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10 November, 09:16

Ethanol, C2H6O, is most often blended with gasoline - usually as a 10 percent mix - to create a fuel called gasohol. Ethanol is a renewable resource and ethanol-blended fuels, like gasohol, appear to burn more efficiently in combustion engines. The heat of combustion of ethanol is 326.7 kcal/mol. The heat of combustion of octane, C8H18, is 1.308*103 kcal/mol. How much energy is released during the complete combustion of 463 grams of octane? kcal Assuming the same efficiency, would 463 grams of ethanol provide more, less, or the same amount of energy as 463 grams of octane? Submit Answer

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  1. 10 November, 09:37
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    This means 463 grams of ethanol would provide less amount of energy

    Explanation:

    Step 1: Data given

    Heat of combustion of ethanol = 326.7 kcal/mol

    The heat of combustion of octane = 1.308*10³ kcal/mol

    Mass of octane = 463 grams

    Molar mass octane = 114.23 g/mol

    Molar mass ethanol = 46.07 g/mol

    Step 2: Calculate moles octane

    Moles octane = mass octane / molar mass octane

    Moles octane = 463 grams / 114.23 g/mol

    Moles octane = 4.05 moles

    Step 3: Calculate energy of combustion of 4.05 moles octane

    Combustion of 1 mol octane gives us: 1.308 * 10³ kcal/mol

    Combustion of 4.05 moles octane gives us 4.05 * 1.308 * 10³ kcal/mol = 5.30 * 10³ kcal

    This means the combustion reaction of 463 grams of octane gives us 5.30 * 10³ kcal

    Step 4:

    Heat of combustion of ethanol = 326.7 kcal/mol

    OR in words: combustion of 1 mol ethanol gives us 326.7 kcal energy

    Moles ethanol = 463 grams / 46.07 g/mol

    Moles ethanol = 10.05 moles

    Since combustion of 1 mol ethanol gives us 326.7 kcal

    10.05 moles ethanol will give us = 10.05 * 326.7 = 3283.3 kcal = 3.28 * 10³ kcal

    5.30 * 10³ kcal > 3.28 * 10³ kcal

    This means 463 grams of ethanol would provide less amount of energy
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