   Chapter 18, Problem 92SCQ

Chapter
Section
Textbook Problem

The normal melting point of benzene, C6H6, is 5.5 °C. For the process of melting, what is the sign of each of the following?(a) ΔrH°(b) ΔrS°(c) ΔrG° at 5.5 °C(d) ΔrSG° at 0.0 °C(e) ΔrG° at 25.0 °C

(a)

Interpretation Introduction

Interpretation:

The sign of enthalpy change for benzene should be identified.

Concept introduction:

The Gibbs free energy or the free energy change is a thermodynamic quantity represented by ΔGo. It is related to entropy and entropy by the following expression,

ΔGo= ΔHo- TΔSo

The sign of ΔGo should be positive for a product-favored reaction. Thus, spontaneous reactions are referred to those that have negative free energy formation.

The sign of ΔSo should be positive for an entropy-favored reaction and the sign of ΔHo should be negative for an enthalpy favored-reaction.

Explanation

The melting of benzene is an endothermic process with a ΔHo value of 9.87 kJ/mol

(b)

Interpretation Introduction

Interpretation:

The sign of entropy change for benzene should be identified.

Concept introduction:

The Gibbs free energy or the free energy change is a thermodynamic quantity represented by ΔGo. It is related to entropy and entropy by the following expression,

ΔGo= ΔHo- TΔSo

The sign of ΔGo should be positive for a product-favored reaction. Thus, spontaneous reactions are referred to those that have negative free energy formation.

The sign of ΔSo should be positive for an entropy-favoured reaction and the sign of ΔHo should be negative for an enthalpy favoured-reaction.

(c)

Interpretation Introduction

Interpretation:

The sign of ΔGo for benzene at 5.5oC should be identified.

Concept introduction:

The Gibbs free energy or the free energy change is a thermodynamic quantity represented by ΔGo. It is related to entropy and entropy by the following expression,

ΔGo= ΔHo- TΔSo

The sign of ΔGo should be positive for a product-favored reaction. Thus, spontaneous reactions are referred to those that have negative free energy formation.

The sign of ΔSo should be positive for an entropy-favoured reaction and the sign of ΔHo should be negative for an enthalpy favoured-reaction.

(d)

Interpretation Introduction

Interpretation:

The sign of ΔGo for benzene at 0.0oC should be identified.

Concept introduction:

The Gibbs free energy or the free energy change is a thermodynamic quantity represented by ΔGo. It is related to entropy and entropy by the following expression,

ΔGo= ΔHo- TΔSo

The sign of ΔGo should be positive for a product-favored reaction. Thus, spontaneous reactions are referred to those that have negative free energy formation.

The sign of ΔSo should be positive for an entropy-favoured reaction and the sign of ΔHo should be negative for an enthalpy favoured-reaction.

(e)

Interpretation Introduction

Interpretation:

The sign of ΔGo for benzene at 25.0oC should be identified.

Concept introduction:

The Gibbs free energy or the free energy change is a thermodynamic quantity represented by ΔGo. It is related to entropy and entropy by the following expression,

ΔGo= ΔHo- TΔSo

The sign of ΔGo should be positive for a product-favored reaction. Thus, spontaneous reactions are referred to those that have negative free energy formation.

The sign of ΔSo should be positive for an entropy-favoured reaction and the sign of ΔHo should be negative for an enthalpy favoured-reaction.

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