Ethanol, c2h6o, is most often blended with gasoline - usually as a 10 per cent 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 2-methylheptane, c8h18, is 1.306×103 kcal/mol. how much energy is released during the complete combustion of 394 grams of 2-methylheptane ?

assuming the same efficiency, would 394 grams of ethanol provide more, less, or the same amount of energy as 394 grams of 2-methylheptane?

a. more or
b. less or
c. the same amount

4.51 × 10³ kcal

B. less

Explanation:

Let's consider the combustion of 2-methylheptane.

C₈H₁₈ + 12.5 O₂ ⇒  8 CO₂ + 9 H₂O

When 1 mole of C₈H₁₈ burns, 1.306 × 10³ Kcal are released (heat of combustion). The molar mass of C₈H₁₈ is 114 g/mol. Then, for 394 g of C₈H₁₈:

Assuming the same efficiency, would 394 grams of ethanol provide more, less, or the same amount of energy as 394 grams of 2-methylheptane?

Let's consider the combustion of ethanol.

C₂H₆O + 3 O₂ ⇒  2 CO₂ + 3 H₂O

When 1 mole of C₂H₆O burns, 326.7 Kcal are released (heat of combustion). The molar mass of C₂H₆O is 46.0 g/mol. Then, for 394 g of C₂H₆O:

The combustion of 394 g of ethanol provides less energy than the combustion of 394 g of 2-methylheptane.

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