Chapter 18, Problem 90SCQ

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074

Chapter
Section

### Chemistry & Chemical Reactivity

10th Edition
John C. Kotz + 3 others
ISBN: 9781337399074
Textbook Problem

# Consider the formation of NO(g) from its elements.N2(g) + O2(g) ⇄ 2 NO(g) (a) Calculate Kp at 25 °C. Is the reaction product-favored at equilibrium at this temperature? (b) Assuming ΔrH° and ΔrS° are nearly constant with temperature, calculate ΔrG° at 700 °C. Estimate Kp from the new value of ΔrG° at 700 °C. Is the reaction product-favored at equilibrium at 700 °C? (c) Using Kp at 700 °C, calculate the equilibrium partial pressures of the three gases if you mix 1.00 bar each of N2 and O2.

(a)

Interpretation Introduction

Interpretation:

The equilibrium constant for formation of NO(g) from its elements should be calculated and identified that whether the reaction is product favoured at equilibrium at given temperature.

Concept introduction:

The Gibbs free energy or the free energy change is a thermodynamic quantity represented by ΔrGo. It can be calculated in a similar manner as entropy and enthalpy.  The expression for the free energy change is:

ΔrG°fG°(products)fG°(reactants)

ΔGo is related to the equilibrium constant K by the equation,

ΔrGo= -RTlnKp

The rearranged expression is,

Kp= eΔrGoRT

It is also related to entropy and entropy by the following expression,

ΔGo=ΔHo- TΔSo

Here, ΔHo is the change in enthalpy and ΔSo is the change in entropy.

Explanation

The value of Kp at 25 °C  is calculated below.

Given:

The Appendix L referred for values of standard free energy values.

The given reaction is,

N2(g) + O2(g)2NO(g)

The ΔrGo for NO(g) is 86.58 kJ/mol.

The ΔrGo for O2(g) is 0 kJ/mol.

The ΔrGo for N2(g) is 0 kJ/mol.

ΔrG°fG°(products)fG°(reactants)=[(2 mol NO(g)/mol-rxn)ΔfG°[NO(g)]-[(1 mol N2(g)/mol-rxn)ΔfG°[N2(g)]+(1 mol O2(g)/mol-rxn)ΔfG

(b)

Interpretation Introduction

Interpretation:

The ΔrGo value for formation of NO(g) from its elements should be calculated at 700oC and Kp for respective ΔrGo at 700oC should be estimated also it should be identified that the reaction is product favoured at equilibrium at this given temperature.

Concept introduction:

The Gibbs free energy or the free energy change is a thermodynamic quantity represented by ΔrGo. It can be calculated in a similar manner as entropy and enthalpy.  The expression for the free energy change is:

ΔrG°fG°(products)fG°(reactants)

ΔGo is related to the equilibrium constant K by the equation,

ΔrGo= -RTlnKp

The rearranged expression is,

Kp= eΔrGoRT

It is also related to entropy and entropy by the following expression,

ΔGo=ΔHo- TΔSo

Here, ΔHo is the change in enthalpy and ΔSo is the change in entropy.

(c)

Interpretation Introduction

Interpretation:

The equilibrium partial pressures of the given three gases should be calculated if they were mixed 1bar of each N2andO2.

Concept introduction:

The Gibbs free energy or the free energy change is a thermodynamic quantity represented by ΔrGo. It can be calculated in a similar manner as entropy and enthalpy.  The expression for the free energy change is:

ΔrG°fG°(products)fG°(reactants)

ΔGo is related to the equilibrium constant K by the equation,

ΔrGo= -RTlnKp

The rearranged expression is,

Kp= eΔrGoRT

It is also related to entropy and entropy by the following expression,

ΔGo=ΔHo- TΔSo

Here, ΔHo is the change in enthalpy and ΔSo is the change in entropy.

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