The automobile fuel called E85 consists of 85 % ethanol and 15 % gasoline. E85 c

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 C8H18), that the average heat of combustion of C8H18(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 note from your instructor:

For Part A, start with the given L of gasoline and use the density of the gasoline as well as the molar mass of  C8H18 to determine the moles of gasoline. Once you have found the moles of gasoline you will use the provided heat of combustion to determine the energy produced. You do not need to use Appendix C because you are using the provided heat of combustion.

For Part B, do the same with the ethanol. You will use the heat of combustion for ethanol from the extra credit homework problem 5.79. If you did not do the that homework problem, you will need to write the balanced equation for the combustion of ethanol paying attention to the phases. Use the phase of gas for the water. Then calculate the heat of the combustion reaction from the heats of formation in Table C.

For Part C, you will need to use a weighted average. This is the same formula we used to determine the average atomic mass.

For Part D, you are starting with the given gallons of gasoline and will need to use the heat of combustion produced for the given liters of gasoline as a conversion factor to determine the energy produced from the given gallons. The heat of combustion produced from the liters of gasoline is from Part A. Now take the energy produced from the gallons of gas and use that as the given. Using the heat of combustion produced for the liters of E85 from Part C, determine the gallons of E85 necessary to produce that much energy.

For Part E, you will use the gallons of gasoline from part D and the gallons of E 85 from part D.

1. How many gallons of E85 would be needed to provide the same energy as 30 gal of gasoline

2.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?

Explanation / Answer

1. C8H18 + 25/2O2 ------> 8CO2 + 9H2O   H = 5400KJ/mol

5400KJ of energy is released when one mole of C8H18 undergoes combustion.

30gal of gsoline = 30 X 3.785 = 113.55L = 113550mL

mass of 113550mL = Density X volume = 0.7 X 113550 = 79485g

79485g of C8H18 = 79485 / 114 = 697.24moles

Energy released 697.24 moles of gasoline = 697.24 X 5400 = 3765078.94KJ

Weighted average Molar mass of E85 = 44X0.5 + 114 X 0.15 = 54.5g

Mass of Gasolin in 54.5g = 54.5 X 0.15 = 8.175g

Energy released by 8.175g of gasoline = (5400 X 8.175) / 114 = 387.23KJ

Mass of ethanol in 54.5g = 54.5 X 0.85 = 46.325g

Energy released by 46.325g of ethanol = (1367 X 46.325) / 44 = 1439.23KJ

H (combustion) for ethanol = 1367KJ/mol

Total energy released by one mole OR 54.5G of E85 = 1439.23 + 387.23 =1826.46KJ

1KJ of energy will be produced by 54.5 / 1826.46 = 0.0298g of E85

MASS REQUIRED TO PRODUCE 3765078.94KJ OF ENERGY (AS produced by 30gal of gasoline)

= 3765078.94 X 0.0298 = 112346.7g

Volume = mass / density

volume of 112346.7g = 112346.7 0 0.79 = 142211.04mL = 142.211L

142.211L = 142.211 / 3.87 = 37.57 Gallons

2. Inormation is incomplete for question 2. Price of ethnol shoul have been give.

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