   Chapter 18, Problem 35PS

Chapter
Section
Textbook Problem

Using values of ΔfG°, calculate ΔrG° for each of the following reactions at 25 °C. Which are product-favored at equilibrium? (a) 2 K(s) + Cl2(g) → 2 KCI(s) (b) 2 CuO(s) → 2 Cu(s) + O2(g) (c) 4 NH3(g) + 7 O2(g) → 4 NO2(g) + 6 H2O(g)

(a)

Interpretation Introduction

Interpretation:

The value of ΔrG for the given reaction 2K(s) + Cl2(g)2KCl(s) at 25 °C should be calculated and should be identified that whether the reaction is product-favoured at equilibrium.

Concept introduction:

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

ΔrG°=nΔfG°(products)nΔfG°(reactants)

Explanation

The standard free energy change for the formation of KCl(s) is calculated below.

The Appendix L referred for the standard free energy change values.

The standard free energy change value of KCl(s) is 408.77 kJ/mol.

The standard free energy change value of K(s) is 0 kJ/mol.

The standard free energy change value of Cl2(g) is 0 kJ/mol.

The balanced chemical equation is,

2K(s) + Cl2(g)2KCl(s)

The expression for the free energy change is:

ΔrG°=nΔfG°(products)nΔfG°(reactants)=[(2 mol KCl(s)/mol-rxn)ΔfG°[KCl(s)][(2 mol K(s)/mol-rxn)ΔfG°[ K(s)]+</

(b)

Interpretation Introduction

Interpretation:

The value of ΔrG for the given reaction 2CuO(s)2Cu(s) + O2(g) at 25 °C should be calculated and should be identified that whether the reaction is product-favoured at equilibrium.

Concept introduction:

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

ΔrG°=nΔfG°(products)nΔfG°(reactants)

(c)

Interpretation Introduction

Interpretation:

The value of ΔrG for the given reaction 4NH3(g) + 7O2(g)4NO2(g) +  6H2O(g) at 25 °C should be calculated and should be identified that whether the reaction is product-favoured at equilibrium.

Concept introduction:

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

ΔrG°=nΔfG°(products)nΔfG°(reactants)

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