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UNI CHEM 1020 - Quantitatively Comparing Biofuel to Fossil Fuel

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Chapter 8, Quantitatively Comparing Biofuel to Fossil FuelIf we are going to ‘compare’ two different fuels, we need to look at several different factors. First, How much carbon dioxide does each fuel release into the atmosphere when itis burned? Second, How much ‘theoretical’ energy does each fuel produce? And third, how does the cost compare?To make it fair, we will compare 1 gallon of each fuel.Fuel: Octane, C8H18 Ethanol, C2H5OHDensity: 0.703 g/mL-1 0.789 g/mL-1Compare the emissions with respect to the amount of carbon dioxide produced from thecomplete combustion of one gallon of octane vs. one gallon of ethanol. Step 1: Begin by writing out the balanced equation for the combustion of each fuel:A. OctaneBalanced equation: 2 C8H18 + 25 O2 = 16 CO2 + 18 H2O(12.01 x 8) + (1.008 x 18) = 114.224 g (16 x 2) = 32 g 12.01 + (16 x 2) = 44.01 g (1.008x 2) + 16 Formula mass ____114.2 g__ + ____32 g _____ → ______44 g______ + ______18 g____ Total mass ____228.4 g___ + ___800 g_______ → _______704 g_________ + ______324 g__________ 228+ 800 + 1028 g 704 + 324 = 1028 g B. EthanolBalanced equation: C2H5OH + 3 O2 = 2 CO2 + 3 H2O(12.01 x 2)+(1.008 x 6)+16=46.068 Formula mass ____46.1 g_______ + _____32g____ → ____44 g__________ + ______18 g_____ Total mass ______46 g ______ + _______96 g___ → ______88 g ______ + ________54 g________ 46 + 96 = 142 g 88 + 54 = 142 g Step 2: For each fuel, both octane and ethanol, calculate the mass ratio for determining the amount of carbon dioxide produced compared to how much fuel was burned. Use the total mass (formula mass times the coefficient) for CO2/octane and CO2/ethanol (show your work):A. For Octane: 704 / 228 = 3.088B. For Ethanol: 88/46 = 1.913Which fuel has a higher ratio of CO2 to fuel? ____Octane_______Step 3: using the density of each liquid fuel and volume of a gallon ( in mL) determine the mass (grams) in a gallon of each type of fuel (show all of your work):A. For Octane: .703 x 3,785 ml = 2660.8 g B. For Ethanol: .789 x 3,785 ml = 2986.4 g Step 4: to compare emissions, determine the amount of carbon dioxide that would be emitted into the atmosphere from the combustion of a gallon of that fuel. This can be done using the mass ratio between carbon dioxide and the fuel from the balanced equation and multiplying it by the mass of a gallon:A. For Octane: 3.088 x 2,660.8 = 8,216.5 g B. For Ethanol: 1.913 x 2,986.4 = 5,712.9 g Compare the ‘theoretical’ amount of energy you can get out of one gallon of octane vs. one gallon of ethanol. * recall, back in chapter 3 we compared ethanol to butane. We also looked up the average efficiency of a car engine. (use E100 - this is pure ethanol.) How can I compare the energy content of alternative fuels and gasoline or diesel?Octane ____115,000 BTU/gal__ Ethanol ___ 76,330 Btu/gal______________How much MORE ethanol would you need to burn to get the same amount of energy? Inother words, how many gallons of ethanol would you need to burn to get the same amount of energy as 1 gallon of octane/gasoline? Show your work.115,000/76,330 = 1.507 gallons What does this do to the amount of carbon dioxide that is emitted when ethanol is burned instead of gasoline (octane) if you want to get the same amount of energy out of your car’s engine? Explain. 1.913 x 1.507 = 2.867 This means the emissions will go up for the ethonal because you are having to burn more to get the same amount of energy. How does the cost per gallon compare? You will need to Google current price.Octane _______ $ 2.87________ Ethanol ______$ 1.88______________1.88 x 1.506 =So, if we JUST look at the two different fuels with respect to emissions, which one appears to be the better choice?_______Ethanol_______________And if we JUST look at the two different fuels with respect to the ‘theoretical’ amount of energy in 1 gallon, which one appears to be the better choice?_______Octane_______________Finally, if we also take into consideration the cost/gallon, which one appears to be the better choice?_______Ethanol currently with our gas prices right now_______________OVERALL, which fuel do you think is the better choice?With gas prices up I would have to say Ethanol because of the lower price and lower


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