   Chapter 18, Problem 55E

Chapter
Section
Textbook Problem

# Glucose is the major fuel for most living cells. The oxidative breakdown of glucose by our body to produce energy is called respiration. The reaction for the complete combustion of glucose is C 6 H 12 O 6 ( s )   +  6O 2 ( g ) → 6 CO 2 ( g ) + 6 H 2 O ( l ) If this combustion reaction could be harnessed as a fuel cell, calculate the theoretical voltage that could be produced at standard conditions. (Hint: Use Δ G f ∘ values from Appendix 4.)

Interpretation Introduction

Interpretation: The theoretical voltage that could be produced at standard conditions of the given reaction for the complete combustion of glucose is to be calculated.

Concept introduction: Gibbs free energy is a thermodynamic quantity that is used to calculate the maximum work of reversible reaction performed by a system. It is equal to the difference between the enthalpy and the product of entropy at absolute temperature. Voltage is defined as the measure of energy per unit charge available from the redox reaction to carry out the reaction.

To determine: The theoretical voltage that could be produced at standard conditions for the given reaction.

Explanation

Explanation

Given

The given reactions are,

Oxidation: C6H12O6+6H2O6CO2+24H++24e (1)

Reduction: 6O2+24H++24e12H2O (2)

The overall reaction is,

C6H12O6+6O26CO2+6H2O (3)

The standard Gibbs free energy (ΔGο) is the change in free energy when one mole of a compound is formed from its constituent elements in their standard states. It is represented as follows,

ΔGrxnο=ΔGProductοΔGreactantο

Where,

ΔGProductο is the sum of free energies of products.

ΔGreactantο is the sum of free energies of reactants.

The table representing the values of standard free energy of formation (ΔGfο) of reactants and products is as follows,

SubstanceΔGfο(kJ/mol)Glucose910.5CO2394.4O20H2O237.14

The ΔGrxnο is calculated by using the expression

ΔGrxnο=ΔGProductοΔGreactantο

Substitute the value of ΔGreactantο and ΔGproductο in the above expression

ΔGrxnο=ΔGProductοΔGreactantοΔGrxnο=([(6)ΔG

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