   Chapter 13, Problem 56E

Chapter
Section
Textbook Problem

# At a particular temperature, Kp = 0.25 for the reaction N 2 O 4 ( g ) ⇌ 2 NO 2 ( g ) a. A flask containing only N2O4 at an initial pressure of 4.5 atm is allowed to reach equilibrium. Calculate the equilibrium partial pressures of the gases.b. A flask containing only NO2 at an initial pressure of 9.0 atm is allowed to reach equilibrium. Calculate the equilibrium partial pressures of the gases.c. From your answers to parts a and b, does it matter from which direction an equilibrium position is reached?

(a)

Interpretation Introduction

Interpretation: The equilibrium constant (Kp) value for the decomposition reaction of N2O4 is given. The equilibrium partial pressures at the given initial pressure values are to be calculated.

Concept introduction: The state when the reactants involved in a chemical reaction and the products formed in the reaction exist in concentrations having no further tendency to change is known as an equilibrium state of the reaction. When the equilibrium constant is expressed in terms of pressure, it is represented as Kp.

To determine: The equilibrium partial pressures of the species involved.

Explanation

Given

The initial partial pressure of N2O4(g) (PN2O4) is 4.5atm.

The equilibrium constant (Kp) is 0.25.

The reaction that takes place between hydrogen gas and nitrogen gas is,

N2O4(g)2NO2(g)

At equilibrium, the equilibrium ratio is expressed by the formula,

Kp=PartialpressureofproductsPartialpressureofreactants

Where,

• Kp is the equilibrium constant in terms of partial pressure.

The equilibrium ratio for the given reaction is,

Kp=(PNO2)2(PN2O4) (1)

The equilibrium partial pressure values are represented as,

N2O4(g)2NO2(g)Initial(atm)4.50Change(atm)-x+2xEquilibrium(atm)4.5-x2x

According to the ICE table formed,

The equilibrium partial pressure of N2O4(g) (PN2O4) is 4.5x.

The equilibrium partial pressure of NO2(g) (PNO2) is 2x.

Substitute the values of PN2O4 and PNO2 in equation (1)

(b)

Interpretation Introduction

Interpretation: The equilibrium constant (Kp) value for the decomposition reaction of N2O4 is given. The equilibrium partial pressures at the given initial pressure values are to be calculated.

Concept introduction: The state when the reactants involved in a chemical reaction and the products formed in the reaction exist in concentrations having no further tendency to change is known as an equilibrium state of the reaction. When the equilibrium constant is expressed in terms of pressure, it is represented as Kp.

To determine: The equilibrium partial pressures of the species involved.

(c)

Interpretation Introduction

Interpretation: The equilibrium constant (Kp) value for the decomposition reaction of N2O4 is given. The equilibrium partial pressures at the given initial pressure values are to be calculated.

Concept introduction: The state when the reactants involved in a chemical reaction and the products formed in the reaction exist in concentrations having no further tendency to change is known as an equilibrium state of the reaction. When the equilibrium constant is expressed in terms of pressure, it is represented as Kp.

To determine: If it matters that from which direction an equilibrium position is reached.

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