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    Is ethanol or gasoline more cost efficient?

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    As all of you are aware, there is a big push to use ethanol (C2H6O) as a source of fuel for our automobiles, instead of gasoline. Assuming that gasoline can be adequately represented by octane (C8H10), determine how reasonable it is. That is, will individuals actually save any money using ethanol (at approximately $0.83/L) as compared to gasoline (at approximately $1.10/L)? The heats of formation are for: ethanol (-277.63 kJ/mol); octane (-208.45 kJ/mol); water vapor (-241.8 kJ/mol); CO2(g) (-393.5 kJ/mol). Density of ethanol is 0.7893 g/mL and for octane is 0.7025 g/mL. Assume that the efficiency of burning both is the same.

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    Solution Preview

    So first we need balanced equations and then find the dH values for each reaction.

    C2H5OH + 3O2 = 2CO2 + 3H2O

    dH = [(2x-393.5) + (3x-241.8)] - (1x-277.63) = -1234.77 kJ for 1 mol of C2H5OH burned.

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    Solution Summary

    The expert determines if ethanol or gasoline is more cost efficient.