Chemistry & Chemical Reactivity
Chemistry & Chemical Reactivity
9th Edition
ISBN: 9781133949640
Author: John C. Kotz, Paul M. Treichel, John Townsend, David Treichel
Publisher: Cengage Learning
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Chapter 21, Problem 92GQ
Interpretation Introduction

Interpretation:

To determine the ΔrG° for the reaction of silver with HX where X is a halogen.

Concept introduction:

The Gibbs free energy or the free energy change is a thermodynamic quantity represented by ΔrG. It can be calculated in a similar manner as entropy and enthalpy.  The expression for the free energy change is:

ΔrG°=nΔfG°(products)nΔfG°(reactants)

It is related to entropy and entropy by the following expression,

ΔrG=ΔrHTΔrS

Here, ΔrH is the change in enthalpy and ΔrS is the change in entropy.

Expert Solution & Answer
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Answer to Problem 92GQ

The ΔrG for the reaction of silver with hydrogen fluoride is +79.4 kJ/mol-rxn.

The ΔrG for the reaction of silver with hydrogen chloride is 14.67 kJ/mol-rxn.

The ΔrG for the reaction of silver with hydrogen bromide is 43.45 kJ/mol-rxn.

The ΔrG for the reaction of silver with hydrogen iodide is 64.63 kJ/mol-rxn.

Explanation of Solution

The ΔrG for the reaction of silver with hydrogen halide is calculated below.

Given:

Refer to Appendix L for the values of standard free energies.

For X=F,

The given reaction is,

  Ag(s)+HF(g)AgF(s)+12H2(g)

The ΔfG° for AgF(s) is 193.8 kJ/mol.

The ΔfG° for HF(g) is 273.2 kJ/mol.

The ΔfG° for H2(g) is 0 kJ/mol.

The ΔfG° for Ag(s) is 0 kJ/mol.

The expression for free energy change is,

ΔrG°=nΔfG°(products)nΔfG°(reactants)=[[(1 mol AgF(s)/mol-rxn)ΔfG°[AgF(s)]+(0.5 mol H2(g)/mol-rxn)ΔfG°[H2(g)]][(1 mol Ag(s)/mol-rxn)ΔfG°[Ag(s)]+(1 mol HF(g)/mol-rxn)ΔfG°[HF(g)]] ] 

Substitute the values,

ΔrG°=[[(1 mol AgF(s)/mol-rxn)(193.8 kJ/mol)+(0.5 mol H2(g)/mol-rxn)(0 kJ/mol)][(1 mol Ag(s)/mol-rxn)(0 kJ/mol)+(1 mol HF(g)/mol-rxn)(273.2 kJ/mol)] ] =+79.4 kJ/mol-rxn

For X=Cl,

The given reaction is,

  Ag(s)+HCl(g)AgCl(s)+12H2(g)

The ΔfG° for AgCl(s) is 109.76 kJ/mol.

The ΔfG° for HCl(g) is 95.09 kJ/mol.

The ΔfG° for H2(g) is 0 kJ/mol.

The ΔfG° for Ag(s) is 0 kJ/mol.

The expression for free energy change is,

ΔrG°=nΔfG°(products)nΔfG°(reactants)=[[(1 mol AgCl(s)/mol-rxn)ΔfG°[AgCl(s)]+(0.5 mol H2(g)/mol-rxn)ΔfG°[H2(g)]][(1 mol Ag(s)/mol-rxn)ΔfG°[Ag(s)]+(1 mol HCl(g)/mol-rxn)ΔfG°[HCl(g)]] ] 

Substitute the values,

ΔrG°=[[(1 mol AgCl(s)/mol-rxn)(109.76 kJ/mol)+(0.5 mol H2(g)/mol-rxn)(0 kJ/mol)][(1 mol Ag(s)/mol-rxn)(0 kJ/mol)+(1 mol HCl(g)/mol-rxn)(95.09 kJ/mol)] ] =14.67 kJ/mol-rxn

For X=Br,

The given reaction is,

  Ag(s)+HBr(g)AgBr(s)+12H2(g)

The ΔfG° for AgBr(s) is 96.90 kJ/mol.

The ΔfG° for HBr(g) is 53.45 kJ/mol.

The ΔfG° for H2(g) is 0 kJ/mol.

The ΔfG° for Ag(s) is 0 kJ/mol.

The expression for free energy change is,

ΔrG°=nΔfG°(products)nΔfG°(reactants)=[[(1 mol AgBr(s)/mol-rxn)ΔfG°[AgBr(s)]+(0.5 mol H2(g)/mol-rxn)ΔfG°[H2(g)]][(1 mol Ag(s)/mol-rxn)ΔfG°[Ag(s)]+(1 mol HBr(g)/mol-rxn)ΔfG°[HBr(g)]] ] 

Substitute the values,

ΔrG°=[[(1 mol AgBr(s)/mol-rxn)(96.90 kJ/mol)+(0.5 mol H2(g)/mol-rxn)(0 kJ/mol)][(1 mol Ag(s)/mol-rxn)(0 kJ/mol)+(1 mol HBr(g)/mol-rxn)(53.45 kJ/mol)] ] =43.45 kJ/mol-rxn

For X=I,

The given reaction is,

  Ag(s)+HI(g)AgI(s)+12H2(g)

The ΔfG° for AgI(s) is 66.19 kJ/mol.

The ΔfG° for HI(g) is 1.56 kJ/mol.

The ΔfG° for H2(g) is 0 kJ/mol.

The ΔfG° for Ag(s) is 0 kJ/mol.

The expression for free energy change is,

ΔrG°=nΔfG°(products)nΔfG°(reactants)=[[(1 mol AgI(s)/mol-rxn)ΔfG°[AgI(s)]+(0.5 mol H2(g)/mol-rxn)ΔfG°[H2(g)]][(1 mol Ag(s)/mol-rxn)ΔfG°[Ag(s)]+(1 mol HI(g)/mol-rxn)ΔfG°[HI(g)]] ] 

Substitute the values,

ΔrG°=[[(1 mol AgI(s)/mol-rxn)(66.19 kJ/mol)+(0.5 mol H2(g)/mol-rxn)(0 kJ/mol)][(1 mol Ag(s)/mol-rxn)(0 kJ/mol)+(1 mol HI(g)/mol-rxn)(1.56 kJ/mol)] ] =64.63 kJ/mol-rxn

The free energy change for the reaction of silver with hydrogen fluoride is positive and the reaction is not spontaneous. The rest three reactions are spontaneous.

Conclusion

The ΔrG for the reaction of silver with hydrogen fluoride is +79.4 kJ/mol-rxn.

The ΔrG for the reaction of silver with hydrogen chloride is 14.67 kJ/mol-rxn.

The ΔrG for the reaction of silver with hydrogen bromide is 43.45 kJ/mol-rxn.

The ΔrG for the reaction of silver with hydrogen iodide is 64.63 kJ/mol-rxn.

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Chapter 21 Solutions

Chemistry & Chemical Reactivity

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