   Chapter 18, Problem 39PS

Chapter
Section
Textbook Problem

Determine whether the reactions listed below are entropy-favored or disfavored under standard conditions. Predict how an increase in temperature will affect the value of ΔrG°. (a) N2(g) + 2 O2(g) → 2 NO2(g) (b) 2 C(s) + O2(g) → 2 CO(g) (c) CaO(s) + CO2(g) → CaCO3(s) (d) 2 NaCl(s) → 2 Na(s) + Cl2(g)

(a)

Interpretation Introduction

Interpretation:

It should be determined that whether the given reaction is entropy favorable and should be identified that how increase in temperature will affect the value of ΔrGo.

Concept introduction:

The Gibbs free energy or the free energy change is a thermodynamic quantity represented by ΔrGo. It is 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.

Entropy for any reaction is expressed as,

ΔrS°nS°(products)nS°(reactants)

A reaction is said to be entropy-favored if the value of entropy change for reaction is positive.

Explanation

The value of ΔGo, ΔHo and ΔSo is calculated below.

Given:

The Appendix L referred for the values of standard entropies and enthalpies.

N2(g)+2O2(g)2NO2(g)ΔfH°(kJ/mol)0033.1So(J/K×mol)191.56205.07240.04

ΔrH°=fH°(products)fH°(reactants)=[(2 mol NO2(g)/mol-rxn)ΔfH°[NO2(g)]-[(1 mol N2(g)/mol-rxn)ΔfH°[N2(g)]+(2 mol O2(g)/mol-rxn)ΔfH°[O2(g)]] ]

Substituting the respective values

ΔrH°=[(2 mol NO2(g)/mol-rxn)(33.1 kJ/mol)-[(1 mol N2(g)/mol-rxn)(0 kJ/mol)+(2 mol O2(g)/mol-rxn)(0 kJ/mol)] ]=66

(b)

Interpretation Introduction

Interpretation:

It should be determined that whether the given reaction is entropy favorable and should be identified that how increase in temperature will affect the value of ΔrGo.

Concept introduction:

The Gibbs free energy or the free energy change is a thermodynamic quantity represented by ΔrGo. It is 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.

Entropy for any reaction is expressed as,

ΔrS°nS°(products)-nS°(reactants)

A reaction is said to be entropy-favoured if the value of entropy change for reaction is positive.

(c)

Interpretation Introduction

Interpretation:

It should be determined that whether the given reaction is entropy favorable and should be identified that how increase in temperature will affect the value of ΔrGo.

Concept introduction:

The Gibbs free energy or the free energy change is a thermodynamic quantity represented by ΔrGo. It is 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.

Entropy for any reaction is expressed as,

ΔrS°nS°(products)-nS°(reactants)

A reaction is said to be entropy-favoured if the value of entropy change for reaction is positive.

(d)

Interpretation Introduction

Interpretation:

It should be determined that whether the given reaction is entropy favorable and should be identified that how increase in temperature will affect the value of ΔrGo.

Concept introduction:

The Gibbs free energy or the free energy change is a thermodynamic quantity represented by ΔrGo. It is 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.

Entropy for any reaction is expressed as,

ΔrS°nS°(products)-nS°(reactants)

A reaction is said to be entropy-favoured if the value of entropy change for reaction is positive.

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