left).
Values greater than 10 indicate a strong preference for products, while values less than 0.1 indicate a strong preference for reactants.

Writing Equilibrium Expressions

For the reaction N2 (g) + 3H2 (g) ⇄ 2NH3 (g), the equilibrium expression K = [NH3]^2 / ([N2][H2]^3).
The equilibrium constant is dimensionless and excludes solids or liquids in the expression.

Equilibrium Positions

Different sets of concentrations can yield the same K value at equilibrium, indicating multiple equilibrium positions exist for a specific reaction.
The equilibrium constant is unaffected by initial concentrations but depends on the ratio of concentrations.

Key Takeaways

The equilibrium expression is the reciprocal when the reaction is reversed and is raised to the power of n if multiplied by factor n.
K values are consistent for the same reaction at a constant temperature, regardless of initial reactant or product concentrations.

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Description

Test your understanding of the concepts surrounding chemical equilibrium and the equilibrium constant. This quiz covers how chemical systems reach equilibrium, the characteristics of this state, and how to calculate concentrations of reactants and products at equilibrium.