Chapter 18, Problem 19PS

### 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

# Use S° values to calculate the standard entropy change, ΔrS0, for each of the following processes and comment on the sign of the change. (a) KOH(s) → KOH(aq) (b) Na(g) → Na(s) (c) Br2(ℓ) → Br2(g) (d) HCl(g) → HCl(aq)

(a)

Interpretation Introduction

Interpretation:

The standard entropy change for given KOH(s)KOH(aq) process should be calculated using So values.

Concept Introduction:

Entropy is a measure of the randomness of the system. It is a thermodynamic quantity and an extensive property. It is represented by the symbol S. It can also be defined as the degree of energy dispersal. More the dispersal in energy, more is the value if entropy.

The standard entropy change for any reaction is the sum of standard molar entropies of product, subtracted from the sum of standard molar entropies of reactants. The standard molar entropies are multiplied by the stoichiometric coefficient which is as per the balanced equation.

ΔrS°=nS°(products)nS°(reactants)

Explanation

The standard entropy change for the reaction KOH(s)KOH(aq) is calculated below.

Given: KOH(s)KOH(aq)

Referring Appendix L for values of standard entropies and entered as below,

The standard entropy of KOH(s) is 78.9 J/Kmol.

The standard entropy of KOH(aq) is 91.6 J/Kmol.

The balanced chemical equation is,

KOH(s)KOH(aq)

The expression for the standard entropy change is,

ΔrS°=nS°(products)nS°(reactants)=[[(1 mol KOH(aq)/mol-rxn)S°[KOH(aq)]] [ (1 mol

(b)

Interpretation Introduction

Interpretation:

The standard entropy change for given Na(g)Na(s) process should be calculated using So values.

Concept introduction:

Entropy is a measure of the randomness of the system. It is a thermodynamic quantity and an extensive property. It is represented by the symbol S. It can also be defined as the degree of energy dispersal. More the dispersal in energy, more is the value if entropy.

The standard entropy change for any reaction is the sum of standard molar entropies of product, subtracted from the sum of standard molar entropies of reactants. The standard molar entropies are multiplied by the stoichiometric coefficient which is as per the balanced equation.

ΔrS°=nS°(products)nS°(reactants)

(c)

Interpretation Introduction

Interpretation:

The standard entropy change for given Br2(l)Br2(g) process should be calculated using So values.

Concept introduction:

Entropy is a measure of the randomness of the system. It is a thermodynamic quantity and an extensive property. It is represented by the symbol S. It can also be defined as the degree of energy dispersal. More the dispersal in energy, more is the value if entropy.

The standard entropy change for any reaction is the sum of standard molar entropies of product, subtracted from the sum of standard molar entropies of reactants. The standard molar entropies are multiplied by the stoichiometric coefficient which is as per the balanced equation.

ΔrS°=nS°(products)nS°(reactants)

(d)

Interpretation Introduction

Interpretation:

The standard entropy change for given HCl(g)HCl(aq) process should be calculated using So values.

Concept introduction:

Entropy is a measure of the randomness of the system. It is a thermodynamic quantity and an extensive property. It is represented by the symbol S. It can also be defined as the degree of energy dispersal. More the dispersal in energy, more is the value if entropy.

The standard entropy change for any reaction is the sum of standard molar entropies of product, subtracted from the sum of standard molar entropies of reactants. The standard molar entropies are multiplied by the stoichiometric coefficient which is as per the balanced equation.

ΔrS°=nS°(products)nS°(reactants)

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