Question

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 heptane, C₇H₁₆, is 1.151×10³ kcal/mol. How much energy is released during the complete combustion of 348 grams of heptane?

Assuming the same efficiency, would 348 grams of ethanol provide more, less, or the same amount of energy as 348 grams of heptane? More, less, or the same amount? Please type the answers! :)

Answer 1

heat of combution of heptane = 1.151 X 10³ Kcal/mol = 1151 Kcal/mol

that mean 1 mole of heptane after complete combution produce heat = 1151 Kcal/mol

molar mass of heptane = 100.21 gm/mol then 348 gm heptane = 348 / 100.21 = 3.4727 mole

1 mole heptane produce heat = 1151 Kcal then 3.4727 mole heptane produce heat = 3.4727 X 1151 = 3997 Kcal

348 gm heptane produce heat = 3997 Kcal

heat of combution of ethanol = 326.7 Kcal/mol

that mean 1 mole of ethanol after complete combution produce heat = 326.7 Kcal/mol

molar mass of ethanol = 46.07 gm/mol then 348 gm ethanol = 348 / 46.07 = 7.5537 mole

1 mole ethanol produce heat = 326.7 Kcal then 7.5537 mole ethanol produce heat = 7.5537 X 326.7 = 2467.8 Kcal

348 gm ethanol produce heat = 2467.8 Kcal

348 gm ethanol produce less heat than 348 gm heptane