Chapter 18, Problem 78GQ

### 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

# Calculate the entropy change for dissolving HCl gas in water at 25 °C. Is the sign of ΔrS° what you expected? Why or why not?

Interpretation Introduction

Interpretation:

The entropy change for dissolving HCl(g) in water at 25oC should be calculated and the sign of ΔrS° should be identified.

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 entropy change for dissolving HCl(g) in water at 25 °C is calculated below.

Given:

The Appendix L referred for the values of standard entropies.

The standard entropy of HCl(g) is 186.2 J/Kmol.

The standard entropy of HCl(aq) is 56.5 J/Kmol.

The given reaction is, HCl(g)HCl(aq)

The expression for the standard entropy change is,

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

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