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# Fuel Efficiency : Octane versus Ethanol

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If we use octane (C8 H18 ) as the representative of what is contained in gasoline, and compare it to ethanol (C2H5OH), currently a promising substitute for gasoline, what will be the energy difference on a per gram basis for the two? For the reaction of octane with oxygen to produce carbon dioxide and gaseous water, 48.1 kJ of heat are evolved per gram of octane burned. For ethanol, 26.8 kJ of heat are evolved per gram of ethanol burned.
The density of octane is 0.7025 g/cm and the density of ethanol is 0.7893 g/cm . If burning octane in an automobile is 20% efficient (i.e., 20% of the energy produced is used to move the car) and burning ethanol is 25% efficient, which fuel will have the larger tank, and by how much, to have the same mileage capability?

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If we use octane (C8 H18 ) as the representative of what is contained in gasoline, and compare it to ethanol (C2H5OH), currently a promising substitute for gasoline, what will be the energy difference on a per gram basis for the two. For the reaction of ...

#### Solution Summary

This solution uses efficiencies of burning octane and burning ethanol to compare the size of a fuel tank needed to provide the same amount of energy.

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