Ethanol is added to gasoline to produce E-15 and E-85. It promotes more complete combustion of the gasoline and is an octane booster. Compare the heats of combustion of 2,2,4-trimethylpentane (1304 kcal/mol) and ethanol (327 kcal/mol). Which has the higher heat of combustion in kcal/mol?

2,2,4-trimethylpentane has the higher heat of combustion in kcal/mol.

Explanation:

Heat of combustion is defined as heat evolved on combustion of 1 mole of a substance.

2,2,4-trimethylpentane has the higher heat of combustion in kcal/mol.

Heat combustion of 2,2,4-trimethylpentane =  (1304 kcal/mol) and

1 mole of 2,2,4-trimethylpentane on combustion gives 8 mole sof carbon dioxide gas and 9 moles of water.

Heat combustion of ethanol = (327 kcal/mol)

1 mole of ethanol on combustion gives 2 moles of carbon dioxide gas and 3 mole of water.

Heat combustion of ethanol < Heat combustion of 2,2,4-trimethylpentane

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