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 octane, C8H18, is 1.308×103 kcal/mol. How much energy is released during the complete combustion of 406 grams of octane ? kcal Assuming the same efficiency, would 406 grams of ethanol provide more, less, or the same amount of energy as 406 grams of octane?

Answer 1

Explanation:

Given,

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

It means that combustion of 1 mole of octane produces 1.308×10³ kcal of energy

Given mass = 406 g

Molar mass of octane = 114.23 g/mol

The formula for the calculation of moles is shown below:

$moles = \frac{Mass\ taken}{Molar\ mass}$

Thus,

$Moles= \frac{406\ g}{114.23\ g/mol}$

Moles of octane = 3.5542 moles

Combustion of 3.5542 moles produces 3.5542×1.308×10³ kcal of energy

Energy released from 406 grams of octane = 4.649×10³ kcal

Also given,

The heat of combustion of ethanol = 326.7 kcal/mol

It means that combustion of 1 mole of octane produces 326.7 kcal of energy

Given mass = 406 g

Molar mass of octane = 46.07 g/mol

The formula for the calculation of moles is shown below:

$moles = \frac{Mass\ taken}{Molar\ mass}$

Thus,

$Moles= \frac{406\ g}{46.07\ g/mol}$

Moles of octane = 8.8127 moles

Combustion of 8.8127 moles produces 8.8127×326.7 kcal of energy

Energy released from 406 grams of ethanol= 2879.11 kcal = 2.879×10³ kcal

It is less.