Ch.19 - Chemical Thermodynamics

Brown - Chemistry: The Central Science 15th Edition

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Brown 15th Edition

Ch.19 - Chemical Thermodynamics

Problem 9a

Chapter 19, Problem 9a

Consider a reaction A₂(𝑔) + B₂(𝑔) ⇌ 2 AB(𝑔), atoms of A shown in red in the diagram and atoms of B shown in blue. (a) If 𝐾_𝑐 = 1, which box represents the system at equilibrium?

Verified step by step guidance

Identify the equilibrium constant (Kc) for the reaction. In this case, Kc is given as 1, which means the concentrations of reactants and products are equal at equilibrium.

Write the expression for the equilibrium constant Kc for the reaction: Kc = [AB]^2 / ([A2][B2]).

Examine each box in the diagram to count the number of molecules of A2, B2, and AB. Remember that A2 and B2 are diatomic molecules and AB is a product formed from one atom of A and one atom of B.

Calculate the Kc for each box using the formula from step 2. Since Kc = 1, find the box where the calculated Kc equals 1.

The box where Kc equals 1 represents the system at equilibrium. This is because the ratio of the concentration of the products squared to the concentration of the reactants equals the equilibrium constant.

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Key Concepts

Here are the essential concepts you must grasp in order to answer the question correctly.

Chemical Equilibrium

Chemical equilibrium occurs in a reversible reaction when the rates of the forward and reverse reactions are equal, resulting in constant concentrations of reactants and products. In this state, the system appears static, but molecular activity continues. The equilibrium constant (Kc) quantifies the ratio of product concentrations to reactant concentrations at equilibrium, providing insight into the position of equilibrium.

Equilibrium Constant (Kc)

The equilibrium constant (Kc) is a numerical value that expresses the ratio of the concentrations of products to reactants at equilibrium, raised to the power of their stoichiometric coefficients. A Kc value of 1 indicates that the concentrations of reactants and products are equal at equilibrium, suggesting that neither side is favored. This concept is crucial for predicting the direction of a reaction and understanding the balance between reactants and products.

Le Chatelier's Principle

Le Chatelier's Principle states that if a dynamic equilibrium is disturbed by changing the conditions (such as concentration, temperature, or pressure), the system will adjust to counteract the change and restore a new equilibrium. This principle helps predict how a system will respond to changes, such as adding or removing reactants or products, and is essential for understanding the behavior of chemical reactions at equilibrium.

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Related Practice

Textbook Question

The accompanying diagram shows how entropy varies with temperature for a substance that is a gas at the highest temperature shown. (c) If this substance is a perfect crystal at T = 0 K, what is the value of S at this temperature?

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Textbook Question

Which of the following processes are spontaneous and which are nonspontaneous: (d) lightning

Which of the following processes are spontaneous and which are nonspontaneous: (e) formation of CH₄ and O₂ molecules from CO₂ and H₂O at room temperature and 1 atm of pressure?

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Textbook Question

Predict the signs of ΔH and ΔS for this reaction. Explain your choice.

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Textbook Question

Which of the following processes are spontaneous?

a. the melting of ice cubes at −10 °C and 1 atm pressure

b. separating a mixture of N₂ and O₂ into two separate samples, one that is pure N₂ and one that is pure O₂

c. alignment of iron filings in a magnetic field

d. the reaction of hydrogen gas with oxygen gas to form water vapor at room temperature

e. the dissolution of HCl(g) in water to form concentrated hydrochloric acid

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Consider a reaction A2(𝑔) + B2(𝑔) ⇌ 2 AB(𝑔), atoms of A shown in red in the diagram and atoms of B shown in blue. (a) If 𝐾𝑐 = 1, which box represents the system at equilibrium?

Verified video answer for a similar problem:

Key Concepts

Chemical Equilibrium

Equilibrium Constant (Kc)

Le Chatelier's Principle

Consider a reaction A₂(𝑔) + B₂(𝑔) ⇌ 2 AB(𝑔), atoms of A shown in red in the diagram and atoms of B shown in blue. (a) If 𝐾_𝑐 = 1, which box represents the system at equilibrium?