The automobile fuel called E85 consists of 85% ethanol and

Chapter 3, Problem 90E

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QUESTION:

The automobile fuel called E85 consists of 85% ethanol and 15% gasoline. E85 can be used in so-called “flex-fuel” vehicles (FFVs), which can use gasoline, ethanol, or a mix as fuels. Assume that gasoline consists of a mixture of octanes (different isomers of \(\mathrm{C}_{8} \mathrm{H}_{18}\)), that the average heat of combustion of \(\mathrm{C}_{8} \mathrm{H}_{18}(l)\) is 5400 kJ/mol, and that gasoline has an average density of 0.70 g/mL. The density of ethanol is 0.79 g/mL. (a) By using the information given as well as data in Appendix C, compare the energy produced by combustion of 1.0 L of gasoline and of 1.0 L of ethanol. (b) Assume that the density and heat of combustion of E85 can be obtained by using 85% of the values for ethanol and 15% of the values for gasoline. How much energy could be released by the combustion of 1.0 L of E85? (c) How many gallons of E85 would be needed to provide the same energy as 10 gal of gasoline? (d) If gasoline costs $3.10 per gallon in the United States, what is the break-even price per gallon of E85 if the same amount of energy is to be delivered?

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QUESTION:

The automobile fuel called E85 consists of 85% ethanol and 15% gasoline. E85 can be used in so-called “flex-fuel” vehicles (FFVs), which can use gasoline, ethanol, or a mix as fuels. Assume that gasoline consists of a mixture of octanes (different isomers of \(\mathrm{C}_{8} \mathrm{H}_{18}\)), that the average heat of combustion of \(\mathrm{C}_{8} \mathrm{H}_{18}(l)\) is 5400 kJ/mol, and that gasoline has an average density of 0.70 g/mL. The density of ethanol is 0.79 g/mL. (a) By using the information given as well as data in Appendix C, compare the energy produced by combustion of 1.0 L of gasoline and of 1.0 L of ethanol. (b) Assume that the density and heat of combustion of E85 can be obtained by using 85% of the values for ethanol and 15% of the values for gasoline. How much energy could be released by the combustion of 1.0 L of E85? (c) How many gallons of E85 would be needed to provide the same energy as 10 gal of gasoline? (d) If gasoline costs $3.10 per gallon in the United States, what is the break-even price per gallon of E85 if the same amount of energy is to be delivered?

ANSWER:

Step 1 of 5

(a) Here we have to compare the energy produced by the combustion of 1.0 L of gasoline and of 1.0 L of ethanol by using the above information.

Given:

The automobile fuel called E85 consists of 85% ethanol and 15% gasoline Volume of gasoline \(\left(\mathrm{C}_{8} \mathrm{H}_{18}\right)=1.0 \mathrm{\ L}\)

Volume of ethanol \(\left(\mathrm{C}_{2} \mathrm{H}_{5} \mathrm{OH}\right)=1.0 \mathrm{\ L}\)

Heat of combustion of gasoline = 5400 kJ/mol

Heat of combustion of ethanol = 1234.8 kJ/mol

Density of gasoline = 0.70 g/mL

Density of ethanol = 0.79 g/mL

Molar mass of ethanol = 46.07 g/mol

Molar mass of gasoline = 110.23 g/mol

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