Chemistry & Chemical Reactivity
Chemistry & Chemical Reactivity
10th Edition
ISBN: 9781337399074
Author: John C. Kotz, Paul M. Treichel, John Townsend, David Treichel
Publisher: Cengage Learning
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Chapter 20, Problem 47GQ

(a)

Interpretation Introduction

Interpretation: The enthalpy of combustion of ethanol and isooctane, the fuel which release more CO2 and better fuel in terms of energy production should be given.

Concept introduction:

Enthalpy of combustion: At standard conditions when one mole of substance is burnt completely in presence of oxygen, the enthalpy change involved is called enthalpy of combustion.

ΔH0comb=nΔH0fproducts-nΔH0freactants

(a)

Expert Solution
Check Mark

Answer to Problem 47GQ

Isooctane release more energy than ethanol.

Explanation of Solution

Given the combustion of ethanol and isooctane:

EthanolC2H5OH(l)+3O2(g)2CO2(g)+3H2O(l)

ΔH0fof CO2=-393.509kJ/molΔH0fof H2O=-285.83kJ/molΔH0fofC2H5OH=-277kJ/molΔH0fofO2=0kJ/mol

Enthalpy of combustion can be calculated by the equation:

ΔH0comb=nΔH0fproducts-nΔH0freactants

ΔH0comb=[2×-393.509+3×-285.83]-[-277]=-1367.5kJ/mol

IsooctaneC8H18(l)+252O2(g)8CO2(g)+9H2O(l)

ΔH0fof CO2=-393.509kJ/molΔH0fof H2O=-285.83kJ/molΔH0fofC8H18=-259.3kJ/molΔH0fofO2=0kJ/mol

Enthalpy of combustion can be calculated by the equation:

ΔH0comb=nΔH0fproducts-nΔH0freactants

ΔH0comb=[8×-393.509+9×-285.83]-[-259.3]=-5461.2kJ/mol

Isooctane releases more energy per kilogram.

(b)

Interpretation Introduction

Interpretation: compare the enthalpy of combustion of ethanol and isooctane and the fuel which release more CO2 per kilogram should be determined.

Concept introduction:

Enthalpy of combustion: At standard conditions when one mole of substance is burnt completely in presence of oxygen, the enthalpy change involved is called enthalpy of combustion.

ΔH0comb=nΔH0fproducts-nΔH0freactants

(b)

Expert Solution
Check Mark

Answer to Problem 47GQ

Ethanol produces less CO2 per kilogram.

Explanation of Solution

ΔH0comb of C2H5OH is found to be -1367.5kJ/mol and ΔH0comb of C8H18 is found to be -5461.2kJ/mol.

EthanolC2H5OH(l)+3O2(g)2CO2(g)+3H2O(l)

One mole of ethanol produces two moles of CO2.

The number of moles CO2 released by ethanol will be 43.4molCO2

IsooctaneC8H18(l)+252O2(g)8CO2(g)+9H2O(l)

One mole of isooctane produces eight moles of CO2.

The number of moles CO2 released by the number of moles CO2 released by isooctane will be 70molCO2

Isooctane release more amount of CO2.

(c)

Interpretation Introduction

Interpretation: The better fuel in terms of energy production and greenhouse gases should be determined.

Concept introduction:

Enthalpy of combustion: At standard conditions when one mole of substance is burnt completely in presence of oxygen, the enthalpy change involved is called enthalpy of combustion.

ΔH0comb=nΔH0fproducts-nΔH0freactants

(c)

Expert Solution
Check Mark

Answer to Problem 47GQ

Isooctane releases more energy, but it releases more CO2 too.

Explanation of Solution

In-order to say whether ethanol or isooctane is a better fuel, we have to compare its energy release.

Comparing ethanol and isooctane, isooctane releases more energy.

But the problem is that when we compare the CO2 release by both ethanol and isooctane, isooctane releases more CO2.CO2 is green-house gas and if the amount is increased, it will pollute the atmosphere. Isooctane releases more amount of CO2 than ethanol.

On the basis of energy release isooctane can be considered as a better fuel, but when the release of CO2 is considered it will not be a better fuel.

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Chapter 20 Solutions

Chemistry & Chemical Reactivity

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