Chapter 18, Problem 33PS

### 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

# Using values of ΔfH° and S°, calculate the standard molar free energy of formation, ΔfG°, for each of the following compounds: (a) CS2(g) (b) NaOH(s) (c) ICl(g) Compare your calculated values of ΔfG° with those listed in Appendix L Which of these formation reactions are predicted to be product-favored at equilibrium at 25 °C?

(a)

Interpretation Introduction

Interpretation:

The the standard molar free energy for formation of CS2(g) should be calculated and compared with the values placed in appendix L. It should be identified that whether the reaction is product favored at equilibrium.

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

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

Explanation

The standard molar free energy of formation for CS2(g) is calculated below.

Given:

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

C(s)+2S(s)CS2(g)ΔfH°(kJ/mol)00+116.7So(J/K×mol)+5.6+32.1+237.8

ΔrH°fH°(products)fH°(reactants)[(1 mol CS2(g)/mol-rxn)ΔfH°[CS2(g)]-[(1 mol C(s)/mol-rxn)ΔfH°[C(s)]+(2 mol S(s)/mol-rxn)ΔfH°[S(s)]] ]

Substituting the respective values,

ΔrH°[(1 mol CS2(g)/mol-rxn)(116.7 kJ/mol)-[(1 mol C(s)/mol-rxn)(0 kJ/mol)+(2 mol S(s)/mol-rxn)(0 kJ/mol)] ]= 116

(b)

Interpretation Introduction

Interpretation:

The the standard molar free energy for formation of NaOH(s) should be calculated and compared with the values placed in appendix L. It should be identified that whether the reaction is product favored at equilibrium.

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

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

(c)

Interpretation Introduction

Interpretation:

The the standard molar free energy for formation of ICl(g) should be calculated and compared with the values placed in appendix L. It should be identified that whether the reaction is product favored at equilibrium.

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

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

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